InfoMagic Standards 1993 July/Disc.iso/ccitt/1988/troff/5_1_07.tro

Text File | 1991-12-13 | 123.9 KB | 4,472 lines

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\fBSUPPLEMENTS\ TO\ SERIES\ P\ RECOMMENDATIONS\fR
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\fBMONTAGE:\ \fR PAGE PAIRE = PAGE BLANCHE
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\fBSupplement\ No.\ 1\fR
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\fBPRECAUTIONS\ TO\ BE\ TAKEN\ FOR\ CORRECT\ \fR \fBINSTALLATION\fR
.EF '%    Volume\ V\ \(em\ Suppl.\ No.\ 1''
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\fBAND\ MAINTENANCE\ OF\ AN\ IRS\fR
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(For this Supplement see Volume V of the \fIOrange Book\fR )
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\fBSupplement\ No.\ 2\fR
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\fBMETHODS\ USED\ FOR\ ASSESSING\ TELEPHONY\ TRANSMISSION\ PERFORMANCE\fR
.EF '%    Volume\ V\ \(em\ Suppl.\ No.\ 2''
.OF '''Volume\ V\ \(em\ Suppl.\ No.\ 2    %'
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\fI(Geneva, 1980; modified at\fR \fIMalaga\(hyTorremolinos, 1984; Melbourne,
1988)\fR
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\fI(Quoted in Recommendation P.80)\fR
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(Contribution from British Telecom)
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.LP
\fB1\fR     \fBIntroduction\fR
.sp 1P
.RT
.PP
This Supplement gives brief descriptions of the methods for assessing telephony
transmission performance that are recommended by the CCITT or have
been employed over Study Periods 1968\ to\ 1980 in studying Questions assigned
to Study Group\ XII. Some of the methods are already fully described in
Recommendations and these will merely be listed here with
reference to the appropriate Recommendation. Other methods are also described
in detail elsewhere; the essential features of these are given here with
a
brief description of how they are conducted, with reference to descriptions
published elsewhere.
.RT
.sp 2P
.LP
\fB2\fR     \fBList of methods\fR \v'3p'
.sp 1P
.RT
.LP
    a)
    loudness comparison for speech
(reference equivalents and loudness ratings);
.LP
    b)
    articulation (AEN) ratings;
.LP
    c)
    listening opinion tests;
.LP
    d)
    conversation opinion tests;
.LP
    e)
    quantal\(hyresponse detectability tests.
.sp 2P
.LP
\fB3\fR     \fBBrief descriptions and references to more complete\fR
\fBdescriptions\fR
.sp 1P
.RT
.PP
3.1
Loudness comparisons for speech are intended to quantify the
relative level at which speech, transmitted over a given telephone connexion,
reaches the ears of customers while they are listening to a person talking
at the other end. In order to standardize the measuring procedure, the
talking and listening conditions are each controlled in a specified manner.
Circuit noise and room noise are excluded from the determination and so
the results are
governed by the overall mouth\(hyto\(hyear transmission loss of the speech
path being considered. The present recommended method is given in Recommendation\
P.72
(\fIRed\ Book\fR ) and proposals for new methods are to be found in
Question\ 15/XII\ [1]. More general information can be found in
Reference\ [2].
.sp 9p
.RT
.PP
3.2
Articulation measurements
are based on measurement
of the fraction of speech sounds recognized correctly when transmitted and
reproduced over the speech path in question. Circuit noise and room noise at
specified levels should be present and the result is affected by their
levels. Just as for \(sc\ 3.1 above, talking and listening conditions are
controlled. The method recommended by the CCITT is described in former
Recommendation\ P.45
(\fIOrange\ Book\fR ). Other information will be found in Reference\ [2].
.PP
3.3
Listening opinion tests
are conducted using speech
material in the form of sentences and the listeners judge the speech received
over the path according to a given criterion. The method has been widely
used, and further details can be found in Reference\ [2].
.sp 1P
.LP
3.3.1
    \fIMethod of conducting\fR
\fIlistening opinion tests\fR
.sp 9p
.RT
.PP
The speech is usually recorded so that it can be reproduced at a
given level. The recordings for this purpose must be carefully made and
copied so that uncontrolled degradations do not appear. Circuit noise and
room noise may be present, and their effects are taken into account.
.bp
.PP
Two subjective criteria commonly used are loudness preference and
listening effort, for which the following scales are used.
.RT
.LP
    \(em
    Loudness preference scale
:
.LP
    \fIOpinion scale No. 4A\fR
.LP
    A
    Much louder than preferred.
.LP
    B
    Louder than preferred.
.LP
    C
    Preferred.
.LP
    D
    Quieter than preferred.
.LP
    E
    Much quieter than preferred.
.LP
    \(em
    Listening effort scale
:
.LP
    \fIOpinion scale No. 7: Opinions based on the effort required\fR
\fIto understand the meanings of sentences\fR
.LP
    A
    Complete relaxation possible; no effort required.
.LP
    B
    Attention necessary; no appreciable effort required.
.LP
    C
    Moderate effort required.
.LP
    D
    Considerable effort required.
.LP
    E
    No meaning understood with any feasible effort.
.PP
The heading \*Q. |  |  \fIEffort required to understand the meanings of\fR
\fIsentences\fR \*U is particularly important. Without it, the other descriptions
are liable to be seriously misunderstood.
.PP
\fR Experimental design is usually based on a graeco\(hylatin or
hyper\(hygraeco\(hylatin square, in which rows represent listeners, columns
represent the order in which conditions are administered, symbols of the
first alphabet represent circuit conditions, and symbols of other alphabets
represent talkers and lists of sentences. Each cell of the design thus
represents a \*Qrun\*U, in
which a particular list of sentences, recorded by a particular talker, is
replayed via a particular circuit condition to a particular listener at a
particular position in the sequence of conditions presented to that listener.
Within each run the listening level is varied over a number of predetermined
values in random order, one value per group of five sentences, and the
subject votes on one of the above opinion scales at the end of each group.
Rarely some other parameter, such as bandwidth, is varied within each run
instead of
listening level.
.PP
\fR In listening\(hyeffort tests, listeners are specially prone to what
is known as the \*Qenhancement\*U effect: that is, their standards of judgement
are liable to be strongly influenced by the range of quality and listening
level
occurring in the same test, and especially within the same run. It is therefore
important that the circuit conditions chosen should not include too many
bad ones (that is, conditions that will yield a poor listening\(hyeffort score
even with the best listening levels), that every run should cover a range of
listening levels from well above optimum to at least 30\ dB below optimum,
and that within each run at least one group of sentences should be heard
via an
\*Qanchor\*U condition (a good condition with a good listening level).
It is also important that groups and lists of sentences should not vary
too widely in
their intrinsic comprehensibility, and that no subject should hear the same
sentence more than once in the same experiment, because the listening effort
needed to understand a familiar sentence would obviously be reduced.
.PP
\fR The votes using the above scales are scored respectively 4, 3, 2, 1
and\ 0: the mean of these values for each circuit condition is called \*Q
mean  opinion score
\*U. The opinion scores are processed by analysis of variance in order
to verify that the effects due to circuit condition, listening levels,
talkers, listeners and other factors are as expected, to determine their
significance, and to evaluate confidence intervals. It is usual to express
the relationship between listening level and loudness\(hypreference mean
opinion score (scale\ 4A) by fitting an equation describing a straight
line or logistic curve, whereas the relationship between listening level
and listening\(hyeffort mean
opinion score (scale\ 7) is expressed by a fitted quadratic or more complicated
equation; other features of the circuit conditions may also enter as parameters
into these equations.
.PP
Listening tests
using sentence material can also be conducted as pair\(hycomparisons, but
these should be undertaken with due consideration to ensure that subjects
become suitably adapted to each test
condition.
.bp
.RT
.PP
3.4 \fR Conversation tests may be conducted either as interviews
after real customers have made actual calls or as laboratory tests. Further
information regarding methods recommended by the CCITT for the former is
given in Recommendation\ P.82. Laboratory conversation tests are intended
as far as
possible to reproduce under laboratory conditions the actual service conditions
experienced by telephone customers: to this end it is necessary to choose
the circuit conditions and subjects suitably, and to administer the tests
in an
appropriate manner. A method intermediate between field observations and
laboratory tests is that used by the AT&T and called SIBYL (see also
Reference\ [3]). Particulars of the method used by British Telecom
are given below.
.sp 1P
.LP
3.4.1
    \fIMethod for conducting\fR
\fIconversation tests\fR
.sp 9p
.RT
.PP
The need for careful and exhaustive preparations cannot be too
strongly emphasized. It will be obvious to all that the connexions must be
correctly specified and set up, and measured accurately before and after
each experiment; that auxiliary facilities such as dialling and ringing
must be
provided, so that any of the desired connections can be chosen and established
quickly and without error; and that faithful records of the output of each
test must be kept. But some other equally important considerations are
less
obvious. The following gives an outline of a system that takes all these
matters into account, and has been found satisfactory in British
Telecom.
.RT
.sp 1P
.LP
3.4.1.1
    \fIExperimental design\fR
.sp 9p
.RT
.PP
The most suitable designs are of the \fIn\fR \ \(mu\ \fIn\fR  | raeco\(hylatin
square type, where each of \fIn\fR \ pairs of subjects carries out one
conversation on each of \fIn\fR \ circuit conditions. Precision is very
low if\ \fIn\fR is less
than\ 8; at the other extreme it is not practical to expect subjects to
attend on more than four occasions, or to carry out more than four conversations
per visit. Moreover, the total number of conversations, \fIn\fR \ \(mu\
\fIn\fR , increases much more rapidly than\ \fIn\fR . For this reason,\
\fIn\fR is normally limited to the range\ 8 to\ 15 inclusive: graeco\(hylatin
squares (with symbols from two alphabets) exist for all these numbers.
In such a design, the convention is that rows denote
pairs of subjects; columns denote the order of administering the experiment;
symbols of the first alphabet denote circuit conditions (distinguished
not only according to properties of the connections by themselves, but
also according to room noise levels and any other \*Qtreatment\*U factors);
symbols of the second
alphabet denote sets of pictures used as the topic of conversation. No further
.PP
orthogonal factors can be incorporated at all where \fIn\fR \ =\ 10, 14
or\ 15, nor by any simple method when \fIn\fR \ =\ 12; but where \fIn\fR
\ =\ 8, 9, 11 or\ 13, it is possible to construct hyper\(hygraeco\(hylatin
squares with symbols from (\fIn\fR \ \(em\ 3) additional alphabets, which
may be used to govern further orthogonal factors (such as
selection of carbon microphones, choice of calling party, or choice of
crosstalk recording), for each conversation. When the square is not
hyper\(hygraeco\(hylatin these factors must be allocated by some simple
balanced
rotation scheme, but this may give rise to biases that cannot be eliminated
from the results. For this reason the recommended value of\ \fIn\fR is
now\ 13 rather than\ 12 as previously.
.PP
To the basic square is added an extra column at the beginning, having the
same circuit condition and the same picture set for all pairs of subjects.
This column represents a preliminary conversation for each pair of subjects,
which serves to accustom them to the procedure, and to some extent stabilizes
their standards of judgement. Thus each of the\ \fIn\fR pairs of subjects
carries
out (\fIn\fR \ +\ 1) conversations altogether. The results from the preliminary
conversations are not included in the main part of the analysis of results,
but are analyzed separately. Using the same preliminary circuit condition
in
different experiments establishes some common ground between experiments,
but if precise comparisons between results from different experiments are
desired, care must be taken to include replications of several standard
circuit
conditions in each such experiment.
.RT
.sp 1P
.LP
3.4.1.2
    \fIChoice of circuit conditions\fR
.sp 9p
.RT
.PP
Circuit conditions between which particularly precise comparisons are desired
must be included within the same experiment.
.PP
\fR Besides this it is necessary that all subjects in every experiment
should experience more or less the whole range of performance levels: that
is, there should be at least one very good circuit condition, one of near
average performance, and one very poor one, while the rest should not all
cluster too closely about the same mean opinion score value. If one cannot
.bp
.PP
be
confident of
this beforehand, it is advisable to carry out first a short informal test on
the proposed set of circuit conditions, in order to find out whether the
range is in fact covered; if not, the selection of conditions should be
modified
accordingly, otherwise the subjects' opinion scale will be distorted (the
\*Qenhancement\*U effect). Extra circuit conditions, not in themselves
of direct
interest to the experimenter, may be added to bring up the number to\ 9, 11
or\ 13, and to balance the range of performance more effectively.
.PP
\fR Subjects generally expect to experience circuit conditions with
various values of overall loss or sensitivity, which of course has a very
strong influence on performance, and can be varied to provide the required
range of circuit conditions. There are also important interactions between
overall sensitivity and many other degradations. It is therefore highly
desirable, even if overall sensitivity and its interactions are not the main
objects of the investigation, to include some conditions differing from each
other only in overall sensitivity.
.PP
If the investigation cannot be confined to 15 conditions, it is then spread
over several experiments, each concentrating on a well defined
part of the inquiry but overlapping the others so as to provide common
ground.
.RT
.sp 1P
.LP
3.4.1.3
    \fIEligibility of subjects\fR
.sp 9p
.RT
.PP
Subjects taking part in the conversation tests are chosen at random from
the Research Centre personnel, with the provisons that:
.RT
.LP
    a)
    they have not been directly involved in work connected
with assessment of the performance of telephone circuits;
and
.LP
    b)
    they have not participated in any subjective test
whatever for at least the previous six months, and not in a
conversation test for at least one year.
.PP
No steps are taken to balance the numbers of male and female
subjects unless the design of the experiment requires it. Subjects are
arbitrarily paired in the experimental design prior to the test and remain
thus paired for its duration.
.sp 1P
.LP
3.4.1.4
    \fIEnvironment\fR
.sp 9p
.RT
.PP
Subjects are seated in separate
sound\(hyproof cabinets
near the point from which the experiment is controlled. Room noise is fed
in with
the required spectrum (usually the
Hoth spectrum
) at the required level (usually 50\ dBA), measured with a Bruel and Kjaer
Precision Sound Level Meter type\ 2206, used with the \*Q
\fIA\fR weighting
\*U and the \*Qfast\*U meter
characteristic. If different conversations in the same experiment require
different room noise levels, then care is taken to prevent the transitions
from being too obvious to the subjects: ideally, room noise should be changed
only when subjects are out of the sound\(hyproof rooms.
.RT
.sp 1P
.LP
3.4.1.5
    \fIMethods of establishing the connection\fR
.sp 9p
.RT
.PP
The telephone sets used by the subjects are normal in appearance
and feel \(em usually identical to the standard British Telecom
Telephone No.\ 706, unless the experiment specifically concerns handsets of
other types. The means of establishing telephone contact between subjects is
made as realistic as possible. The calling subject, on lifting the handset,
obtains dialling tone, and has to dial or key a prescribed number to obtain
the connection. Ringing tone occurs after a suitable fixed delay, and the
other
party's bell or tone\(hycaller is operated after a further fixed delay. Wrong
numbers are rewarded by the \*QNumber Unobtainable\*U tone.
.RT
.sp 1P
.LP
3.4.1.6
    \fIConversation task\fR
.sp 9p
.RT
.PP
Every effort is made to ensure that conversations are purposeful, and that
subjects have full opportunity to exploit the transmission
capabilities of the test circuit. A task involving sorting pictures into an
order of merit has been found suitable for this purpose and sufficiently
interesting to the subjects. The pictures, covering a wide variety of topics,
are samples of the standard postcard\(hysized illustrations offered for
sale at
several different museums, art galleries and similar institutions. These
cards are individually numbered on the back, and assembled arbitrarily
into sets of six cards each, every set having an exact duplicate.
.bp
.PP
The subject is instructed to consider these pictures for display in
a public place, and, before each conversation, to arrange the cards of a
particular set in his personal order of preference for this purpose; the
other subject does the same with his copy of the same set. When contact
is
established via the test circuit, the subjects have to negotiate an agreed
.PP
order of preference and write this down at the end of the conversation. The
duration of each conversation is thus determined by the subjects themselves.
Occasionally a conversation may be very long because both subjects are
intensely interested in the pictures, or\ \(em as happens in less than\ 1% of
cases\ \(em very short because both have independently chosen the same order of
preference and have little to discuss, but even in these cases it is highly
desirable to allow the subjects to decide for themselves how long to converse.
After the end of the conversation they express independent opinions of
the
connection by marking a form provided: one version of this form is reproduced
in Annex\ A.
.PP
Some variations of the task (such as numbering the same pictures
differently for the two subjects) have been explored, but none has been
definitively adopted. No other type of task has been found to have any
greater advantages for the purpose, though several types have been tried.
.RT
.sp 1P
.LP
3.4.1.7
    \fIPreparations for an\fR n\ \(mu\ n \fIexperiment\fR
.sp 9p
.RT
.PP
From a list of all subjects available, the experimenter randomly
chooses a sufficient number of those eligible according to the criteria
given in \(sc\ 3.4.1.3 above. He contacts these by telephone to ask whether
they are
willing to participate at certain times, which have to be arranged in
such a way that subjects who converse together on their first visit remain
paired for their subsequent visits in the same experiment. A standard letter
is sent to each subject, confirming the time and place of each appointment,
and
explaining in some detail what will be required of the subjects in the
experiment: the text of a typical letter is reproduced in Annex\ B.
.PP
The experimenter prepares schedules, based on the experimental
design, showing in what order conditions must be administered to each pair
of subjects, with which picture sets, which party initiates the call in
each case, and any other necessary details. Space is left for filling in
information that
.PP
becomes available as the experiment proceeds: consecutive conversation
number, duration of conversation, identity of tape reel used for recording,
comments
about faults or unusual events, and so on. Opinion forms (Annex\ A) are also
prepared for each conversation. However, in order to avoid duplicating or
altering too many entries, some items are not filled in until they are
certain: for example, the actual names of the subjects are liable to change
until they actually arrive for their first visit.
.PP
Both in the letter and in any discussions with the subjects, great
care is taken not to communicate to the subjects any knowledge about the
nature of the circuit conditions. The opinion forms do not even carry any
number or
code identifying the circuit condition\ \(em this information is obtained
from the schedule and added to the forms after they have been collected
from the
subjects.
.RT
.sp 1P
.LP
3.4.1.8
    \fIProcedure\fR
.sp 9p
.RT
.PP
When subjects arrive for their first visit, they are asked whether they
have read and understood the letter. Any obscurities are clarified, and
opportunity is given for asking questions. The sound\(hyproof rooms and their
facilities are demonstrated. Subjects are informed how many calls will be
comprised in this visit. Forms are handed to the subjects, and they are then
left to prepare for the preliminary conversation. On subsequent visits the
subjects are merely informed that the procedure will be the same as before,
with possibly a different number of calls.
.PP
At the beginning of each conversation, the subjects take out the
specified picture set from a box on the desk, arrange the pictures in order
of preference, and fill in the appropriate part of the opinion form. When
both
subjects have done this, the experimenter gives one of them the signal to
initiate the call. The subjects are then completely free to determine the
course of the conversation, except that they must not discuss their opinions
of the connection. When they have written down their agreed order of preference
for the pictures, terminated the conversation, and recorded their scores
.PP
(Excellent, Good, Fair, Poor or Bad) and their answer to the \*QDifficulty\*U
question (Yes or No), the experimenter contacts each in turn by telephone to
ask what answer he has given to the \*QDifficulty\*U question; if the answer is
\*QYes\*U, the experimenter asks the subject to explain briefly (in his
own words) the nature of the difficulty. The reply is noted, but neither
the subject nor the experimenter is expected to attempt precise formulations:
it is essential not to prompt the subjects, and in any case the classification
of difficulty
has been found far less useful than the undifferentiated percentage
\*QDifficulty\*U itself.
.bp
.PP
After this the experimenter requests the subject to put away the form in
an envelope provided, and then tells him to start sorting out the next
set of pictures, or, as the case may be, to wait to be released from the
sound\(hyproof room.
.PP
Both the conversations between subjects and the conversations between experimenter
and subject are tape\(hyrecorded.
.RT
.sp 1P
.LP
3.4.1.9
    \fITreatment of results\fR
.sp 9p
.RT
.PP
The results from each conversation comprise two opinions on the
scale Excellent\(hyGood\(hyFair\(hyPoor\(hyBad (scored respectively\ 4,
3, 2, 1,\ 0), two
votes on the Difficulty scale (scored\ 1\ =\ Yes, 0\ =\ No), two speech levels
(measured from tape recordings) and one value of duration. In particular
cases information may be collected about other variables also; for example,
video
recordings may be made in order to observe how subjects hold their
handsets.
.PP
Analysis of variance is applied separately to each variate (opinion
score, speech level,\ etc.) in order to test the significance of
circuit\(hycondition features and other effects, and to find confidence
intervals for the means. With a binary variate like \*QDifficulty\*U this
process must be
regarded with some reservations. There is usually less scope for curve\(hyfitting
than in listening experiments, simply because there are far fewer pairs
of
coordinate values available.
.RT
.sp 1P
.LP
3.5
    \fIQuantal\(hyresponse detectability tests\fR
.sp 9p
.RT
.PP
The best method for obtaining information on the detectability of some
analogous property of a sound (such as echo), as a function of some
objective quantity (such as listening level), is a quantal\(hyresponse method
similar in principle to that mentioned in \(sc\ 3.1 above for loudness
balancing. The main difference is that the subject's response is not a
decision in the
form \*QReference\*U or \*QTest\*U (the designation of the louder of two
circuits), but a vote on a scale such as:
.RT
.LP
    \fIOpinion scale 6A\fR
.LP
    A
    Objectionable
.LP
    B
    Detectable
.LP
    C
    Not detectable
.LP
where B is understood to mean \*QDetectable but not objectionable\*U.
.PP
\fR
Scales of this sort, usually with three points, may be used in a variety
of quantal\(hyresponse tests; for example the scale as shown above may
be used where the stimulus is echo, reverberation, sidetone, voice\(hyswitching
mutilation, or interfering tones, while crosstalk and perhaps echo in some
circumstances may be judged on the scale Intelligible\ \(em Detectable\
\(em Not
detectable.
.PP
It is sometimes permissible to regard these votes as opinion scores, with
values 2, 1, 0 respectively, and treat them in the same sort of way as
one would treat listening or conversation opinion scores. But this is often
unsatisfactory because the decisions on such a scale as\ 6A are not really
equivalents of responses on a continuous scale\ \(em as votes on such scales
as\ 4A may be legitimately taken to be\ \(em but effectively embody two
distinct
dichotomies (for example detectable/not detectable and objectionable/not
objectionable), which though not independent may nevertheless call different
.PP
psychological processes into action: in other words, Objectionability or
Intelligibility differs in kind, not merely in degree, from Detectability,
and often has a different standard deviation. For this reason a more profitable
method of analysis is to express the probability of response according
to each dichotomy separately, as a function of some objective variable,
by fitting
probit or logit equations, and then using the quantiles or other parameters
as a basis of comparison between circuit conditions, in a manner analogous
to that used in applying articulations scores.
.PP
The actual conduct of experiments of this type resembles that of
listening\(hyeffort tests (see \(sc\ 3.3.1\ above), but there are some
differences. In particular it is advisable that the first presentation
of the signal in each
run should be at a high listening level, so that the listener is left in no
doubt what kind of signal is a candidate for his decisions. Where sidetone
or echo is involved, the subject will be required to talk as well as listen.
.PP
\fR Simple audiometric measurements, as described in Recommendation\ P.78,
are usually performed on subjects who participate in these experiments,
so that results can be expressed relative to their threshold of hearing.
.bp
.PP
\fR For examples of the application of these techniques, see
References\ [4] and\ [5].
.PP
Noise and other disturbances are sometimes investigated by means
of responses on a scale with many more points; for example, Opinion scale\ 5
with seven points ranging from \*QInaudible\*U to \*QIntolerable\*U. These
scales are more nearly of the quantized\(hycontinuum type, like Opinion
scale\ 4A, and can be treated similarly.
.RT
.sp 2P
.LP
\fB4\fR \fBRecommendations and other CCITT studies relying on Methods a)
to e) of \(sc\ 2 above:\fR \v'3p'
.sp 1P
.RT
.LP
    a)
    Many Recommendations include requirements based originally
on reference equivalents, later on corrected reference
equivalents, and more recently on loudness ratings of which
Recommendations\ P.12 (\fIOrange\ Book\fR ), G.101\ [6], G.103\ [7],
G.111\ [8], G.120\ [9] and G.121\ [10] are examples.
.LP
    b)
    Recommendation\ P.12 used to require certain articulation
values to be satisfied but the method is now mainly used for
diagnostic purposes. See Recommendation\ P.45.
.LP
    c)
    Various Questions, for example Question 4/XII [11],
Question\ 14/XII\ [12] and Supplement\ No.\ 3 at the end of this
fascicle.
.LP
    d)
    Various Questions, for example Question 4/XII [11],
Question\ 9/XII\ [13], Ques
tion\ 14/XII\ [12] and
Supplement\ No.\ 3 at the end of this fascicle.
.LP
    e)
    Various Questions, for example Question\ 9/XII\ [13] and
References\ [14], [15] and\ [16].
.sp 2P
.LP
\fB5\fR     \fBGeneral comments on subjective methods used in the laboratory\fR
.sp 1P
.RT
.PP
\fR More detailed information on the conduct of subjective tests and interpretation
of their results are given in Recommendation\ P.74 and
Reference\ [2]. A rather broad survey of the relationship between various
methods is given in Reference\ [17].
.PP
When used to provide information to assist in transmission planning
of telephone networks, subjective methods should be employed with the following
considerations in mind:
.RT
.LP
    a)
    A clear description must be available of the type of
telephone connections to which the results are to be applied.
This is provided by formulating appropriate hypothetical
reference connections (HRCs) (see Recommendation\ G.103\ [7]).
.LP
    b)
    The levels, transmission losses, sending and receiving
reference equivalents,\ etc., of the HRCs must guide the
establishment of laboratory arrangements and the conduct of the
tests. Speech spectra and levels must be properly chosen to
correspond to those at the various points in the\ HRC.
.LP
    c)
    Subjects must be drawn from an appropriate population.
For example, if audiograms are obtained from subjects
participating in a conversation experiment, this information
should not be used to reject any subjects, because the resultant
bias in the sample would make the conclusions applicable only to
users with a certain range of hearing sensitivity. For this
reason it is safest to collect auxiliary information of this
type only after the subjects have finished their main task.
.LP
    d)
    Subjects must be treated within the experiments so that
the results obtained are valid for the desired applications.
This is the reason for taking the precautions described
above (\(sc\ 3.3.1) to ensure that subjects' judgements are not
distorted by the range of conditions and levels chosen, or by
the order of presentation; and to make the procedure in
conversation tests (\(sc\(sc\ 3.4.1.5 to\ 3.4.1.7) natural yet
standardized.
.LP
    e)
    Suitable experimental designs must be used so that the
results can be properly analyzed and confidence intervals
estimated.
.LP
    f
)
    Uncontrolled variation in some feature of the
transmission path is sometimes unavoidable: for example the
requirement may be to conduct a listening test over a fading
radio link, or a conversation test over a TASI link with
freeze\(hyout determined by real traffic. In such cases it is
advisable to collect not only the subjects' responses but also
contemporary information on the values of the related
fluctuating quantities: signal strength in the first case,
freeze\(hyout fraction or number of channels occupied in the
second. The technique known as analysis of covariance
(Reference\ [18]) is the appropriate method for processing this
information on concomitant variables, as they are called, in
conjunction with the responses (main variables).
.bp
.LP
    g)
    Even with proper precautions under c), d), e) and f),
reliance should not be placed on absolute values of scores
unless \*Qcontrol\*U conditions (e.g.\ a set of reference conditions)
are included within the experiment. However, relativities
between scores obtained from different circuit conditions within
the same experiment are more reliable.
.LP
    h)
    A set of reference conditions will make it possible
to express results as ratings in terms of equivalent settings
of some reference device\ \(em attenuator, noise source, modulated
noise reference unit (see Recommendation\ P.81),\ etc. This
enables much more reliable comparisons to be made with
information from other sources.
.LP
    i)
    Results of subjective experiments should always be
reviewed for internal consistency and compared with expected
results (derived from previous experience or from a theoretical
model) before being applied.
.sp 2P
.LP
\fB6\fR     \fBObjective methods\fR
.sp 1P
.RT
.PP
Clearly the ultimate aim must be to attain the capability of
assessing telephony transmission performance purely in terms of the objective
characteristics of the telephone connections concerned. This aim is partly
satisfied by use of tabulated information based on previous laboratory and
other tests: an example of such usage appears in Reference\ [19].
Considerable progress has now been made towards the prediction of assessment
scores, speech levels,\ etc. by use of subjective modelling as described in
Supplement\ No.\ 3 at the end of this fascicle and Reference\ [20]. British
Telecom is now updating its tabulated information using this method.
.PP
\fR The modelling technique makes it possible to treat many other
important features like attenuation/frequency distortion and sidetone in
a much more general manner. For example, by making due allowance for the
part played by high sidetone level\ \(em which is a very potent degradation
in connections of poor transmission performance\ \(em it makes clear why
sensible limits for
overall loss and noise cannot be fixed without regard to sidetone
suppression.
.RT
.ce 1000
ANNEX\ A
.ce 0
.ce 1000
(to Supplement No. 2)
.sp 9p
.RT
.ce 0
.ce 1000
\fBOpinion form 12A\fR
.sp 1P
.RT
.ce 0
.LP
Test\
.sp 1P
.RT
.ad r
Name
\
Cabinet\
No.\
.sp 9p
.RT
.ad b
.RT
.sp 2P
.LP
1
    Before starting your call, please take out picture set\
and
arrange the cards in order of preference. Record this order in the boxes
below, using the numbers on the backs of the cards for identification.
.sp 1P
.RT
.LP
.ce
\fBH.T. [T1.2]\fR
.T&
lw(48p) | lw(30p) | lw(30p) | lw(30p) | lw(30p) | lw(30p) | lw(30p) , ^
| l | l | l | l | l | l.


.T&
lw(48p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) , ^
| l | l | l | l | l | l.
Your Order of Preference    1st    2nd    3rd    4th    5th    6th

_
.TE
.nr PS 9
.RT
.ad r
\fBTable A\(hy1 [T1.2], p. \fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
2
    If you receive a green GO AHEAD signal, then call your partner
on\
. Otherwise wait for your partner to call you.
.bp
.sp 9p
.RT
.sp 1P
.LP
3
     You may enter your partner's picture\(hycard order here if you find this
helps you in the discussion.
.sp 9p
.RT
.ce
\fBH.T. [T2.2]\fR
.T&
lw(48p) | lw(30p) | lw(30p) | lw(30p) | lw(30p) | lw(30p) | lw(30p) , ^
| l | l | l | l | l | l.


.T&
lw(48p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) , ^
| l | l | l | l | l | l.
Partner's Order of Preference    1st    2nd    3rd    4th    5th    6th

_
.TE
.nr PS 9
.RT
.ad r
\fBTable A\(hy2 [T2.2], p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
4
    When you have arrived at an agreed order of preference, please
enter it here.
.sp 9p
.RT
.ce
\fBH.T. [T3.2]\fR
.T&
lw(48p) | lw(30p) | lw(30p) | lw(30p) | lw(30p) | lw(30p) | lw(30p) , ^
| l | l | l | l | l | l.


.T&
lw(48p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) , ^
| l | l | l | l | l | l.
Agreed Order of Preference    1st    2nd    3rd    4th    5th    6th

_
.TE
.nr PS 9
.RT
.ad r
\fBTable A\(hy3 [T3.2], p. \fR
.sp 1P
.RT
.ad b
.RT
.LP
    Then replace your handset.
.sp 1P
.LP
5
     Please mark, with a cross, your opinion of the telephone connection you
have just been using. \fIN.B.\fR \ \(em\ Please do not discuss your opinion
with your
partner.
.sp 9p
.RT
.ce
\fBH.T. [T4.2]\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(36p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
Excellent    Good    Fair    Poor    Bad
_
.TE
.nr PS 9
.RT
.ad r
\fBTable A\(hy4 [T4.2], p. \fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
6
     Did you or your partner have any difficulty in talking or hearing over
the connection?
.sp 9p
.RT
.ce
\fBH.T. [T5.2]\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(36p) | lw(36p) .
YES
_
.T&
cw(36p) | lw(36p) .
NO
_
.TE
.nr PS 9
.RT
.ad r
\fBTable A\(hy5 [T5.2], p. \fR
.sp 1P
.RT
.ad b
.RT
.LP
    If the answer is YES, please explain briefly what the difficulty
was when the operator contacts you again.
.ce
\fBH.T. [T6.2]\fR
.T&
lw(60p) | lw(12p) | lw(12p) | lw(12p) | lw(12p) | lw(12p) | lw(12p) | lw(12p)
| lw(12p) | lw(12p) | lw(12p) | lw(12p) | lw(12p) | lw(12p) | lw(12p) .

.T&
lw(60p) | lw(12p) | lw(12p) | lw(12p) | lw(12p) | lw(12p) | lw(12p) | lw(12p)
| lw(12p) | lw(12p) | lw(12p) | lw(12p) | lw(12p) | lw(12p) | lw(12p) .
FOR R13.4 USE
_
.TE
.nr PS 9
.RT
.ad r
\fBTableau A\(hy6 [T6.2], p. \fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.ce 1000
ANNEX\ B
.ce 0
.ce 1000
(to Supplement No. 2)
.sp 9p
.RT
.ce 0
.ce 1000
\fB(Standard letter sent to subjects)\fR
.sp 1P
.RT
.ce 0
.LP
Name\
.sp 1P
.RT
.sp 1P
.LP
Group\
.sp 9p
.RT
.sp 1P
.LP
R13.4 SUBJECTIVE TEST No.\
.sp 9p
.RT
.PP
Thank you for agreeing to take part in this experiment.
.PP
As arranged earlier by telephone, we should like you to come to
Room\
, Floor 3, Main Laboratory Block, at the following
times.
.RT
.LP
    Time
Day
Date
\v'6p'
.PP
On arrival, ask for
, quoting the above subjective test number. You will be reminded by telephone
shortly before each visit is
due. You may book your time to project
. If you cannot keep an
appointment, or if you need further information, contact
on
Ipswich\ 64\
.
.PP
The experiment to which you have been invited forms part of a series
concerned with the transmission performance of telephone connections. You
will be asked to converse with another volunteer over particular telephone
connections, and it is hoped that the tasks we shall give you will lead to
vigorous conversations devoted to discussion and negotiation.
.PP
In the test room you will be provided with a set of six picture cards.
You are asked to imagine that you and your partner are responsible for
choosing some of these (enlarged if necessary) to be displayed in a public
place such as the Staff Restaurant\ \(em either as items of general interest
or simply as
decoration. Before each call you should arrange all six cards in your order
of preference, and write the six identification numbers in this order on
the form provided. Your partner, in another room, will have an identical
set of
pictures, and his order of preference will probably be different from yours.
One of you will then be requested to make a telephone call to the other. The
aim of the ensuing conversation will be to negotiate with your partner
so as to arrive at a compromise order which satisfies you both. At the
end of the
conversation you should replace the handset and enter the six numbers in the
finally agreed order on the form. You must also mark the appropriate box to
indicate your opinion of the connection. After this the operator will contact
you and tell you what to do next. Subsequent conversations will be similar,
but with different sets of pictures.
.PP
In the whole experiment there will be a total of\
\ calls spread over the\
\ visit(s) arranged as above. Full instructions will be given when you
arrive. Please bring this letter with you, and also your glasses if
you normally wear any.
.PP
Thank you once again for your co\(hyoperation.
\v'6p'
.RT
.ad r
\ (date)
.vs +6p
.RT
.ad b
.RT
.ad r
\ (date)
.ad b
.RT
.sp 2P
.LP
    \fBReferences\fR
.sp 1P
.RT
.LP
[1]
    CCITT\ \(em\ Question 15/XII, Contribution COM XII\(hyNo. 1, Study Period
1981\(hy1984, Geneva,\ 1981.
.LP
[2]
    RICHARDS (D. | .): Telecommunication by speech, \fIButterworths\fR ,
London,\ 1973.
.LP
[3]
     SULLIVAN (J. | .): Is transmission satisfactory? Telephone customers
help us decide, \fIBell Labs Record\fR , pp.\ 90\(hy98, March\ 1974.
.LP
[4]
     RICHARDS (D. | .): Telecommunications by speech, \(sc\ 3.5.3. \fIButterworths\fR
, London,\ 1973.
.LP
[5]
    \fIIbid.\fR , \(sc\ 4.5.1.
.bp
.LP
[6]
    CCITT Recommendation \fIThe transmission plan\fR , Vol.\ III, Rec.\ G.101.
.LP
[7]
    CCITT Recommendation \fIHypothetical reference connections\fR , Vol.\ III,
Rec.\ G.103.
.LP
[8]
    CCITT Recommendation \fILoudness ratings (LRs) in an international\fR
\fIconnection\fR , Vol.\ III, Rec.\ G.111.
.LP
[9]
    CCITT Recommendation \fITransmission characteristics of national\fR
\fInetworks\fR , Vol.\ III, Rec.\ G.120.
.LP
[10]
    CCITT Recommendation \fILoudness ratings (LRs) of national systems\fR ,
Vol.\ III, Rec.\ G.121.
.LP
[11]
    CCITT\ \(em\ Question 4/XII, Contribution COM XII\(hyNo.\ 1, Study Period
1985\(hy1988, Geneva,\ 1985.
.LP
[12]
    CCITT\ \(em\ Question 14/XII, Contribution COM XII\(hyNo.\ 1, Study Period
1985\(hy1988, Geneva,\ 1985.
.LP
[13]
    CCITT\ \(em\ Question 9/XII, Contribution COM XII\(hyNo.\ 1, Study Period
1981\(hy1984, Geneva,\ 1981.
.LP
[14]
    RICHARDS (D. | .) and BUCK (G. | .): Telephone echo tests, \fIP.I.E.E.\fR ,
107B, pp.\ 553\(hy556,\ 1960.
.LP
[15]
    CCITT\ \(em\ Contribution COM XII\(hyNo.\ 171, Study Period 1977\(hy1980,
Geneva,\ 1979.
.LP
[16]
    CCITT\ \(em\ Contribution COM XII\(hyNo.\ 132, Study Period 1977\(hy1980,
Geneva,\ 1979.
.LP
[17]
    CCITT\ \(em\ Question 7/XII, Annex\ 1, Contribution COM XII\(hyNo.\ 1, Study
Period 1981\(hy1984, Geneva,\ 1981.
.LP
[18]
     SNEDECOR (G. | .) and COCHRAN (W. | .): Statistical methods, Chapter\
14, 6th edition, \fIIowa State University Press\fR , 1967.
.LP
[19]
    CCITT\ \(em\ Contribution COM XII\(hyNo.\ 173, Study Period
1977\(hy1980, Geneva, 1979.
.LP
[20]
    RICHARDS (D. | .): Calculation of opinion scores for telephone
connections, \fIProc. IEE\fR , 121, pp.\ 313\(hy323,\ 1974.
.sp 2P
.LP
    \fBBibliography\fR
.sp 1P
.RT
.LP
BRAUN (K.): Die Bezugsd\*:ampfung und ihre Berechnung aus der
Restd\*:ampfungskurve (Frequenzkurve) eines \*:Ubertragungssystems;
\fIT.F.T.\fR , Vol.\ 28, pp.\ 311\(hy318, August\ 1939.
.LP
BRAUN (K.): Theoretische und experimentelle Untersuchung der
Bezugsd\*:ampfung und der Lautst\*:arke; \fIT.F.T.\fR , Vol.\ 29,
pp.\ 31\(hy37, No.\ 2, 1940.
.LP
BLYE (P. | .), COOLIDGE (O. | .) and HUNTLEY (H. | .): A revised
telephone transmission rating plan; \fIB.S.T.J.\fR , Vol.\ 34,
pp.\ 453\(hy472, May\ 1955 (reproduced in the \fIRed\ Book\fR , Vol.\ I,\fR
pp.\ 636\(hy651, ITU, Geneva,\ 1957, and Vol.\ V, pp.\ 607\(hy624, ITU,
Geneva,\ 1962).
.LP
BRAUN (K.): Image attenuations of microphone and receiver insets;
\fIN.T.Z.\fR , No.\ 8, pp.\ 365\(hy370, 1960 (translated in the \fIRed\
Book\fR ,
Vol.\ V | fIbis\fR , pp.\ 255\(hy265, ITU, Geneva,\ 1965).
.LP
FRENCH (N. | .) and STEINBERG (J. | .): Factors governing the
intelligibility of speech sounds; \fIJ.A.S.A.\fR , Vol.\ 19, p.\ 89,
Jan.\ 1947.
.LP
RICHARDS (D. | .) and ARCHBOLD (R. | .): A development of the Collard
principle of articulation calculation; \fIP.I.E.E.\fR , Vol.\ 103, Part\ B,
Sept.\ 1956 (\fIRed\ Book\fR , Vol.\ I, Question\ 7 of Study Group\ 12,
Annex\ 4, ITU,
Geneva,\ 1956).
.LP
Contribution by the Italian Administration to the study of objective
methods for measuring reference equivalent and articulation reference
equivalent, \fIRed\ Book\fR , Vol.\ I, Question\ 7 of Study Group\ 12,
Annex\ 3, ITU,
Geneva,\ 1956.
.LP
FLETCHER (H.) and GALT (R. | .): The perception of speech and its
relation to telephony; \fIJ.A.S.A.\fR , Vol.\ 22, p.\ 89, March\ 1950
(reproduced in the following work, Chapters\ 15\(hy17).
.LP
FLETCHER (H.): Speech and hearing in communication, \fID. Van\fR \fINostrand\fR
, New York,\ 1953.
.LP
Tonality method studied by the U.S.S.R. Administration to determine
articulation; \fIRed\ Book\fR , Vol.\ V, Part\ II, Annex\ 31, ITU, Geneva,\
1962.
.LP
Method used by the Swiss Telephone Administration for the determination
of transmission quality based on objective measurements; \fIRed\ Book\fR ,
Vol.\ V, Part\ II, Annex\ 30, ITU, Geneva,\ 1962.
.LP
LALOU (J.): Calculation of telephone transmission performance by
information theory, \fIRed\ Book\fR , Vol.\ V | fIbis\fR , Question\ 7/XII,
Annex\ 2, ITU,
Geneva,\ 1965.
.bp
.LP
SIVIAN (L. | .): Speech power and its measurement,
\fIB.S.T.J.\fR , 8, pp.\ 646\(hy661,\ 1929.
.LP
LOYE (D. | .) and MORGAN (K. | .): Sound picture recording and
reproducing characteristics, \fIJ. Soc. Motion Picture Engineers\fR ,
32, pp.\ 631\(hy647, 1939.
.LP
RICHARDS (D. | .): Some aspects of the behaviour of telephone users
as affected by the physical properties of the circuit. Communication
Theory, \fIButterworths Scientific Publications\fR , pp.\ 442\(hy449,\ 1953.
.LP
ZAITSEV (T. | .): Correlation method for determining the fidelity and
intelligibility of speech transmitted over telecommunication channels,
\fIElektrosvyaz\fR , 10, pp.\ 38\(hy46, 1958.
.LP
LICKLIDER (J. | . | .), BISBERG (A.) and SCHWARZLANDER (H.): An
electronic device to measure the intelligibility of speech, \fIProc. Nat.\fR
\fIElectronics Conf.\fR , 15, pp.\ 329\(hy334, 1959.
.LP
RICHARDS (D. | .) and SWAFFIELD (J.): Assessment of speech
communication links, \fIP.I.E.E.\fR , 106B, pp.\ 77\(hy89,\ 1959.
.LP
RICHARDS (D. | .): Conversation performance of speech links subject
to long propagation times, International Conference on Satellite
Communication, \fIInst. Elec. Engrs.\fR , pp.\ 247\(hy251, London,\ 1962.
.LP
RICHARDS (D. | .): Transmission performance of telephone connections
having long propagation times, \fIHet PTT\(hyBedrijf\fR , 15,
pp.\ 12\(hy24, 1967.
.LP
BOERYD, (A.): Subscriber reaction due to unbalanced transmission
levels, \fIibid\fR , pp.\ 39\(hy43.
.LP
RICHARDS, (D. | .): Distortion of speech by quantizing,
\fIElectronics Letters\fR , 3, pp.\ 230\(hy231,\ 1967.
.LP
GOLDMAN\(hyEISLER (F.): Sequential temporal patterns and cognitive
processes in speech, \fILanguage and Speech\fR , 10, pp.\ 122\(hy132, 1967.
\v'6p'
.sp 2P
.LP
\fBSupplement\ No.\ 3\fR
.RT
.sp 2P
.ce 1000
\fBMODELS\ FOR\ PREDICTING\ TRANSMISSION\ QUALITY\ FROM\fR
.EF '%    Volume\ V\ \(em\ Suppl.\ No.\ 3''
.OF '''Volume\ V\ \(em\ Suppl.\ No.\ 3    %'
.ce 0
.sp 1P
.ce 1000
\fBOBJECTIVE\ MEASUREMENTS\fR
.ce 0
.sp 1P
.PP
Models for predicting the subjective opinion of telephone
connections, using data from objective measurements, are currently under
study in Question\ 7/XII. It has not been possible up to now to recommend
a single
model applicable over a wide range of transmission impairments, but the
methods described in \(sc\(sc\ 1, 2, 3, 4\ below have been proposed by
several
Administrations.
.sp 1P
.RT
.sp 2P
.LP
\fB1\fR \fBTransmission rating models\fR \fI(Geneva, 1980; modified at\fR
\fIMalaga\(hyTorremolinos,\ 1984) (Quoted in \(sc\ 3 of Recommendation\
P.11)\fR
(Contribution by the Bell Communications Research, Inc.
.FS
This Section
(former Supplement\ No.\ 3, \fIRed Book\fR ), reflects in part work performed
at AT&T Bell Laboratories prior to 1\ January\ 1984.
.FE
)
.sp 1P
.RT
.sp 1P
.LP
1.1
    \fIIntroduction\fR
.sp 9p
.RT
.PP
This Section describes transmission rating models which can be
used to estimate the subjective reaction of telephone customers to the
transmission impairments of circuit noise, overall loudness rating, talker
echo, listener echo, attenuation distortion (including bandwidth), quantizing
distortion, room noise and sidetone.
.PP
The models for circuit noise overall loudness rating (OLR) and
talker echo are based on several conversational tests conducted at Bell
Laboratories in the period from\ 1965 to\ 1972 to evaluate the subjective
assessment of transmission quality as a function of circuit noise, overall
loudness rating, talker echo path loss and talker echo path delay\ [1]. These
tests involved several hundred subjects and several thousand test calls,
Several tests were conducted on normal business calls. Others were conducted
in the laboratory. All of the tests employed a 5\(hycategory rating scale:
excellent, good, fair, poor and unsatisfactory.
.bp
.PP
The essential features of the models were originally derived in terms of
loudness loss of an overall connection \fIin dB\fR (as measured by the
Electro\(hyAcoustic Rating System, \fIEARS\fR ) and circuit noise \fIin
dBmp\fR at the input to a reference receiving system (electric\(hyto\(hyacoustic
efficiency as measured by the \fIEARS\fR )\ [2]. The effects of talker
echo were later
incorporated in terms of loudness loss of the echo path \fIin dB\fR (as
measured by the \fIEARS\fR ) and round trip delay of the echo path \fIin
milliseconds\fR .
Experimentally determined correction factors were used to convert the models
to loudness ratings according to Recommendation\ P.79.
.PP
The original model for listener echo was based on a series of four
listening\(hytype subjective tests conducted at Bell Laboratories in\ 1977 and
1978\ [4]. Subsequent test results led to an alternative form of the model\
[5], [6]. The subjective tests included conditions in which the listener
echo path loss was flat or frequency\(hyshaped by selective filtering.
A weighted echo path loss is defined to provide a weighting of the frequency\(hyshaped
test conditions so that subjectively equivalent test conditions have the
same transmission
rating.
.PP
The model for quantizing distortion is based on a series of five
subjective tests conducted to evaluate the performance of
various digital codec algorithms [7], [8],\ [9].
.PP
The model for bandwidth and attenuation distortion is based on tests conducted
in\ 1978\ [10].
.PP
The model for room noise is based on unpublished tests conducted in
1976. Opinion ratings of transmission quality on a five\(hycategory scale were
made by 40\ subjects for 156\ conditions having various combinations of room
noise, speech level, circuit noise and sidetone path loss. The samples
of room noise were presented from tape recordings made in an airlines reservations
office. A model was fitted to the test results in terms of the circuit noise
which produced the same quality ratings as given levels of room noise.
.PP
The model for sidetone is based on tests conducted in 1980 [11].
.PP
All of the tests were conducted with Western Electric 500\(hytype telephone
sets or equivalent. The procedures used in the analysis of the subjective
tests results and the derivation of the transmission rating scale are outlined
in
Reference\ [1]. Although the procedures are somewhat complex for manual
calculation, they are easily handled on a digital computer and have been
found to provide a convenient and useful representation for a large variety
of test data.
.PP
The models incorporate the concept of a
transmission rating
scale
. An important reason for the introduction of this scale was the
recognition that subjective test results can be affected by various factors
such as the subject group, the type of test, and the range of conditions
which are included in the test. These factors have been found to cause
changes in
both the mean opinion score of a given condition and in the standard deviation.
Thus, there are difficulties in trying to establish a unique relationship
.PP
between a given transmission condition and subjective opinion in terms
of mean opinion score or percent of ratings which are good or excellent.
The
introduction of a transmission rating scale tends to reduce this difficulty
by separating the relationship between transmission characteristics and
opinion
ratings into two parts. The first part, the transmission rating as a function
of the transmission characteristic, is anchored at two points and tends
to be much less dependent on individual tests. The second part, the relationship
between the transmission rating and subjective opinion ratings, can then be
displayed for each individual test.
.PP
The transmission rating scale for overall loudness rating and circuit noise
was derived such that it is anchored at two points as shown in
Table\ 1\(hy1.
.RT
.ce
\fBH.T. [T1.3]\fR
.ce
TABLE\ 1\(hy1
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(60p) | cw(60p) | cw(60p) .
Overall loudness rating  (dB)     {
Circuit noise
(dBmp) | ua\d\u)\d
 }    Transmission rating
_
.T&
cw(60p) | cw(60p) | cw(60p) .
16    \(em61    80
.T&
cw(60p) | cw(60p) | cw(60p) .
31    \(em76    40
.TE
.LP
\ua\d\u)\d
The circuit noise values are referred to a receiving system with a receiving loudness rating (RLR)\ =\ 0\ dB.
.nr PS 9
.RT
.ad r
\fBTable 1\(hy1 [T1.3],\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
These anchor points were selected to be well separated but within the range
of conditions which are likely to be included in a test. The rating values
are such that most connections will have positive ratings between\ 40
and\ 100. Transmission ratings for other combinations of loudness rating and
circuit noise are relative to those for these two anchor points.
.PP
This Section presents the
transmission rating models
in terms of overall loudness rating of an overall connection in dB, circuit
noise in
dBmp referred to the input of a receiving system with a receiving loudness
rating (RLR)\ =\ 0\ dB, loudness rating of the talker echo path in\ dB, and
round\(hytrip delay of the talker echo path in milliseconds. Annex\ A illustrates
representative opinion results.
.RT
.sp 2P
.LP
1.2
    \fITransmission rating models\fR
.sp 1P
.RT
.sp 1P
.LP
1.2.1
    \fIOverall loudness rating and circuit noise\fR
.sp 9p
.RT
.PP
The transmission rating model for overall loudness rating and
circuit noise is
\v'6p'
.RT
.ce 1000
\fIR
\dLN
\u\fR = \(em26.76 \(em 2.257
@ sqrt { \fIL\fR~`~\fI~\de\u\fR~\(em~8.2) \u2\d~+~1 } @  \(em  2.0294 \fIN\fR `
\fI
\dF
\u\fR + 1.751 \fIL\fR `
\fI
\de\u\fR + 0.02037
\fIL\fR `
\fI
\de\u\fR \fIN\fR `
\fI
\dF
\u\fR
.ce 0
.ad r
(1\(hy1)
.ad b
.RT
.LP
.sp 1
.LP
where
.LP
    \fIL\fR `
\fI\fI\d\fIe\fR\u    is the OLR of an overall
telephone connection (in\ dB).
.LP
    \fIN\fR `
\fI\fI\d\fIF\fR\u is the total effective noise (in dBmp) referred to a
receiving system with a 0\ dB RLR. The total effective noise is obtained
by the power addition of the circuit noise, \fIN\fR `
\fI\fI\d\fIc\fR\u, the
circuit noise equivalent, \fIN\fR `
\fI\fI\d\fIR\fR\\d\fIe\fR\u, of the room noise and the circuit noise equivalent,
\fIN\fR `
\fI\fI\d\fIQ\fR\\d\fIe\fR\u, of the
quantizing noise.
.LP
    \fIN\fR `
\fI\fI\d\fIc\fR\u    is the circuit noise (in dBmp) referred to a
receiving system with a 0\ dB RLR.
.LP
    \fIN\fR `
\fI\fI\d\fIR\fR\\d\fIe\fR\u is the circuit noise equivalent (in dBmp) of
the room noise referred to a receiving system with a 0\ dB RLR. (See \(sc\
1.2.2.)
.LP
    \fIN\fR `
\fI\fI\d\fIQ\fR\\d\fIe\fR\u is the circuit noise equivalent (in dBmp) of
the quantizing noise referred to receiving system with a 0\ dB RLR. (See
\(sc\ 1.2.3.)
.PP
Transmission rating as a function of the OLR and circuit noise is shown
in Figure\ 1\(hy1. This figure uses a value of
\fIN\fR `
\fI\fI\d\fIR\fR\\d\fIe\fR\u\ =\ \(em58.63\ dBmp. Bandwidth factor, \fIk\fR\d\fIB\fR\\d\fIW\fR\u,
defined in \(sc\ 1.2.4 is equal to unity.
.sp 1P
.LP
1.2.2
    \fICircuit noise equivalent of the room noise\fR
.sp 9p
.RT
.PP
The transmission rating model for the circuit noise equivalent,
\fIN\fR `
\fI
\dRe
\u\fR \ (in\ dBmp), of the room noise is
\v'6p'
.RT
.ce 1000
\fIN\fR `
\fI
\dRe
\u\fR = \fIN
\dR\u\fR \(em 121 + 0.0078 (\fIN
\dR\u\fR \(em 35)
\u2\d
+ 10 log
\d10
\u
@ left [ 1~+~10~~\u { ~\(em~\fIL\fR~`~\fI~\ds\u\fR } over { 0 } \d right ] @
.ce 0
.ad r
(1\(hy2)
\v'7p'
.ad b
.RT
.LP
.sp 1
where
.LP
    \fIN\fR\d\fIR\fR\u    is the room noise in dB(A) at the listening end
.LP
    \fIL\fR `
\fI\fI\d\fIs\fR\u is the sidetone masking rating (in\ dB) of the listening
end telephone set sidetone path
.PP
The circuit noise equivalent, \fIN\fR `
\fI
\dRe
\u\fR ,  is plotted as a function of room noise in Figure\ 1\(hy2.
.PP
\fINote\fR \ \(em\ The transmission rating model for loudness rating and
circuit noise is normally used with
\v'6p'
.RT
.ce 1000
\fIN\fR `
\fI
\dRe
\u\fR = \(em58.63 dBmp.
.ce 0
.ad r
(1\(hy3)
.ad b
.RT
.PP
.sp 1
This value was determined from analysis of the conversational
tests results from which the transmission rating model for the overall
loudness rating and circuit noise was originally formulated.
.bp
.LP
.rs
.sp 24P
.ad r
\fBFigure\ 1\(hy1, p.
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 23P
.ad r
\fBFigure 1\(hy2, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
1.2.3
    \fICircuit noise equivalent of quantizing noise\fR
.sp 9p
.RT
.PP
The transmission rating model for the circuit noise equivalent
\fIN\fR `
\fI\fI\d\fIQ\fR\\d\fIe\fR\u(in dBmp) of quantizing noise is
\v'6p'
.RT
.ce 1000
\fIN\fR `
\fI\fI\d\fIQ\fR\\d\fIe\fR\u= \fIV\fR \ \(em\ 2\ \(em\ SNR
.ce 0
.ad r
(1\(hy4)
.ad b
.RT
.LP
.sp 1
where
.LP
    \fIV\fR     is the active speech level (in dBM) referred to a receiving
system with a 0\ dB RLR,
.LP
and
.LP
    SNR
    is the signal\(hyto\(hycircuit noise ratio (in\ dB) which is
judged to provide speech quality equivalent to the
speech\(hyto\(hyspeech correlated noise ratio, \fIQ\fR (in\ dB), as
determined by a Modulated Noise Reference Unit
(see Recommendation\ P.81).
.PP
SNR can be approximated by
\v'6p'
.ce 1000
SNR = 2.36 \fIQ\fR \ \(em\ 8
.ce 0
.ad r
(1\(hy5)
.ad b
.RT
.LP
.sp 1
from which
\v'6p'
.ce 1000
\fIN\fR `
\fI\fI\d\fIQ\fR\\d\fIe\fR\u= \fIV\fR \ \(em\ 2.36 \fIQ\fR \ +\ 6
.ce 0
.ad r
(1\(hy6)
.ad b
.RT
.PP
.sp 1
Based on a 1975\(hy1976 Speech Level Survey, [12] the speech level
for domestic North American connections can be approximated by
\v'6p'
.sp 1P
.ce 1000
\fIV\fR = \(em9 \(em\ \fIL\fR `
\fI\fI\d\fIe\fR\u
.ce 0
.sp 1P
.LP
.sp 1
from which
\v'6p'
.ce 1000
\fIN\fR `
\fI\fI\d\fIQ\fR\\d\fIe\fR\u= \(em3\ \(em\ \fIL\fR `
\fI\fI\d\fIe\fR\u\ \(em
2.36\ \fIQ\fR
.ce 0
.ad r
(1\(hy7)
.ad b
.RT
.LP
.sp 1
.PP
Estimates of \fIQ\fR  | or single codec pairs are given below for
Pulse Code Modulation (PCM), Nearly\(hyInstantaneous Compandored modulation
(NIC), Adaptive Differential Pulse Code Modulation (ADPCM) and Adaptive
Delta Modulation (ADM). They apply to the particular algorithms described
in References\ [7] and\ [9].
.ad r
    PCM:
    \fIQ\fR \ =\ 0.78\ \fIL\fR \ \(em\ 12.9
(1\(hy8)
.ad b
.RT
.ad r
        NIC:
    \fIQ\fR \ =\ 0.74\ \fIL\fR \ \(em\ \ 2.8
(1\(hy9)
.ad b
.RT
.ad r
        ADM:
    \fIQ\fR \ =\ 0.42\ \fIL\fR \ +\ \ 8.6
(1\(hy10)
.ad b
.RT
.ad r
    \fI\fR
    ADPCM:
    \fIQ\fR \ =\ 0.98\ \fIL\fR \ \(em\ \ 5.3
(1\(hy11)
.ad b
.RT
.ad r
        ADPCM\(hyV:
    \fIQ\fR \ =\ 1.04\ \fIL\fR \ \(em\ \ 4.6
(1\(hy12)
.ad b
.RT
.LP

where
.LP
    \fIL\fR     is the line bit rate in kbit/s.
.PP
\fINote\fR \ \(em\ The ADPCM algorithm with fixed predictor is described
in Reference\ [13]. The ADPCM\(hyV algorithm with adaptive predictor is
described in Reference\ [9].
.PP
For connections with tandem codec pairs, the total \fIQ\fR  | an be
estimated as follows:
\v'6p'
.RT
.ce 1000
\fIQ\fR = \(em15 log
\d10
\u
@ left [  pile { fIn\fR above sum above \fIi\fR~=1 } 10~\u\(em { fIQ~\di\u\fR } over { 5 } \d right ] @
.ce 0
.ad r
(1\(hy13)
\v'8p'
.ad b
.RT
.LP
.sp 1
.sp 1P
.LP
1.2.4
    \fIBandwidth and attenuation distortion\fR
.sp 9p
.RT
.PP
The transmission rating model for overall loudness rating and
circuit noise can be modified to include the effects of bandwidth (and
attenuation distortion). The transmission rating,
\fIR\fR \s6\fILNBW\fR .PS 10
, for overall loudness rating, circuit
noise and bandwidth is
\v'6p'
.RT
.ce 1000
\fIR\fR \s6\fILNBW\fR .PS 10
= (\fIR\fR\d\fIL\fR\\d\fIN\fR\u\ \(em\ 22.8)
\fIk\fR\d\fIB\fR\\d\fIW\fR\u\ +\ 22.8
.RT
.ce 0
.ad r
(1\(hy14)
.ad b
.RT
.LP
.sp 1
.bp
.LP
where
\v'6p'
.ad r
     \fIk\fR\d\fIB\fR\\d\fIW\fR\u\ =\ \fIk\fR\d1\u\fIk\fR\d2\u\fIk\fR\d3\u\fIk\fR\d4\u(1\(hy15)
.ad b
.RT
.LP
    .sp 1
.LP
with
\v'6p'
.ad r
    \fIk\fR\d1\u\ =\ 1\ \(em\ 0.00148 (\fIF\fR\d\fIl\fR\u\ \(em\ 310)
(1\(hy16)
.ad b
.RT
.ad r

    \fIk\fR\d2\u\ =\ 1\ +\ 0.000429 (\fIF\fR\d\fIu\fR\u\ \(em\ 3200)
(1\(hy17)
.ad b
.RT
.ad r

     \fIk\fR\d3\u\ =\ 1\ +\ 0.0372 (\fIS\fR\d\fIl\fR\u\ \(em\ 2)\ +\ 0.00215
(\fIS\fR\d\fIl\fR\u\ \(em\ 2)\u2\d
(1\(hy18)
.ad b
.RT
.ad r

     \fIk\fR\d4\u\ =\ 1\ +\ 0.0119 (\fIS\fR\d\fIu\fR\u\ \(em\ 3)\ \(em\ 0.000532
(\fIS\fR\d\fIu\fR\u
\(em\ 3)\u2\d \(em 0.00336\ (\fIS\fR\d\fIu\fR\u\(em 3)\ (\fIS\fR\d\fIl\fR\u\(em
2)
(1\(hy19)
.ad b
.RT
.LP

.sp 1
and
.LP
     \fIF\fR\d\fIl\fR\u, \fIF\fR\d\fIu\fR\u is the lower and upper band limits
(in Hz) at which the acoustic\(hyto\(hyacoustic response is 10\ dB lower
than the
response at 1000\ Hz. (For \fIF\fR\d\fIu\fR\u\ >\ 3200\ Hz, a value of
3200\ Hz should be used.)
.LP
     \fIS\fR\d\fIl\fR\u, \fIS\fR\d\fIu\fR\u is the lower and upper inband
response slopes (in dB/octave) below and above 1000\ Hz, respectively,
which would
have the same loudness loss as the actual response shapes.
.PP
Figures 1\(hy3 and 1\(hy4 illustrate the effect of the band limits,
\fIF\fR\d\fIl\fR\uand \fIF\fR\d\fIu\fR\u, and inband slopes, \fIS\fR\d\fIl\fR\uand
\fIS\fR\d\fIu\fR\u, on the bandwidth factor, \fIk\fR\d\fIB\fR\\d\fIW\fR\u.
.PP
\fINote\fR \ \(em\ The functions for the bandwidth factor, \fIk\fR\d\fIB\fR\\d\fIW\fR\u,
have been selected such that \fIk\fR\d\fIB\fR\\d\fIW\fR\u\ =\ 1 when \fIF\fR\d\fIl\fR\u\
=\ 310\ Hz,
\fIF\fR\d\fIu\fR\u\ =\ 3200\ Hz, \fIS\fR\d\fIl\fR\u\ =\ 2\ dB/octave and
\fIS\fR\d\fIu\fR\u\ =\ 3\ dB/octave. These
response characteristics are rep
resentative of those used in the tests to
formulate the transmission rating model for overall loudness rating and
circuit noise.
.RT
.LP
.rs
.sp 28P
.ad r
\fBFigure\ 1\(hy3, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 31P
.ad r
\fBFigure\ 1\(hy4, p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
1.2.5
    \fIListener echo\fR
.sp 9p
.RT
.PP
The transmission rating model for listener echo is
\v'6p'
.RT
.ce 1000
\fIR
\dLE
\u\fR = 9.3 (\fIWEPL\fR + 7) (\fID
\dL\u\fR \(em 0.4)
\u\(em0.229
\d
.ce 0
.ad r
(1\(hy20)
.ad b
.RT
.LP
.sp 1
where
.LP
    \fIWEPL\fR     is the Weighted Listener Echo Path Loss (in dB)
and
\v'6p'
.ce 1000
\fIWEPL\fR = \(em20 log
\d10
\u
[Unable to Convert Formula]
@ pile { 400 above int above 200 } @
10
\u\(em
@ { fIEPL\fR ( \fIf\fR ) } over { 0 } @
\d d
\fIf\fR
.ce 0
.ad r
(1\(hy21)
\v'1P'
\v'2p'
.ad b
.RT
.LP
.sp 1
.LP
    \fIEPL\fR (
\fIf\fR )
    is the echo path loss (in dB) as a
function of frequency in Hz.
.LP
    \fID\fR\d\fIL\fR\u    is the round\(hytrip listener echo path delay in
milliseconds.
.PP
Transmission rating, \fIR\fR\d\fIL\fR\\d\fIE\fR\u, as a function of the
weighted echo path loss and listener echo\(hypath delay is shown in
Figure\ 1\(hy5.
.bp
.LP
.rs
.sp 37P
.ad r
\fBFigure\ 1\(hy5, p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
The transmission rating for listener echo, \fIR\fR\d\fIL\fR\\d\fIE\fR\u,
can be combined with the transmission rating for overall loudness rating
and
circuit noise to give an overall transmission rating as follows:
\v'6p'
.ce 1000
\fIR
\dLNLE
\u\fR =
[Unable to Convert Formula]
[Unable to Convert Formula]
.ce 0
.ad r
(1\(hy22)
\v'7p'
.ad b
.RT
.PP
.sp 1
Figure 1\(hy6 provides curves generated by means of the above
relationship for transmission rating as a function of weighted listener echo
path loss and listener echo path delay in a connection with an overall
loudness rating of 16\ dB and a circuit noise of \(em56\ dBmp referred
to a RLR of
0\ dB.
.bp
.LP
.rs
.sp 27P
.ad r
\fBFigure\ 1\(hy6, p.
.sp 1P
.RT
.ad b
.RT
.PP
\fINote\fR \ \(em\ The preceding material is based on the use of a specific
set of test results and the listener echo model of Reference\ [4]. Subsequently,
new test results were reported in References\ [5] and\ [6] which also described
studies of the two sets of tests results to see if a single model could
be
recommended. In general, the agreement between the two sets of results was
good. However, the newer results had lower opinion ratings at delays less
than about 3\ ms. A conservative approach was to revise the original model
to
provide lower ratings at low delays while retaining the more critical
predictions at higher values of delay. The following equation (1\(hy20a)
provides a satisfactory replacement for equation (1\(hy20) which accomplishes
this
goal.
\v'6p'
.ce 1000
\fIR
\dLE
\u\fR = 10.5 (\fIWEPL\fR + 7) (\fID
\dL\u\fR + 1)
\u\(em0.25
\d
.ce 0
.ad r
(1\(hy20a)
.ad b
.RT
.LP
.sp 1
.PP
Reference [6] also proposed that Weighted Echo Path Loss (WEPL) in the
original model be replaced by Scaled Weighted Echo Path Loss (SWEPL). The
proposal defined
\v'6p'
.sp 1P
.ce 1000
\fIWEPL\fR = \fISM\fR + \fISF\fR
.ce 0
.sp 1P
.LP
.sp 1
where
.LP
    \fISM\fR     is the singing margin,
.LP
    \fISF\fR     is the shape factor
.LP
and then defined
\v'6p'
.sp 1P
.ce 1000
\fISWEPL\fR = \fISM\fR + \fISF\fR
@ { fISM\fR } over { ~+~\fISM\fR } @
.ce 0
.sp 1P
.LP
.sp 1
.bp
.LP
Hence, like \fIWEPL\fR ,
.LP
    \fISWEPL\fR \ =\ \fISM\fR , if \fISF\fR = 0.
.LP
Also,
.LP
    \fISWEPL\fR \ \( =\ \fIWEPL\fR , for \fISM\fR >> 1.
.PP
The effect of the shape factor is reduced as \fISM\fR  | pproaches
zero. Thus, the shape effect is cut in half when \fISM\fR is equal to unity,
and
approaches zero as \fISM\fR approaches zero. This avoids the possibility of a
positive \fISWEPL\fR when singing margin has become negative. Although
the use of \fISWEPL\fR instead of \fIWEPL\fR will cause little change in
most practical situations with typical values of \fISM\fR , the concept
is attractive in forcing the singing margin to be specifically taken into
account and is easily accomplished by
replacing \fIWEPL\fR by \fISWEPL\fR in equation (1\(hy20a).
.sp 1P
.LP
1.2.6
    \fITalker echo\fR
.sp 9p
.RT
.PP
The transmission rating model for talker echo is
\v'6p'
.RT
.ce 1000
\fIR
\dE\u\fR = 92.73 \(em 53.45 log
\d10
\u
@ left [ $$1o1~+~\fID\fR~$$2u sqrt { 1~+~ left ( { fID\fR } over { 80 } right ) $$2x2 } $$2e right ] @
+ 2.277 \fIE\fR
.ce 0
.ad r
(1\(hy23)
\v'2P'
.ad b
.RT
.LP
.sp 1
.LP
where
.LP
    \fIE\fR     is the OLR (in dB) of the talker echo path
.LP
    \fID\fR     is the round\(hytrip talker echo path delay in
milliseconds.
.PP
Transmission rating as a function of talker echo path loss and
delay is shown in Figure\ 1\(hy7 and has been derived to exclude the effects of
circuit noise and OLR. Transformation of the talker echo test results, which
included selected values of OLR and circuit noise, to the transmission
rating scale, was accomplished using the \fIR\fR\d\fIL\fR\\d\fIN\fR\umodel.
.PP
The transmission rating model for the combined effects of OLR,
circuit noise, echo path loss and echo path delay is
\v'6p'
.ce 1000
\fIR
\dLNE
\u\fR =
[Unable to Convert Formula]
[Unable to Convert Formula]
.ce 0
.ad r
(1\(hy24)
\v'7p'
.ad b
.RT
.PP
.sp 1
Figure 1\(hy8 shows curves generated by means of the above
relationship for the transmission rating as a function of talker echo path
loss and delay in a connection with an OLR of 16\ dB and circuit noise
of \(em56\ dBmp.
.sp 1P
.LP
1.2.7
    \fISidetone\fR
.sp 9p
.RT
.PP
The transmission rating model for OLR, total effective noise and
talker echo can be modified to include the effects of sidetone. The
transmission rating, \fIR\fR\d\fIL\fR\\d\fIN\fR\\d\fIS\fR\\d\fIT\fR\u,
for OLR, total
effective noise and sidetone is
\v'6p'
.EF '%    \fI\(''
.OF '''\fI\(    %'
.RT
.ce 1000
\fIR\fR\d\fIL\fR\\d\fIN\fR\\d\fIS\fR\\d\fIT\fR\u= \fIK\fR\d\fIS\fR\\d\fIT\fR\u\fIR\fR\d\fIL\fR\\d\fIN\fR\u
.EF '%    \fI\(''
.OF '''\fI\(    %'
.ce 0
.ad r
(1\(hy25)
.ad b
.RT
.LP
.sp 1
and for talker echo and sidetone is
\v'6p'
.ce 1000
\fIR\fR\d\fIE\fR\\d\fIS\fR\\d\fIT\fR\u= \fIR\fR\d\fIE\fR\u+ 2.6(12 \(em
\fISL\fR ) \(em\fR 1.5(4.5 \(em \fISR\fR )\u2\d + 3.38.
.EF '%    \fI\(''
.OF '''\fI\(    %'
.ce 0
.ad r
(1\(hy26)
.ad b
.RT
.LP
.sp 1
.LP
The sidetone factor, \fIK\fR\d\fIS\fR\\d\fIT\fR\u, is calculated from
\v'6p'
.ce 1000
\fIK\fR\d\fIS\fR\\d\fIT\fR\u= 1.021 \(em 0.002(\fISL\fR \(em 15)\u2\d +
0.001(\fISR\fR \(em 2)\u2\d
(\fISL\fR \(em 15).
.ce 0
.ad r
(1\(hy27)
.ad b
.RT
.LP
.sp 1
.bp
.LP
.rs
.sp 24P
.ad r
\fBFigura 1\(hy7, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 24P
.ad r
\fBFigura 1\(hy8, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
\fISL\fR  | s the sidetone masking rating (in dB), \fISR\fR  | s the
sidetone response (in dB/octave) below 1\ kHz. (The sidetone response above
1\ kHz is 1.5\ times greater.
.FS
    \fISidetone Response:\fR     \fIBelow 1 kHz\fR     \fIAbove 1 kHz\fR     \ 0
    \ 0
.PP
    +3.0
    +4.5
.PP
    +6.0
    +9.0
.FE
)
.PP
Figure 1\(hy9 shows curves obtained by determining
\fIR\fR\d\fIL\fR\\d\fIN\fR\\d\fIS\fR\\d\fIT\fR\u | and \fIR\fR\d\fIE\fR\\d\fIS\fR\\d\fIT\fR\u,
then substituting
these values for \fIR\fR\d\fIL\fR\\d\fIN\fR\uand \fIR\fR\d\fIE\fR\urespectively
in
equation\ (1\(hy24).
.EF '%    \fI\(''
.OF '''\fI\(    %'
.EF '%    \fI\(''
.OF '''\fI\(    %'
.RT
.sp 1P
.LP
1.3
    \fISubjective opinion models\fR
.sp 9p
.RT
.PP
Subjective opinion in terms of the proportion of ratings in each
of the five categories (E, G, F, P,\ U) for a condition having a given
transmission rating has been found to depend on various factors such as the
subject group, the range of conditions presented in a test, the year in
which the test was conducted, and whether the test was conducted on conversations
in a laboratory environment or on normal telephone calls. The proportion
of
comments Good plus Excellent (G\ +\ E) or Poor plus Unsatisfactory (P\
+\ U) can be computed from the following equations:
\v'6p'
.RT
.ce 1000
G + E =
[Unable to Convert Formula]
[Unable to Convert Formula]
\fIe\fR \u\(em
[Unable to Convert Formula]
\d d
\fIt\fR
.ce 0
.ad r
(1\(hy28)
\v'1P'
\v'2p'
.ad b
.RT
.ce 1000
.sp 1
P + U =
[Unable to Convert Formula]
@ pile { (em\(if above int above B } @
\fIe\fR \u\(em
[Unable to Convert Formula]
\d d
\fIt\fR
.ce 0
.ad r
(1\(hy29)
\v'1P'
\v'2p'
.ad b
.RT
.LP
.sp 1
where A and B are given below for data bases of primary interest.
.PP
For each data base listed below, the relationship between the
subjective judgements and transmission rating is shown in Figure\ 1\(hy10.
.LP
\fIData Base\fR
.FS
The three data bases reflect different relationships
between the transmission rating scale and opinion ratings as determined in
different tests as indicated below:
\fI1965 Murray Hill SIBYL Test\fR \ \(em\ Opinions on actual intra\(hybuilding
business calls.
\fICCITT Conversation Tests\fR \ \(em\ Composite model of opinion in laboratory
conversation tests reported to the CCITT
in the 1973\(hy1976 Study Period (see\ [3]).
\fILong Toll Interviews\fR \ \(em\ Opinions expressed by North American
Telephone
customers when interviewed following a call on a long toll
connection.
.FE
.LP
    \ \ \ \ \fIA\fR     \ \ \ \ \fIB\fR
.LP
1965 Murray Hill SIBYL Test
    (R\(hy64.07)/17.57
    (R\(hy51.87)/17.57
.LP
    CCITT Conversation Tests
    (R\(hy62)/15
    (R\(hy43)/15
.LP
    Long Toll Interviews
    (R\(hy51.5)/15.71
    (R\(hy40.98)/15.71
.LP
.sp 2P
.LP
\fB2\fR \fBPrediction of transmission qualities from objective measurements\fR
\fI(Geneva,\ 1980; modified in Malaga\(hy\fR
\fITorremolinos,\ 1984) (Quoted in\fR
\fIRecommendation\ P.11)\fR (Contribution from British Telecom)
.FS
Formerly,
Supplement\ No.\ 4, \fIRed Book\fR .
.FE
.sp 1P
.RT
.sp 1P
.LP
    \fISummary\fR
.sp 9p
.RT
.PP
British Telecom makes extensive use of a theoretical model for
predicting the
transmission performance of telephone connections
. A
brief description is here given of the structure of this model, and of the
computer program CATNAP, which embodies a simplified form of the model for
routine use, together with facilities for specifying connections in a
convenient practical way.
.bp
.RT
.LP
.rs
.sp 47P
.ad r
\fBFigure 1\(hy9, p. 16\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 27P
.ad r
\fBFigure\ 1\(hy10, p.17\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
2.1
    \fITypes of model\fR
.sp 9p
.RT
.PP
Question 7/XII [14] recognises two types of \*Qmodel\*U for predicting
the performance of complete telephone connections in conversation. The
first
kind, exemplified in Section\ 1 of this supplement, involves purely empirical
treatment of basic observations, and might lead to a set of tables, graphs
or relatively simple formulae, representing performance as a function of
certain objective quantities. In a model of this type, where attention
is focussed
entirely on the correspondence between input (objective quantities)
and output (subjective performance), the \fIform\fR of the functions employed
has no significance in itself. For convenience, simplicity is usually sought,
but is obtained at the expense of generality. Interactions between different
degradations are often difficult enough to treat in any case; but, besides,
a purely empirical model must usually be completely revised when a new
degradation is brought in. For example, suppose relationships have been
established between loss, noise and
opinion score
for one particular
bandwidth: changing that bandwidth to a new constant value will necessitate
a redetermination of the functions \(em not just a constant adjustment
of the
output. In short, it is unreasonable to expect that a purely empirical model
could have more than limited success in predicting performance.
.PP
Models of the second type (mentioned in [15]) are intended to overcome
these disadvantages by making the structure of the evaluation process reflect
the cause\(hyand\(hyeffect relationships which lead from the input (properties
of the connection; acoustic environment; characteristics of the participants'
hearing, speech sounds and language systems, etc.) to the output (participants'
satisfaction or estimate of performance). Such a model is inherently more
complicated, and requires more work to develop initially, but can then be
extended and applied with much greater ease and confidence. Numerical
parameters may and do require revision as more reliable data become available,
but the structure, if well chosen, will only rarely require major alterations.
As a research tool, such a model is much more powerful in its capability
of
generating hypotheses to be tested than a collection of useful but arbitrary
formulae. As a planning or application tool, it lends itself easily to being
embodied in a computer program, to which readily available data (such as
losses and line lengths) can be supplied as input.
.bp
.RT
.LP
.sp 1P
.LP
2.2
    \fIModel and programs: SUBMOD, CATPASS and CATNAP\fR
.sp 9p
.RT
.PP
The model here described is of the more fundamental type. It
is intended to predict loudness judgements, listening\(hyeffort scores,
conversation\(hyopinion scores and vocal levels from objective information
supplied. It is embodied in a program called SUBMOD (mnemonic for SUBJECTIVE
MODEL) which accepts the overall frequency responses of the speech\(hytransmission
paths as input, and makes provision for changing the parameters of the
model in order to improve agreement between theory and observation. Reference\
[16]
describes an earlier version of the same model.
.PP
In its present state of development the model deals fairly
successfully with the subjective effects of circuit loss,
attenuation\(hyfrequency distortion, circuit noise, quantizing noise, room
noise, and sidetone paths, for a reasonably wide range of values of these
characteristics in any combination. Effects of some other phenomena can
also be approximately estimated, but are not yet incorporated in the model.
No attempt has yet been made to cater for features such as voice\(hyswitching
effects, or
vocoding and other sophisticated schemes for reducing information rate.
Compare the groups of factors listed in Question\ 7/XII\ [14].
.PP
The program CATPASS [16] \(em a mnemonic for COMPUTER\(hyAIDED TELEPHONY
PERFORMANCE ASSESSMENT \(em incorporated the same model in a simplified,
fixed\(hyparameter implementation, together with facilities for calculating the
sensitivity\(hyfrequency response of a complete connection formed by concatenating
common pieces of apparatus such as telephones, cables, feeding bridges,
junctions, and filters. It was similar to the system described in\ [17]
and\ [18], but the program was differently organized. However, CATPASS could
handle symmetrical connections only \(em that is, those for which transmission,
room noise, sidetone and all other relevant features were the same for both
participants. It was superseded by a program called CATNAP (COMPUTER\(hyAIDED
TELEPHONE NETWORK ASSESSMENT PROGRAM), which incorporated an extended form
of the fixed\(hyparameter model, allowing asymmetry in the connections,
as well as
containing facilities for assembling performance statistics on sets of
connections. See\ [19].
.PP
CATNAP has been superseded in turn by CATNAP83, in which three main
changes have been made:
.RT
.LP
    a)
    minor improvements to the subjective model;
.LP
    b)
    calculation of loudness ratings according to
Recommendation\ P.79, instead of the provisional version P.XXE\ [20] which
(notwithstanding the statement made in the earlier version of this
Supplement\ [21]) was used for calculating loudness ratings in CATNAP;
.LP
    c)
     introduction of more flexibility to allow parameters such as the earphone
coupling loss factor (\fIL\fR\d\fIE\fR\u) to depend on the particular type
of handset.
.sp 1P
.LP
2.3
    \fISituation to be represented\fR
.sp 9p
.RT
.PP
Let A and B denote two \*Qaverage\*U participants in a telephone
conversation over a link terminated in handset telephones, located in rooms
with no abnormal reverberation and with specified levels of room noise.
\*QAverage\*U is intended to convey that the participants have representative
hearing and speaking characteristics and a normal attitude towards telephone
facilities, so that their satisfaction with the telecommunication link
may be measured by the
mean Conversation Opinion Score
(\fIY\fR\d\fIC\fR\u) and the
Percentage Difficulty
(%\fID\fR ) that would be obtained from a
conversation test, as described in Supplement\ No.\ 2. \fIY\fR\d\fIC\fR\ucan
take any value between\ 4 and\ 0, the scale being: 4\ =\ EXCELLENT, 3\
=\ GOOD, 2\ =\ FAIR, 1\ =\ POOR, 0\ =\ BAD. %\fID\fR can of course take
any value between 0 for the best connections and 100% for the worst.
.PP
For a given connection, the quantities of chief interest are
\fIY\fR\d\fIC\fR\u, %\fID\fR  | and the speech level, for each participant.
However, other useful auxiliary quantities are computed in the course of
the evaluation, such as the loudness ratings of the various paths (calculated
according to
Recommendation\ P.79), and \fIY\fR\d\fIL\fR\\d\fIE\fR\u, the mean
Listening Effort
Score
that would result from a listening opinion test conducted as outlined in\
Supplement\ No.\ 2. In a listening test of this type, lists of sentences
at a standard input speech level are transmitted over the connection and
the
listener expresses an opinion, at a number of different listening levels, on
the \*Qlistening effort\*U according to the following scale:
.RT
.LP
\fIEffort required to understand the meanings of sentences\fR
.LP
A
    Complete relaxation possible; no effort required
.LP
B
    Attention necessary; no appreciable effort required
.LP
C
    Moderate effort required
.LP
D
    Considerable effort required
.LP
E
    No meaning understood with any feasible effort.
.bp
.PP
The votes are scored A\ =\ 4, B\ =\ 3, C\ =\ 2, D\ =\ 1, E\ =\ 0, and
the mean taken over all listeners is called the Listening Effort Score,
\fIY\fR\d\fIL\fR\\d\fIE\fR\u, for each particular listening level and each
circuit
condition.
.PP
More detailed information about both conversation tests and listening tests
may be found in\ [22], and also in Supplement\ No.\ 2.
.RT
.sp 1P
.LP
2.4
    \fIOutline of the model\fR
.sp 9p
.RT
.PP
The model requires the following inputs:
.RT
.LP
    1)
    overall sensitivity\(hyfrequency characteristic of each
transmission path (talker's mouth to listener's ear via the
connection) and sidetone path (each talker's mouth to his own
ear). These sensitivities may be either measured by the method
described in Recommendation\ P.64 or calculated as explained in
Reference\ [17];
.LP
    2)
    noise spectrum and level at each listener's ear, composed
of noise arising in the circuit, room noise reaching the
listening ear direct, and room noise reaching the listening
ear via the sidetone path. In the absence of specific
measurements, standard noise spectra and levels are taken;
e.g.\ room noise with Hoth spectrum at 50\ dBA, circuit noise
with bandlimited spectrum at a specified psophometrically
weighted level;
.LP
    3)
    average speech spectrum and average threshold of hearing,
as given for example in\ [23].
.PP
From these data the
loudness ratings
are calculated. With speech level fixed, \fIY\fR\d\fIL\fR\\d\fIE\fR\u |
and a provisional value of \fIY\fR\d\fIC\fR\uare
evaluated for each participant. The relationships between \fIY\fR\d\fIC\fR\uand
speech
level at each end are then used to refine the values of both, so that the
final estimates represent performance at realistic conversational speech
levels.
.sp 1P
.LP
2.5
    \fICalculation of\fR
\fIloudness\fR \fIand\fR
\fIloudness\fR
\fIratings\fR
.sp 9p
.RT
.PP
The model starts by setting the speech level emitted from each
talker to a standard value and calculating the resultant spectrum and level
of both speech and noise at each listener's ear. The loudness of received
speech is calculated as a function of signal level, noise level and threshold
of
hearing, integrated over the frequency range extending normally from 179\ to
4472\ Hz (14\ bands, the lowest centred at 200\ Hz and the highest at 4000\
Hz).
The loudness of the sidetone speech is calculated similarly, but with an
allowance for the additional masking effect of speech reaching the ear
naturally (via the air path and the bone\(hyconduction path). By comparison
with the loudness of speech transmitted over an IRS (
Intermediate Reference
System
), the loudness ratings of the various paths are evaluated:
SLR
,
RLR
and
STMR
for each end, and
OLR
in each direction.
.PP
The method is described in [24], but is not given in detail here. The loudness
part of the model is important in its own right [for example in the
study of Question\ 19/XII\ [25]], but not closely connected with the rest
of the model. The program outputs loudness ratings calculated according
to
Recommendation\ P.79, but also calculates a set of loudness ratings according
to the earlier method\ [26] which are used for subsequent calculations.
.RT
.sp 1P
.LP
2.6
    \fICalculation of\fR
\fIlistening effort score\fR
.sp 9p
.RT
.PP
This part of the model is intended to reproduce the result that
would be obtained from a Listening Opinion Test.
.PP
It has been found possible to estimate \fIY\fR\d\fIL\fR\\d\fIE\fR\u | by
a process
similar to those already well known in calculating loudness and articulation
score. An intermediate quantity, Listening Opinion Index (LOI), is first
calculated as follows. Each elementary band in the frequency range contributes
to LOI an amount proportional to the product
\fIB\fR `
\fI\fI\d\fIf\fR\u\fIP\fR \ (\fIZ\fR\d\fIf\fR\u),
where \fIB\fR `
\fI\fI\d\fIf\fR\uis a frequency\(hyweighting factor expressing the
relative importance of that elementary
.bp
.PP
band for effortless
comprehension, and
\fIP\fR is a growth function applied to the sensation level\ \fIZ\fR (which
has already been evaluated for the loudness calculation). The actual values
of the
frequency\(hyweightings differ somewhat from those used in loudness and
articulation calculations; the growth function is limited to the range\
0 to\ 1 as in articulation, but the form used is:
\v'6p'
.RT
.sp 1P
.ce 1000
\fIP\fR (\fIZ\fR ) = 10
\u
@ { fIZ\fR~+~3.8 } over { 0 } @
\d\ \ if \fIZ\fR < \(em11,
.ce 0
.sp 1P
.ce 1000
.sp 1
\fIP\fR (\fIZ\fR ) = 1 \(em 10
\u
@ { (em0.3 (\fIZ\fR~+~14) } over { 0 } @
\d\ \ otherwise.
.ce 0
.sp 1P
.PP
.sp 1
LOI is proportional to
\s16\(is
\s9\fIB\fR `
\fI\d\fIf\fR\u\fIP\fR (\fIZ\fR\d\fIf\fR\u)
d
\fIf\fR , but in practice the integral is replaced by a summation over
a number of bands (normally 14), within each of which \fIZ\fR\d\fIf\fR\uand
\fIB\fR `
\fI\fI\d\fIf\fR\uare reasonably constant, just as in the loudness
evaluation. The formula actually used is:
\v'6p'
.RT
.sp 1P
.ce 1000
LOI = \fIAD\fR @ pile { sum above \fIi\fR } @\fIB\fR `
\fI
\di\u\fR \fIP\fR (\fIZ
\di\u\fR )
.ce 0
.sp 1P
.LP
.sp 1
.LP
where
.LP
    \fIB\fR `
\fI\fI\d\fIi\fR\u    is the frequency weighting for the
\fIi\fR th\ band, (shown diagrammatically in Figure\ 2\(hy1),
.LP
    \fIZ\fR\d\fIi\fR\u    is the mean \fIZ\fR \ in the \fIi\fR \ th band,
.LP
    \fIP\fR     is the appropriate growth function (illustrated in
Figure\ 2\(hy2),
.LP
    \fIA\fR     is a multiplier depending on the received speech level,
with the value\ 1 for a small range of levels around the optimum
but decreasing rapidly outside this range (see Figure\ 2\(hy3 where the zero
abscissa now corresponds to OLR = 8\ dB (Recommendation\ P.XXE\ [20]) instead
of 4\ dB as previously),
.LP
    \fID\fR     is a multiplier depending on the received noise level
(ICN\(hyRLR) with a value decreasing slowly from\ 1 at negligible
noise levels towards\ 0 at very high levels (see Figure\ 2\(hy4).
.LP
.rs
.sp 22P
.ad r
\fBFigure\ 2\(hy1, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 24P
.ad r
\fBFigure\ 2\(hy2, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 24P
.ad r
\fBFigure\ 2\(hy3, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 19P
.ad r
\fBFigure\ 2\(hy4, p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
Thus it is only for wide\(hyband, noise\(hyfree, distortion\(hyfree speech
at optimum listening level that LOI attains its maximum value of
unity.
.PP
The Listening Opinion Index is related to \fIY\fR\d\fIL\fR\\d\fIE\fR\u |
in a manner
which depends on the standard of transmission to which listeners have been
accustomed in their recent experience. It is found that the subjects' standard
of judgement is influenced mostly by the best circuit condition experienced
in the current experiment, or, in real calls, by the quality of the best
connections normally experienced. For example, a circuit condition which
earns a score of almost 4 in an experiment where it is the best condition,
would earn a score of perhaps only 3 if a practically perfect condition
were included in the same experiment, and about 3.5 if the best condition
in the same experiment were equivalent in performance to the best connection
that can normally occur in the British Telecom system. A parameter\ LOI
\s6LIM
.PS 10
,
introduced to cater for this effect, specifies the value of LOI that
corresponds to maximum \fIY\fR\d\fIL\fR\\d\fIE\fR\u; it is generally set
equal to 0.885
when connections are being judged against a background of experience with
the British Telecom network. The relationship in general terms is
\v'6p'
.RT
.sp 1P
.ce 1000
ln
@ left ( { fIY~\dLE~\u\fR } over { ~\(em~\fIY~\dLE~\u\fR } right ) @
= 1.465
@ left [ ln left ( { OI } over { OI~\dLIM~\u~\(em~LOI } right ) \(em~0.75~ right ] @
.ce 0
.sp 1P
.LP
.sp 1
as shown in Figure\ 2\(hy5. This brings us to the point where \fIY\fR\d\fIL\fR\\d\fIE\fR\u |
has been evaluated for each participant as a function of listening level\
\(em in
particular, at the listening level established for each participant when the
other speaks at Reference Vocal Level (RVL), defined in\ [27].
.sp 1P
.LP
2.7
    \fICalculation of\fR
\fIConversation Opinion Score\fR
.sp 9p
.RT
.PP
In order to convert a value of \fIY\fR\d\fIL\fR\\d\fIE\fR\u | at the appropriate
listening level to the corresponding value of Conversation Opinion Score
(\fIY\fR\d\fIC\fR\u), it is necessary to take account of deviations of
mean vocal
level from RVL.
.PP
The symbol \fIV\fR\d\fIL\fR\u | is used to denote the electrical speech
level in dBV at the output of a sending end when the acoustic level at
the input (mouth reference point) is RVL. During conversation, a different
level (\fIV\fR\d\fIC\fR\u) will generally prevail at the same point, because
participants tend to raise
their voices if incoming speech is faint or poor in quality and to lower
them if incoming speech is loud. In other words, \fIV\fR\d\fIC\fR\uat end\
\fIA\fR depends on
\fIY\fR\d\fIL\fR\\d\fIE\fR\uat end\ \fIA\fR , which depends on \fIV\fR\d\fIC\fR\uat
end B, which depends on
\fIY\fR\d\fIL\fR\\d\fIE\fR\uat end \fIB\fR , which depends in turn on \fIV\fR\d\fIC\fR\uat
end \fIA\fR . Thus there is a circular dependence or feedback effect.
.bp
.RT
.LP
.rs
.sp 21P
.ad r
\fBFigure\ 2\(hy5, p.\fR
.ad b
.RT
.PP
The sidetone paths introduce complications when STMR < | 3\ dB
(besides contributing noise from the environment to the receiving channel as
already explained). Other things being equal, each talker's vocal level goes
down by almost 1\ dB for every 3\ dB decrease in STMR below 13\ dB, and this of
course further modifies the opinion scores and speech levels at both ends by
virtue of the feedback effect.
.PP
In addition to this, very high sidetone levels are experienced as
unpleasant \fIper\ se\fR , particularly when the connection is poor for other
reasons.
.PP
This complex interrelationship is found to be reasonably well
represented by the following equations.
.RT
.LP
    \fIY\fR `
\fI
\dC\u\fR \ is an intermediate quantity explained
below.
\v'6p'
.ce 1000
ln
@ left ( { fIY\fR~`~\fI~\dC\u\fR } over { ~\(em~\fIY\fR~`~\fI~\dC\u\fR } right ) @
= 0.7
@ left [ ln left ( { fIY~\dLE~\u\fR } over { ~\(em~\fIY~\dLE~\u\fR } right ) ~+~0.5~\(em~ {  (13~\(em~STMR) } over { 0 } left ( { ~\(em~\fIY~\dLE~\u\fR } over { fIY~\dLE~\u\fR } right ) $$2x2 right ] @
.ce 0
.ad r
(2\(hy1)
\v'7p'
.ad b
.RT
.ce 1000
.sp 1
\fIV
\dC\u\fR \(em \fIV
\dL\u\fR = 4.0 \(em 2.1 \fIY\fR `
\fI
\dC\u\fR \(em 0.3 K (13 \(em STMR)
.ce 0
.ad r
(2\(hy2)
.ad b
.RT
.LP
.sp 1
.ce 1000
ln
@ left ( { fIY~\dC\u\fR } over { ~\(em~\fIY~\dC\u\fR } right ) @
= 0.8451
ln
@ left ( { fIY\fR~`~\fI~\dC\u\fR } over { ~\(em~\fIY\fR~`~\fI~\dC\u\fR } right ) @
\(em 0.2727
.ce 0
.ad r
(2\(hy3)
\v'7p'
.ad b
.RT
.LP
.sp 1
where
.LP
    K\ =\ 1 if STMR <\ 13,
.LP
    K\ =\ 0 otherwise.
.PP
By substituting in equation (2\(hy1) the value of \fIY\fR\d\fIL\fR\\d\fIE\fR\u |
already found for end\ A \(em which would apply for \fIV\fR\d\fIC\fR\u\
=\ \fIV\fR\d\fIL\fR\uat end B\ \(em
one obtains a first approximation to \fIY\fR `
\fI
\dC\u\fR , then from
equation\ (2\(hy2) an approximation to \fIV\fR\d\fIC\fR\uat end A. The
earlier calculations are repeated with this speech level to find a new
value of \fIY\fR\d\fIL\fR\\d\fIE\fR\uat
end\ B, hence an approximation to \fIY\fR `
\fI
\dC\u\fR and \fIV\fR\d\fIC\fR\uat end\ B. This
process is repeated cyclically until each \fIY\fR `
\fI
\dC\u\fR converges to a
settled value, and then equations (2\(hy1) and (2\(hy2) are simultaneously
satisfied.
.PP
Figure 2\(hy6 shows the form of the resultant relationship between
\fIY\fR\d\fIL\fR\\d\fIE\fR\u | and \fIY\fR `
\fI
\dC\u\fR ,  for two different values of STMR,
with \fIV\fR\d\fIC\fR\uat its proper value. The transformation [equation
(2\(hy3)],
illustrated in Figure\ 2\(hy7, is then applied to the intermediate score
\fIY\fR `
\fI
\dC\u\fR , to give the estimated Conversation Opinion Score
\fIY\fR\d\fIc\fR\u, which is shown as a function of \fIY\fR\d\fIL\fR\\d\fIE\fR\uin
Figure\ 2\(hy8.
.bp
.RT
.LP
.rs
.sp 24P
.ad r
\fBFigure 2\(hy6, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 24P
.ad r
\fBFigures 2\(hy7 and 2\(hy8, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
2.8
    \fIEvaluation of other subjective measures of performance\fR
.sp 9p
.RT
.PP
Relationships have been developed for various dichotomies of the
opinion scale \(em such as proportion of votes greater than\ 2 (i.e.\ votes
\*QExcellent\*U or \*QGood\*U) \(em and for the percentage of positive
replies to the
\*QDifficulty\*U question (Supplement\ No.\ 2).
.PP
For example, percentage \*QDifficulty\*U is represented by the
equation
\v'6p'
.RT
.sp 1P
.ce 1000
ln
@ left ( { fID\fR } over { ~\(em~\fID\fR } right ) @
= \(em2.3
ln
@ left ( { fIY~\dC\u\fR } over { ~\(em~\fIY~\dC\u\fR } right ) @
.ce 0
.sp 1P
.LP
.sp 1
where
.LP
    \fID\fR \ \(mu\ 100\ =\ %\fID\fR .
.PP
However, these relationships are satisfactory only for certain
kinds of degradation and are still under review.
.sp 1P
.LP
2.9
    \fICorrespondence between calculated and observed values\fR
.sp 9p
.RT
.PP
For symmetrical connections, provided very high sidetone levels and very
high room noise levels are excluded, the model reproduces fairly well
the results of laboratory conversation tests carried out in the U.K. In the
most recent laboratory tests there is a tendency for speech levels and hence
opinion scores to be somewhat lower than those observed earlier, but the
relativities between circuit conditions are not much disturbed by this.
It is believed, but not yet fully established, that approximately the same
relativities hold good for other populations of subjects \(em in particular,
for the population of ordinary telephone users accustomed to the British
Telecom
system \(em even though different absolute values of scores may be obtained
from other populations of subjects or by using different experimental
procedures.
.PP
Comparatively few results are available from experiments on
asymmetrical connections, but such evidence as there is indicates that the
model predicts too much divergence between the two ends of the connection \(em
especially in respect of \fIV\fR\d\fIC\fR\u, less so in respect of \fIY\fR\d\fIC\fR\u.
It is proposed to introduce a feedback feature to reduce the divergence
between
the two \fIV\fR\d\fIC\fR\uvalues, but care will be needed not to reduce
the \fIY\fR\d\fIC\fR\u
divergence too far as a result of this. HRC\ 4 in Annex\ A gives an example of
CATNAP calculations for a set of connections with asymmetrical losses:
compare these predictions with Reference\ [30] there quoted.
.PP
Predictions of \fIY\fR\d\fIC\fR\u | and \fIV\fR\d\fIC\fR\u | from both
CATNAP83 have been
compared with the results of a number of conversation experiments conducted
in the U.K. since\ 1976. The degree of agreement is summed up in
Table\ 2\(hy1.
.RT
.ce
\fBH.T. [T2.3]\fR
.ce
TABLE\ 2\(hy1
.ce
\fBComparison of observed (O) and predicted (P) results for two
.ce
models\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(36p) | cw(60p) | cw(36p) | cw(24p) sw(24p) sw(24p) sw(24p) , ^  | ^  | ^  | c s | c
^  | ^  | ^  | c | c | c | c.
Program    Types of connection    No. of conversations    Deviations (O\ \(em\ P)
            Mean    r.m.s.    \fIV\fI    \fIY\fI    \fIV\fI    \fIY\fI
_
.T&
cw(36p) | lw(60p) | cw(36p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) .
CATNAP\ \     Symmetrical only    680    \(em0.8    \(em0.29    4.1    0.41
.T&
cw(36p) | lw(60p) | cw(36p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) .
CATNAP\ \     Symmetrical and asymmetrical    883    \(em1.0    \(em0.22    3.8    0.38
.T&
cw(36p) | lw(60p) | cw(36p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) .
CATNAP83    Symmetrical only    680    \(em0.2    \(em0.02    4.0    0.26
.T&
cw(36p) | lw(60p) | cw(36p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) .
CATNAP83    Symmetrical and asymmetrical    883    \(em0.4    +0.14    3.8    0.44
_
.TE
.nr PS 9
.RT
.ad r
\fBTable 2\(hy1 [T2.3], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
It will be seen that the improvement in \fIY\fR\d\fIC\fR\u | as predicted
for symmetrical connections has been achieved at the cost of a slight increase
in the r.m.s. deviation of \fIY\fR\d\fIC\fR\uwhen asymmetrical connections
are included. But in view of the further alterations expected to be needed
for the adequate
prediction of the performance of asymmetrical connections, it is appropriate
at the present stage to be guided mainly by the results for symmetrical
connections.
.sp 2P
.LP
2.10
    \fIIncorporating miscellaneous degradations\fR
.sp 1P
.RT
.sp 1P
.LP
2.10.1
    \fIPCM quantizing distortion\fR
.sp 9p
.RT
.PP
Reference [28] describes a method for handling the effects of
quantizing distortion in PCM systems. It is there established that a
quantity\ \fIQ\fR , effective speech\(hyto\(hyquantization\(hynoise ratio
in dB, can be
evaluated for any specified type of PCM system as a function of input speech
level. It has been found that the subjective effect of a given value of
\fIQ\fR can be approximated by that of a level of continuous circuit noise
\fIG\fR \ dB below the speech level, where
\v'6p'
.RT
.sp 1P
.ce 1000
\fIG\fR \ =\ 1.07\ +\ 0.285\ \fIQ\fR \ +\ 0.0602\ \fIQ\fR \u2\d.
.ce 0
.sp 1P
.PP
.sp 1
Thus for a connection involving PCM links, one must include an
evaluation of equivalent noise level in the iterative process that determines
\fIV\fR\d\fIC\fR\u: each successive approximation to \fIV\fR\d\fIC\fR\uleads
to a new value
for \fIQ\fR , hence to a new value for \fIG\fR , and hence to a new contribution
to the circuit noise to be taken into account in calculating the new value
of
\fIY\fR\d\fIL\fR\\d\fIE\fR\u. In practice these modifications have negligible
effect
unless the speech level at the input to the PCM system falls below about
\(em25\ dBV, or the circuit noise at the same point is very high, or the speech
input level is so high (say > | (em5\ dBV) that appreciable peak limiting
occurs.
.sp 1P
.LP
2.10.2
    \fISyllabic companding\fR
.sp 9p
.RT
.PP
The case of a 2:1 syllabic compandor can be simply handled by
finding a subjectively equivalent continuous noise level.
.PP
Let \fIS\fR  | be the speech level at the input to the compressor, and
\fIN\fR  | be the noise level (psophometrically weighted) arising between
the compressor and expander, both in dB relative to unaffected level. The
resultant levels at the output of the expander will then be as given in
Table\ 2\(hy2.
.RT
.LP
.sp 1
.ce
\fBH.T. [T3.3]\fR
.ce
TABLE\ 2\(hy2
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(120p) | cw(24p) | cw(42p) | cw(42p) .
    Speech    Noise while  speech present    Noise while  speech absent
_
.T&
lw(120p) | cw(24p) | cw(42p) | cw(42p) .
Level at compressor input    S    \(em    \(em
.T&
lw(120p) | cw(24p) | cw(42p) | cw(42p) .
Gain of compressor (dB)    \(emS/2    \(em    \(em
.T&
lw(120p) | cw(24p) | cw(42p) | cw(42p) .
 {
Level at compressor output and expander input
 }    \ S/2    N    N
.T&
lw(120p) | cw(24p) | cw(42p) | cw(42p) .
Gain of expander (dB)    \ S/2    S/2    N
.T&
lw(120p) | cw(24p) | cw(42p) | cw(42p) .
Level at expander output    S    N |  | /2    2N
.T&
lw(120p) | cw(24p) | cw(42p) | cw(42p) .
 {
Level at same point in absence of compander
 }    S    N    N
.T&
lw(120p) | cw(24p) | cw(42p) | cw(42p) .
Improvement    \(em    \(emS/2    \(emN
_
.TE
.nr PS 9
.RT
.ad r
\fBTable 2\(hy2 [T3.3], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 1
.PP
Note that \fIS\fR  | and \fIN\fR  | are both normally negative, so that the
improvements are positive. Any noise present at the compressor input will be
present at the same level at the expander output, and will combine by power
addition with the other noise at the same point.
.bp
.PP
Subjectively equivalent performance is obtained by omitting the
compandor and substituting a continuous noise level satisfying the
condition:
.RT
.LP
    Total\ improvement
    =
    \ 1/3 (improvement in presence of speech) +
.LP
+2/3 (improvement in absence of speech)
.LP
    =
    \(em\fIS\fR /6 \(em 2\fIN\fR /3.
.LP
Hence
.LP
    equivalent\ noise\ level
    =
    \fIN\fR \(em improvement
.LP
    =
    \fIN\fR \ +\ \fIS\fR /6\ +\ 2\fIN\fR /3\ =\ \fIS\fR /6 +\ 5\fIN\fR /3.
.PP
This noise level is recalculated from \fIV\fR\d\fIC\fR\u | on each iteration
and used to calculate the next value of \fIY\fR\d\fIL\fR\\d\fIE\fR\u.
.sp 1P
.LP
2.10.3
    \fIDelay and echo\fR
.sp 9p
.RT
.PP
The audibility and objectionability of echo can be expressed
as a reasonably simple function of the delay and loudness rating of the
echo path, but the wider effects of echo and main\(hypath delay in disrupting
conversation can at present only be treated by \fIad hoc\fR estimation from the
known performance of circuit conditions in neighbouring parts of the range.
Steps are being taken to extend the model in this direction, account being
taken also of the interaction of delay and echo with sidetone and nonlinear
distortions.
.RT
.sp 1P
.LP
2.10.4
    \fICrosstalk\fR
.sp 9p
.RT
.PP
The loudness part of the model may be used to estimate the
audibility of crosstalk, at various attenuations, and hence to find the
attenuation required to reduce it to an inaudible level or to an acceptable
level.
.RT
.sp 1P
.LP
2.11
    \fIPractical use of the model\fR
.sp 9p
.RT
.PP
At the academic or research level, the chief use of a model of this kind
is in promoting an understanding of the fundamentals of telecommunication
between human beings, and in finding potential improvements in the techniques
of telecommunication systems.
.PP
At the practical level, the chief advantage of having the model
available is that it encodes the knowledge of the performance of telephone
connections in a very economical manner, obviating the need for large and
complex tabulations or graphs. For connections containing only the \*Qnatural\*U
degradations, the program CATNAP greatly facilitates routine use of the
model. The user of this program need not know anything about the theory
beyond the
meaning of the terms and symbols used, and need not normally make any special
measurements. Connections are specified in terms of standard items and
quantities, such as noise levels, telephones of particular types, lengths of
cable with stated resistance and capacitance per kilometre, and attenuators
with stated loss. Starting from these data, the program performs all the
necessary calculations and prints out loudness ratings, speech levels, and
opinion scores (\fIY\fR\d\fIL\fR\\d\fIE\fR\uand \fIY\fR\d\fIC\fR\u). More
detail can be printed on request.
.PP
It would of course be possible to construct a large table of results covering
a wide range of connections, but the table would have to be either too
large to be practical or else limited by making arbitrary fixed choices
for
many of the variables. In either case the advantage of having the model
\(em that it holds the information in an economically coded form and releases
only the
required part on demand \(em would be lost.
.PP
CATNAP may also be used inversely. Suppose it is desired to find what value
of some variable in a connection (the independent variable) will yield
a given value of one of the dependent variables. By performing runs at
different values of the independent variable one identifies a region within
which the
required value lies; one can then repeat the calculation at ever smaller
intervals until the required value is located with sufficient accuracy. For
example, where all features except the local line remain fixed, one can find
the line length (for the type of cable in question) that will yield values
of OLR below some specified maximum, or values of \fIY\fR\d\fIC\fR\uabove
some specified
minimum. More than one independent variable could of course be adjusted, but
correspondingly more work would then be needed in order to find the
combinations that satisfied the criterion.
.PP
The usefulness of these facilities is evident.
.bp
.RT
.sp 2P
.LP
\fB3\fR \fBCalculation of transmission performance from objective measurements
by the information index method\fR (Contribution by France)
.sp 1P
.RT
.sp 1P
.LP
3.1
    \fIIntroduction; type of model\fR
.sp 9p
.RT
.PP
The information index theory is given in [31]. This quantity can be calculated
from the results of objective measurements and some fundamental data on
speech and hearing. Among the factors listed in Question\ 7/XII\ [32] the
theory takes into account transmission loss, circuit noise, room noise,
attenuation/frequency distortion, sidetone and various distortions occuring
in digital transmission (Question\ 18/XII). The effect of other types of
nonlinear distortion is under study.
.PP
The model used here belongs to the second type mentioned in [33] and in
\(sc\ 2.1 of this Supplement, since it reflects de cause\(hyand\(hyeffect
relationships between the input (properties of the connection considered,
acoustic environment, loudness properties of speech and hearing) and the
output (mutual information transmitted between speaker and listener). This
Section
only describes the practical method for performing the computation of the
information index. As shown in\ [31] and also in Tables\ 3\(hy4 and\ 3\(hy7
below, the values thus computed are strongly correlated with the results
of subjective
opinion tests carried out in several countries.
.RT
.sp 2P
.LP
3.2
    \fIApplication to digital transmission\fR
.sp 1P
.RT
.sp 1P
.LP
3.2.1
    \fIDefinitions\fR
.sp 9p
.RT
.PP
Table 3\(hy1 defines the various signal\(hyto\(hynoise ratios to be
considered (in\ dB).
.RT
.ce
\fBH.T. [T4.3]\fR
.ce
TABLE\ 3\(hy1
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(30p) sw(30p) | cw(120p) , c | c | ^ .
Notations    Definitions
See Note 1    See Note 2
_
.T&
cw(30p) | cw(30p) | lw(120p) .
\fIQ\fI    \fIQ\fR , \fIQ\fI     {
Signal\(hyto\(hynoise ratio, kept constant by a MNRU
 }
.T&
cw(30p) | cw(30p) | lw(120p) .
\fIQ\fI    \fIQ\fI     {
Segmental signal\(hyto\(hynoise or signal\(hyto\(hydistortion ratio (in dB) (mean of ratios computed over segments of 16 or 32 ms)
 }
.T&
cw(30p) | cw(30p) | lw(120p) .
\fIQ\fI         {
Ratio (in dB) of the mean signal power to mean noise or distortion power, for speech\(hycorrelated noise
 }
.TE
.LP
\fINote 1\fR
\ \(em\ Over the transmitted band.
.LP
\fINote 2\fR
\ \(em\ At frequency \fIf\fI .
.nr PS 9
.RT
.ad r
\fBTable 3\(hy1 [T4.3], p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
Let \fIs\fR  | be the original speech signal and \fIr\fR  | the reconstructed
signal, we have:
\v'6p'
.ce 1000
\fIQ\fR\d\fIP\fR\u= 10 log\d1\\d0\u
@ left [   int  fIs\fR~\u2\d~/  int  \fIs\fR~\(em~\fIr\fR )\u2\d right ] @  dB
.ce 0
.ad r
(3\(hy1)
\v'7p'
.ad b
.RT
.PP
.sp 1
If the sums are taken over an entire speech utterance, \fIQ\fR\d\fIp\fR\u |
is not a satisfactory quality criterion; for a sampling frequency of 8\
kHz, we
have:
\v'6p'
.ce 1000
\fIQ
\dseg
\u\fR =
[Unable to Convert Formula]
@ pile { fIM\fR~\(em1 above sum above \fIm\fR~=0 } @
10 log\d1\\d0\u$$3o
@ pile { 28 above sum above \fIj\fR~=1 } @
\fIs\fR \u2\d (
\fIj\fR + 128 \fIm\fR )
$$3u
@ pile { 28 above sum above \fIj\fR~=1 } @
[\fIs\fR (
\fIj\fR + 128 \fIm\fR ) \(em
\fIr\fR (
\fIj\fR + 128 \fIm\fR )]\u2\d
$$3e dB
.ce 0
.ad r
(3\(hy2)
\v'1P'
\v'11p'
.ad b
.RT
.LP
.sp 1
where \fIM\fR  | is the number of 16 ms segments.
.bp
.PP
To determine \fIQ\fR\d\fIs\fR\u, the spectra of the signal, \fIs\fR  |
and of the distortion (\fIs\fR \ \(em\ \fIr\fR ) are computed over 256\
samples of 32\ ms duration and divided into the appropriate frequency bands.
Then the segmental
signal\(hyto\(hydistortion ratio is computed in each band.
.sp 1P
.LP
3.2.2
    \fIBasic formulas\fR
.sp 9p
.RT
.PP
The
information index
\fII\fR\d\fII\fR\u | (in dB), defined in [31],
is given by
\v'6p'
.RT
.ce 1000
\fII\fR\d\fII\fR\u=
@ pile { sum above \fIj\fR } @ \fIB\fR\d\fIj\fR\u\(mu \fIV\fR\d\fIj\fR\u
.ce 0
.ad r
(3\(hy3)
\v'8p'
.ad b
.RT
.LP
.sp 1
with
\v'6p'
.ce 1000
\fIV\fR\d\fIj\fR\u=
[Unable to Convert Formula]
.ce 0
.ad r
(3\(hy4)
\v'7p'
.ad b
.RT
.LP
.sp 1
.PP
\fIB\fR\d\fIj\fR\u | is the weight allocated to the band of rank\ \fIj\fR ;
\fIC\fR\d\fIj\fR\u\ =\ 10 log\d1\\d0\u(
\fIf\fR\d\fIj\fR\u/\(*D\fIf\fR\d\fIc\fR\u),
\(*D\fIf\fR\d\fIc\fR\u | being the
critical bandwidth
.
.PP
Table 3\(hy2 gives the values of \fIB\fR\d\fIj\fR\u | and \fIC\fR\d\fIj\fR\u |
for the bands
which are used in the example of \(sc\ 3.2.4; they are reproduced in lines\ 70
and\ 80 of Appendix\ I. Values for ISO preferred frequencies (3rd\ octave
spaced) from 0.1 to 8\ kHz are given in lines\ 180\(hy370 of Appendix\
II under columns\ BJ
and\ CJ.
.RT
.LP
.sp 4
.ce
\fBH.T. [T5.3]\fR
.ce
TABLE\ 3\(hy2
.ce
\fBFrequency weighting\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(24p) | cw(84p) | cw(42p) | cw(42p) .
\fIj\fR     {
Equal articulation bands
Extreme frequencies (Hz)
 }    \fIB\fI  \(mu 10\u5\d    \fIC\fI  (dB)
_
.T&
cw(24p) | cw(42p) | cw(42p) | cw(42p) | cw(42p) .
\ 1    \  | 00    \  | 30    \ \ 5 | 57    4.1
.T&
cw(24p) | cw(42p) | cw(42p) | cw(42p) | cw(42p) .
\ 2    \  | 30    \  | 30    \ \ 4 | 33    5.6
.T&
cw(24p) | cw(42p) | cw(42p) | cw(42p) | cw(42p) .
\ 3    \  | 30    \  | 60    \ \ 6 | 82    6.4
.T&
cw(24p) | cw(42p) | cw(42p) | cw(42p) | cw(42p) .
\ 4    \  | 60    \  | 00    \ \ 7 | 97    6.9
.T&
cw(24p) | cw(42p) | cw(42p) | cw(42p) | cw(42p) .
\ 5    \  | 00    \  | 40    \ \ 6 | 46    7.4
.T&
cw(24p) | cw(42p) | cw(42p) | cw(42p) | cw(42p) .
\ 6    \  | 40    1 | 00    \ \ 6 | 22    7.8
.T&
cw(24p) | cw(42p) | cw(42p) | cw(42p) | cw(42p) .
\ 7    1 | 00    1 | 50    \ \ 5 | 85    8.0
.T&
cw(24p) | cw(42p) | cw(42p) | cw(42p) | cw(42p) .
\ 8    1 | 50    1 | 10    \ \ 5 | 00    8.0
.T&
cw(24p) | cw(42p) | cw(42p) | cw(42p) | cw(42p) .
\ 9    1 | 10    1 | 80    \ \ 5 | 73    8.2
.T&
cw(24p) | cw(42p) | cw(42p) | cw(42p) | cw(42p) .
10    1 | 80    1 | 60    \ \ 5 | 17    8.2
.T&
cw(24p) | cw(42p) | cw(42p) | cw(42p) | cw(42p) .
11    1 | 60    1 | 30    \ \ 4 | 17    8.2
.T&
cw(24p) | cw(42p) | cw(42p) | cw(42p) | cw(42p) .
12    1 | 30    2 | 20    \ \ 4 | 06    8.2
.T&
cw(24p) | cw(42p) | cw(42p) | cw(42p) | cw(42p) .
13    2 | 20    2 | 40    \ \ 5 | 73    8.2
.T&
cw(24p) | cw(42p) | cw(42p) | cw(42p) | cw(42p) .
14    2 | 40    2 | 00    \ \ 5 | 61    8.2
.T&
cw(24p) | cw(42p) | cw(42p) | cw(42p) | cw(42p) .
15    2 | 00    2 | 20    \ \ 6 | 10    8.2
.T&
cw(24p) | cw(42p) | cw(42p) | cw(42p) | cw(42p) .
16    2 | 20    3 | 00    \ \ 6 | 86    8.1
_
.T&
lw(24p) | cw(84p) | cw(42p) | lw(42p) .
    TOTAL    102 | 58
_
.TE
.nr PS 9
.RT
.ad r
\fBTable 3\(hy2 [T5.3], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
3.2.3
     \fIRelations between signal\(hyto\(hynoise ratios in the case of digital\fR
\fItransmission\fR
.sp 9p
.RT
.PP
In the case of MNRUs with uniform or shaped noise, from the very
principle of their operation, \fIQ\fR\d\fIs\fR\u\ =\ \fIQ\fR\d\fIj\fR\uand
Equation\ (3\(hy4) may be
applied directly if \fIQ\fR\d\fIs\fR\uin each band is known.
.PP
For digital coders, the equivalence law in lines 150\(hy170 of
Appendix\ I is used. The law depends on two parameters, \fIK\fR\d1\uand
\fId\fR \ =\ \fIQ\fR\d\fIs\fR\\d\fIe\fR\\d\fIg\fR\u\ \(em\ \fIQ\fR\d\fIp\fR\u.
Numerical computations have shown that this law is valid both for PCM (\fIK\fR\d1\u\
=\ 5.2; \fId\fR \ =\ 0) and for natural speech (\fIK\fR\d1\u\ =\ 5.2; \fId\fR
\ =\ \(em5.3)\ [31]. The example of \(sc\ 3.2.4 shows that it gives
consistent results for various types of coders.
.RT
.sp 1P
.LP
3.2.4
    \fIProgram and example of application\fR
.sp 9p
.RT
.PP
The program used is reproduced in Appendix I.
.PP
Table 3\(hy3 gives measured values of the signal\(hyto\(hynoise ratios
defined above for MNRUs and for a variety of codecs, as well as the information
index values computed from these results as the mean opinion scores (MOS)
for
listening determined in the CNET Laboratory\ [34].
.PP
Table 3\(hy4 shows the correlation of these MOS with the information
index (Table 3\(hy3) and with other objective measures of transmission
performance which have been proposed.
.RT
.sp 2P
.LP
3.3
    \fIApplication to analogue transmission\fR
.sp 1P
.RT
.sp 1P
.LP
3.3.1
    \fIGeneral; use of the program\fR
.sp 9p
.RT
.PP
The calculation of the information index, in the case of analogue transmission,
will be explained with reference to the program reproduced as
Appendix\ II. This applies to a connection composed of two telephone sets
of the NTT\ 600 type (with 7\ dB subscriber lines), one SRAEN filter and
a variable
attenuation. Writing the corresponding program for other types of connection
is discussed in \(sc\ 3.4.
.PP
The program is used in the following way:
.RT
.LP
    a)
    enter RN, STMR, ICN\d0\u | as defined in lines 30\(hy60,
press\ \*QL\*U, enter OLR; read IN = information index
(listening);
.LP
    b)
    if \fII\fR\d\fIc\fR\u |
.FS
See Table 3\(hy5.
.FE
(information index under conversation conditions) is
required, press\ \*QC\*U; read IN = \fII\fR\d\fIc\fR\u;
.LP
    c)
    press \*QT\*U.
.sp 1P
.LP
3.3.2
    \fIData\fR
.sp 9p
.RT
.PP
Lines 170\(hy370 of the program.
.PP
Lines 180\(hy370 correspond to 1/3 octave spaced frequencies from 0.1 to
8\ kHz.
.RT
.sp 1P
.LP
3.3.2.1
    \fIBasic data\fR
.sp 9p
.RT
.PP
These do not depend on the type of telephone set used.
.RT
.LP
    BK
    =
    Hearing threshold for continuous\(hyspectrum sounds
(\fIL\fR\d\fIs\fR\uin\ [31]) referred to ear reference point;
.LP
    S
    =
    Spectrum density (long\(hyterm mean intensity) of speech
at the mouth reference point; S\ +\ 0.4\ dB corresponds
to a vocal level \(em4.7\ dB/1\ Pa;
.LP
    BJ
    =
    frequency weighting (see [31]);
.LP
    CJ
    =
    correction term in formula 3.4 giving \fIV\fR\d\fIj\fR\u.
.sp 1P
.LP
3.3.2.2
    \fIElectroacoustic characteristics\fR
.sp 9p
.RT
.PP
These depend on the connection considered.
.RT
.LP
    SRL
    =
    Loss (send + receive) of the local system;
.LP
    D1
    =
    Loss of the line filter.
.bp
.ce
\fBH.T. [T6.3]\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
[Unable to Convert Table]
.LP
MNRUS
=\ MNRU with shaped noise
.LP
F
=\ ADPCM with fixed predictor
.LP
V
=\ ADPCM with variable predictor
.LP
SB
=\ Sub\(hyband coding
.nr PS 9
.RT
.ad r
\fBTable 3\(hy3 [T6.3],\ \
A L'ITALIENNE, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.ce
\fBH.T. [T7.3]\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(342p) .
TABLE\ 3\(hy4
.T&
cw(342p) .
 {
\fBCorrelation between MOS and various objective measures of transmission
performance in the case of digital transmission\fR
 }
.TE
.TS
center box ;
cw(72p) | cw(30p) sw(24p) sw(30p) sw(24p) sw(30p) sw(24p) sw(30p) sw(24p) sw(30p) sw(24p) , ^  | c s | c | c s | c | c s
^  | c | c | c | c | c | c | c | c | c | c.
Objective measure  (Note)    Systems
    Group B  PCM, ADM, ADPCM\(hyF     {
Group A
same as B + ATC
APC \(em AB
 }     {
Group F
ADPCM\(hyF, ADPCM\(hyV
 }     {
Group E
same as F + sub\(hyband
coding
 }     {
Group D
same as E + MNRU
shaped MNRU
 }    R    S    R    S    R    S    R    S    R    S
_
.T&
lw(72p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | lw(24p) .
\fIQ\fI  (SNR)    0.798    0.578    0.803    0.559    0.687    0.680    0.590    0.711    0.650
.T&
lw(72p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | lw(24p) .
\fIQ\fI  (SNR seg)    0.950    0.301    0.894    0.430    0.906    0.396    0.725    0.606    0.720
.T&
lw(72p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | lw(24p) .
\*QLog likelihood ratio\*U    0.943    0.213    0.924    0.341
.T&
lw(72p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | lw(24p) .
Cepstrale distance    0.954    0.208    0.929    0.331
.T&
lw(72p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | lw(24p) .
SRNF                                    0.884
.T&
lw(72p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) .
Information index                    0.994    0.101    0.993    0.102    0.976    0.175
.TE
.LP
\fINote\fR
\ \(em\ Notations from Table 3\(hy1; see also Contribution COM
XII\(hyNo. 8 (Study Period 1985\(hy1988).
.LP
SNRF
=\ \fIQ\fI
 | frequency weighted
.LP
R
=\ Correlation coefficient
.LP
S
=\ Standard deviation (in terms of MOS on a 0 to 4 or 1 to 5 scale)
.nr PS 9
.RT
.ad r
\fBTable 3\(hy4 [T7.3]\ \
A L'ITALIENNE, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
3.3.2.3
    \fINoise components\fR
.sp 9p
.RT
.PP
The following components (which depend on the connection) are
considered.
.RT
.LP
    BDFE
    =
    spectrum of far\(hyend room noise via far\(hyend
telephone set;
.LP
    BDCN
    =
    spectrum of circuit noise;
.LP
    BDST
    =
    spectrum of near\(hyend room noise via sidetone
path;
.LP
    BDEL
    =
    spectrum of near\(hyend room noise via earcap
leakage.
.PP
The data at lines 180\(hy370 correspond to a typical connection. They are:
.LP
    FE
    =
    BDFE computed for RN\ =\ 50\ dBA and an overall loudness
rating (OLR), according to Recommendation\ P.79, of
5\ dB;
.LP
    CN
    =
    BDCN computed for ICN\d0\u\ =\ \(em60\ dBmp;
.LP
    ST
    =
    BDST computes for RN\ =\ 50\ dBA and STMR = 15\ dB;
.LP
    EL
    =
    BDEL computed for RN\ =\ 50\ dBA.
.PP
The computations were made [35] from the frequency characteristics given
in\ [36], by a method similar to that used for deriving Table\ 3 from
Table\ 2 in\ [33].
.sp 2P
.LP
3.3.3
    \fIComputation of signal\(hyto\(hynoise ratios\fR
.sp 1P
.RT
.sp 1P
.LP
3.3.3.1
    \fILevel of the signal\fR
.sp 9p
.RT
.PP
First, OLR is corrected if it is smaller than the optimum value
(see Appendix\ II, lines\ 100\(hy160). This optimum is determined by a
subroutine
(lines\ 720\(hy810) which is similar to the formulas of\ [38], but was
adapted to
the results of subjective opinion tests published in\ [36].
.RT
.sp 1P
.LP
3.3.3.2
    \fISignal\(hyto\(hynoise ratio\fR  | (lines 425\(hy440)
.sp 9p
.RT
.PP
The power sum of the noise components is taken and the
signal\(hyto\(hynoise ratio\ \fIZ\fR\d\fIn\fR\uthus obtained.
.RT
.sp 1P
.LP
3.3.3.3
    \fIEffect of thresholds\fR  | (lines 450\(hy480)
.sp 9p
.RT
.PP
\fIZ\fR\d\fIa\fR\u | is computed (see [31]) from which the equivalent
signal\(hyto\(hynoise ratio\ \fIZ\fR\d\fIe\fR\uis derived. The resultant\
\fIZ\fR is obtained by
power summation of the noises corresponding to \fIZ\fR\d\fIn\fR\uand\ \fIZ\fR\d\fIe\fR\u.
.RT
.sp 1P
.LP
3.3.4
    \fIInformation index for a constant speech level, I\fI\d\fIL\fR\u
.sp 9p
.RT
.PP
The equivalence between \fIZ\fR  | and \fIQ\fR  | is derived from the values
under \*QJapan\*U in Table\ 1 of [37], then \fIV\fR  | is computed at each
frequency
(lines\ 650\(hy700) and IN for listening is obtained (lines\ 500\(hy550).
.RT
.sp 1P
.LP
3.3.5
    \fIConversation information index\fR \fI, I\fI\d\fIc\fR\u
.sp 9p
.RT
.PP
First, speech power is modified to take into account the effect of sidetone
when talking (lines\ 90 and\ 560\(hy610), as in \(sc\ 2.7 above.
.PP
A second correction is added (line 620), as explained in [31]. The
application of the present model to 13\(hy2P\(hy27\(hytype telephone sets
with the
equivalence law mentioned under\ 3.3.4 gives:
\v'6p'
.RT
.sp 1P
.ce 1000
\fIV\fR\d\fIc\fR\u\(em \fIV\fR\d\fIL\fR\u= 9.87 \(em 0.4085 \fII\fR\d\fIL\fR\u
.ce 0
.sp 1P
.LP
.sp 1
.sp 1P
.LP
3.3.6
    \fIExamples\fR
.sp 9p
.RT
.PP
Table 3\(hy5 gives the MOS determined subjectively in two tests (one listening,
one under conversation conditions) for the same conditions, reported in\
[36], and the information indexes computed for these conditions.
.PP
Table 3\(hy6 gives the subjective MOS determined for various conditions
of noise and the corresponding listening information indexes.
.PP
Table 3\(hy7 shows the correlation between subjective MOS and the values
of information index given in Table\ 3\(hy5 and Table\ 3\(hy6, as well
as the results of similar calculations for 13\(hy2P\(hy27\(hytype telephone
sets.
.bp
.RT
.ce
\fBH.T. [T8.3]\fR
.ce
TABLE\ 3\(hy5
.ce
\fBInformation index I for NTT 600\(hytype telephone sets (7 dB line) with
.ce
SRAEN filter,\fR
.ce
\fBSTMR = 7.1 dB and opinion scores from tests
.ce
2 and 6\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) .
RN  (dBA)    CN  (dBmp)    ICN 0  (dBmp)    OLR  (dB)    \fIY\fI    \fII\fI  (dB)    \fIY\fI    \fII\fI  (dB)
_
.T&
cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) .
(1)    (2)    (3)    (4)    (5)    (6)    (7)    (8)
_
.T&
cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) .
60    \(em62.1    \(em58.2    \ 1.4    3.13    23.48    2.94    23.27
.T&
cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) .
            11.4    2.5\     22.75    2.34    22.50
.T&
cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) .
            21.4    2.31    19.44    1.58    19.52
.T&
cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) .
            31.4    0.65    12.28    0.2\     15.13
.T&
cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) .
60    \(em59.8    \(em55.9    \ 1.4    3.1\     23.52
.T&
cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) .
            11.4    2.91    22.73
.T&
cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) .
            21.4    1.75    19.35
.T&
cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) .
            31.4    0.8\     12.02
.T&
cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) .
60    \(em55.8    \(em51.9    \ 1.4    2.83    23.59    2.99    23.38
.T&
cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) .
            11.4    2.75    22.65    2.39    22.39
.T&
cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) .
            21.4    1.79    19.03    1.28    19.20
.T&
cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) .
            31.4    0.5\     11.24    0.43    14.71
.T&
cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) .
60    \(em51.4    \(em47.5    \ 1.4    3.06    23.66    3.08    23.43
.T&
cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) .
            11.4    2.24    22.44    2.17    22.16
.T&
cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) .
            21.4    1.05    18.27    1.29    18.64
.T&
cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) .
            31.4    0.09    \ 9.3\     0.22    14.11
.T&
cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) .
60    \(em45.6    \(em41.7    \ 1.4    2.31    23.64    2.63    23.37
.T&
cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) .
            11.4    1.4\     21.67    1.73    21.39
.T&
cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) .
            21.4    0.64    16.2\     0.77    17.23
.T&
cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) | cw(30p) | cw(24p) .
            31.4    0.05    \ 5.57    0.13    12.08
.TE
.LP
\fIExplanation of columns\fR
.LP
(1)
Room noise, dBA
.LP
(2)
Circuit noise at input to receiving end, dBmp
.LP
(3)
ICN
0 = CN + 3.9 dB
.LP
(4)
OLR (Rec. P.79)
.LP
(5)
Listening MOS (on a 0 to 4 scale), test 2 of
[36], p.\ 4\(hy4
.LP
Listening information index (position L of Appendix II)
.LP
Conversation MOS, test 6 of [36], p. 4\(hy9
.LP
Conversation opinion index (position C of
Appendix\ II)
.nr PS 9
.RT
.ad r
\fBTableau 3\(hy5 [T8.3], p. 32\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 8P
.ad r
Blanc
.ad b
.RT
.LP
.bp
.ce
\fBH.T. [T9.3]\fR
.ce
TABLE\ 3\(hy6
.ce
\fBInformation index at listening for NTT 600\(hytype telephone sets (7 dB
.ce
line) with SRAEN filter,\fR
.ce
\fBSTMR = 7.1 dB and listening
.ce
opinion score from test 4\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(36p) | cw(42p) | cw(42p) | cw(36p) | cw(36p) | cw(36p) .
RN  (dBA)    CN  (dBmp)    ICN 0  (dBmp)    OLR  (dB)    \fIY\fI    \fII\fI  (dB)
_
.T&
cw(36p) | cw(42p) | cw(42p) | cw(36p) | cw(36p) | cw(36p) .
\ 0    \fB.\fR (see Note)     {
\(em100\fB.\ \fR
(see Note)
 }     {
\(em3.6
\ 1.4
\ 6.4
\ 11.4
\ 16.4
\ 21.4
\ 26.4
\ 31.4
 }     {
2.30
2.83
3.26
2.92
2.59
2.12
1.89
1.23
 }     {
22.87
23.40
23.85
23.55
23.05
22.45
21.73
20.91
 }
_
.T&
cw(36p) | cw(42p) | cw(42p) | cw(36p) | cw(36p) | cw(36p) .
60    \(em55.8    \ \(em51.9     {
\(em3.6
\ 1.4
\ 6.4
\ 11.4
\ 16.4
\ 21.4
\ 26.4
\ 31.4
 }     {
2.61
2.94
3.00
2.38
1.80
1.41
0.91
0.44
 }     {
22.78
23.59
23.51
22.65
21.24
19.03
15.95
11.44
 }
_
.T&
cw(36p) | cw(42p) | cw(42p) | cw(36p) | cw(36p) | cw(36p) .
60    \(em56.9    \ \(em53\fB.9\fR    \ 1.4 \ 11.4 \ 21.4 \ 31.4    3.20 2.53 1.24 0.24    23.57 22.68 19.15 11.51
_
.T&
cw(36p) | cw(42p) | cw(42p) | cw(36p) | cw(36p) | cw(36p) .
50    \(em55.8    \ \(em51.9    \ 1.4 \ 11.4 \ 21.4 \ 31.4    3.21 2.64 1.58 0.35    23.88 23.24 21.04 15.94
_
.T&
cw(36p) | cw(42p) | cw(42p) | cw(36p) | cw(36p) | cw(36p) .
45    \(em64.9    \ \(em61\fB.9\fR    \ 1.4 \ 13.4    3.23 2.62     {
23.77
23.24
 }
.TE
.LP
\fINote\fR
\ \(em\ In these cases, there was no circuit noise during the opinion tests
but a noise corresponding to CN\ =\ \(em76.9 (ICN
0\ =\ \(em73) is used in the OPINE
model. An arbitrary low noise value may be used for the calculation of the
information index.
.nr PS 9
.RT
.ad r
\fBTableau 3\(hy6 [T9.3], p. 33\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 11P
.ad r
Blanc
.ad b
.RT
.LP
.bp
.ce
\fBH.T. [T10.3]\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(342p) .
TABLE\ 3\(hy7
.T&
cw(342p) .
 {
\fB\fBCorrelation between MOS and the information index in the case of
analogue transmission\fR
 }
.TE
.TS
center box ;
cw(90p) | cw(36p) sw(36p) sw(36p) | cw(36p) | cw(36p) | cw(36p) sw(36p) , ^  | c | c | c ^  | ^  | | c | c.
Type of connection     {
Range of conditions (see Note)
 }    Type of MOS    Correlation coefficient     {
Deviation in terms of \fIY\fR
 }
    RN  (dBA)    ICN 0  (dBmp)    OLR  (dB)    Standard error    Extreme deviations
_
.T&
lw(90p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) , ^  | c | c | c | c | c | c | c.
 {
NTT 600\(hytype telephone sets + SRAEN filter
 }    0 to 60     {
\(em\(if and
\(em61\fB.\ \fR
to \(em52\fB.\ \fR
 }    \(em3.6 to +31.4    Y L    0.978    0.15    \(em0.34 + 0.31
    60    \(em58.2 to \(em41.7    +1.4 to +31.4    Y C    0.977    0.16    \(em0.32 + 0.32
_
.T&
lw(90p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) , ^  | c | c | c | c | c | c | c.
 {
13\(hy2P\(hy27\(hytype telephone sets + attenuator
 }    50     {
\(em\(if and
\(em71\fB.\ \fR
to \(em49\fB.\ \fR
 }     {
\ +4\fB.6\fR
to +48\fB.4\fR
 }    Y C    0.995    0.07    \(em0.17 + 0.16
.TE
.LP
\fINote\fR
\ \(em\ Notations are of Appendix II.
.TE
.nr PS 9
.RT
.ad r
\fBTableau 3\(hy7 [T10.3], \ \ A L'ITALIENNE, p. 34\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 2P
.LP
3.4
    \fIPossible extensions\fR
.sp 1P
.RT
.sp 1P
.LP
3.4.1
    \fIFrequency characteristics\fR
.sp 9p
.RT
.PP
Appendix II gives an example which is explained in \(sc\ 3.3 above. If
different types of sets, balancing networks, subscriber's lines or line
filters are used, the corresponding data in Appendix\ II should be changed
accordingly and the noise data recalculated. This is the same procedure
as is given in the model of \(sc\ 2.4 above and is explained in\ [33].
.PP
OLR and STMR, used as independent variables, should be recalculated
according to Recommendation\ P.79.
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3.4.2
    \fIConnection including digital processes\fR
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.PP
Paragraph\ 3.2 above and Appendix\ I apply to cases where speech is near
its optimum level, in order to compare different coders under such
conditions. If the coders give rise to appreciable clipping, the loss of
information due to this effect should be calculated and the corresponding
value of\ \fIQ\fR determined as explained in\ [31].
.PP
Anyhow, when digital process are included in a connection of a
telephone network, the corresponding values of \fIQ\fR\d\fIm\fR\ushould
be determined in each frequency band and combined with the value of\ \fIQ\fR
in Appendix\ II, by a
power summation of the noises and distortions.
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