InfoMagic Standards 1993 July/Disc.iso/ccitt/1988/troff/5_1_05.tro

Text File | 1991-12-13 | 121.6 KB | 4,959 lines

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.rs
\v | 5i'
.sp 1P
.ce 1000
\v'3P'
SECTION\ 6
.ce 0
.sp 1P
.ce 1000
\fBMEASUREMENTS\ RELATED\ TO\ SPEECH\ LOUDNESS\fR \v'3P'
.ce 0
.sp 1P
.sp 2P
.LP
\fBRecommendation\ P.75\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBSTANDARD\ CONDITIONING\ METHOD\ FOR\ HANDSETS\fR  |
\fBWITH\ CARBON\ MICROPHONES\fR
.EF '%    Volume\ V\ \(em\ Rec.\ P.75''
.OF '''Volume\ V\ \(em\ Rec.\ P.75    %'
.ce 0
.sp 1P
.ce 1000
\fI(Geneva, 1972; amended at Malaga\(hyTorremolinos, 1984, Melbourne, 1988)\fR
\v'1P'
.sp 9p
.RT
.ce 0
.sp 1P
.PP
\fB1\fR
Since the characteristics of carbon
microphones are strongly dependent on conditioning techniques, it is
necessary to follow a consistent procedure prior to measuring
sensitivity/frequency characteristics in order to obtain reproducible results.
The CCITT recommends that for best reproducibility, automatic mechanical
conditioning be used. The following steps are specified for the \fIstandard\fR
\fIconditioning method\fR :
.sp 1P
.RT
.LP
    a)
    Place the handset in a holding fixture with the handset
clamped in a position corresponding to that in which the
microphone is going to be measured [e.g.\ loudness rating
guard\(hyring position (LRGP) according to Annex\ A of
Recommendation\ P.76].
.LP
    b)
    Connect the microphone or telephone set terminals as
required to the d.c. feed circuit and appropriate terminating
loading.
.LP
    c)
    Turn the feed current on. After 5\ seconds, condition the
microphone by rotating it smoothly. Rotation is made such that
the plane of the granule bed moves through an arc of at
least\ 180\(de. The procedure is repeated twice with the handset
coming to rest finally in the test position. The time of each
rotation cycle should lie within the range of 2\ to
12\ seconds.
.PP
\fB2\fR When carrying out subjective tests with a carbon microphone
telephone set, the conditioning of the handset should be done by the talker.
This conditioning should conform to the conditioning for objective measuring
as described under \(sc\ 1 above insofar as it is practicable.
.sp 9p
.RT
.LP
.rs
.sp 2P
.ad r
Blanc
.ad b
.RT
.LP
.bp
.sp 2P
.LP
\fBRecommendation\ P.76\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBDETERMINATION\ OF\ LOUDNESS\ RATINGS;\ FUNDAMENTAL\ PRINCIPLES\fR
.EF '%    Volume\ V\ \(em\ Rec.\ P.76''
.OF '''Volume\ V\ \(em\ Rec.\ P.76    %'
.ce 0
.sp 1P
.ce 1000
\fI(Geneva, 1976; amended at Geneva, 1980\fR
.sp 9p
.RT
.ce 0
.sp 1P
.ce 1000
\fIMalaga\(hyTorremolinos, 1984, Melbourne, 1988)\fR
.ce 0
.sp 1P
.LP
    \fBPreface\fR
.sp 1P
.RT
.PP
This Recommendation is one of a set of closely related
Recommendations concerned with determination of loudness ratings. The present
one deals with the fundamental principles and the others, as follows, deal
with certain additional matters
.FS
The present Recommendation together with
Recommendations\ P.48, P.78 and\ P.79 provide complete definitions of overall,
sending, receiving and junction loudness ratings, and Administrations are
invited to use them to further their studies of
Question\ 19/XII\ [1].
.FE
.
.RT
.LP
    Recommendation\ P.48
    Specification for an intermediate reference
system
.LP
    Recommendation\ P.78
    Subjective testing method for determination
of loudness ratings in accordance with
Recommendation\ P.76
.LP
    Recommendation\ P.64
    Determination of sensitivity/frequency
characteristics of local telephone systems to
permit calculation of their loudness ratings
.LP
    Recommendation\ P.79
    Calculation of loudness ratings
.LP
    Recommendation\ P.65
    Objective instrumentation for the
determination of loudness ratings
.sp 2P
.LP
\fB1\fR     \fBIntroduction\fR
.sp 1P
.RT
.PP
A
speech path
is, broadly, a transmission path that exists between a talker's mouth and
the ear of a listener or, in the case of sidetone, between the mouth and
ear of a talker. In typical face\(hyto\(hyface conversation,
the speech is transmitted by means of the air path connecting the mouth and
ear.  Depending on environmental conditions, transmission may be:
.RT
.LP
    a)
     more or less direct, as in the case of two persons conversing in an open,
unobstructed location, such as a golf course;
.LP
    b)
     largely indirect, as in the case of two persons conversing in a small,
hard surfaced room where a large proportion of the
energy reaching the ear may be due to reflections from the
walls, ceilings and floor; or
.LP
    c)
    something between the two extremes of\ \fIa)\fR and\ \fIb)\fR .
.PP
In the case of telephony, the air path is replaced by a system
comprising:
.LP
    a)
    an air path from the mouth to the telephone microphone;
.LP
    b)
    an air path between the telephone earphone and the ear; and
.LP
    c)
     a telephone connection consisting of the microphone, earphone and interconnecting
circuitry together with a similar system
for the reverse direction of transmission. The two
situations\ \(em face\(hyto\(hyface and using the telephone\ \(em differ
appreciably in detail but, for speech transmission purposes,
they are alike insofar as their function is to provide a
means of both\(hyway speech communication.
.PP
Telephone engineering is concerned with providing telephone
connections which, while not identical to the face\(hyto\(hyface situation, are
comparable in effectiveness for providing a means of exchanging information
by speech; such telephone connections should also optimize customer satisfaction
within technical and economic constraints.
.bp
.PP
Various tools are used by transmission engineers in planning, design
and assessment of the performance of telephone networks. Reference equivalent,
based on the criterion of loudness of speech emitted by the talker and
perceived by the listener, has been one of the most important of these
tools; it provides a measure of the transmission loss, from mouth to ear,
of a speech path.
.PP
The \fIreference equivalent method\fR  | s defined in Recommendations\
P.42 and\ P.72 \fIRed Book\fR and its fundamental principles are briefly
explained
in\ [2]. The method for determining \fIloudness ratings\fR of local telephone
circuits is based upon rather similar fundamental principles but comprises
modifications which render it much more flexible and should greatly simplify
transmission planning.
.PP
A desire to depart from use of reference equivalents as defined by
Recommendation\ P.72 \fIRed Book\fR  | arises from the following
reasons:
.RT
.LP
    1)
    reference equivalents cannot be added algebraically;
discrepancies of at least \(+- | \ dB are found;
.LP
    2)
    replication accuracy of reference equivalents is not good;
changes in crew can cause changes of as much as 5\ dB;
.LP
    3)
     increments of real (distortionless) transmission loss are not reflected
by equal increments of reference equivalent;
10\ dB increase in loss results in an increase in reference
equivalent of only about 8\ dB.
.PP
Use of loudness ratings defined in accordance with the principles given
below should largely obviate these difficulties.
.PP
In addition to these advantages, the same values of loudness ratings should
be obtained whether the determination is by subjective tests, by
calculation based on sensitivity/frequency characteristics or by objective
instrumentation. The fundamental principles of the method are described
below and these differ from those applicable to reference equivalents by
the least
possible extent to achieve the desirable flexibility.
.PP
The loudness rating (which has the dimensions and sign of \*Qloss\*U) is,
in principle, like the reference equivalent, defined by the amount of loss
inserted in a reference system to secure equality of perceived loudness
to that obtained over the speech path being measured. Practical telephone
connections are composed of several parts connected together. To enable the
transmission engineer to deal with these parts in different combinations,
loudness ratings must be defined in a suitable manner so that \*Qoverall\*U,
\*Qsending\*U, \*Qreceiving\*U and \*Qjunction\*U ratings can be used.
.PP
\*QSidetone\*U loudness ratings can also be determined in an analogous
manner. Sidetone reference equivalent is defined in Recommendation\ P.73
\fIRed Book\fR and sidetone loudness ratings are defined in
\(sc\ 3\ below.
.RT
.sp 2P
.LP
\fB2\fR     \fBDefinitions of\fR
\fBloudness ratings\fR \fBfor principal speech\fR \fBpaths\fR
.sp 1P
.RT
.sp 1P
.LP
2.1
    \fIGeneral\fR
.sp 9p
.RT
.PP
\(sc\ 2 deals with principal speech paths, namely from a
talker at one end of a connection to a listener at the other. Sidetone paths
are treated in \(sc\ 3\ below.
.PP
In general, loudness ratings are not expressed directly in terms of
actual perceived loudness but are expressed in terms of the amounts of
transmission loss, independent of frequency, that must be introduced into an
\fIintermediate\fR reference speech path and the \fIunknown\fR speech path to
secure the same loudness of received speech as that defined by a fixed
setting of NOSFER. This implies that some interface exists or could, by
some
arrangement, be found in the unknown speech path into which the transmission
loss can be introduced. In practice the unknown speech path is composed of a
.PP
sending local telephone circuit coupled to a receiving local telephone
circuit through a chain of circuits interconnecting the two local systems
.FS
See
Annex\ B for explanation of certain terms.
.FE
. Figure\ 1/P.76 shows this
subdivision of one principal speech path of a telephone connection. The
interfaces\ JS and\ JR separate the three parts of the connection to which
loudness ratings are assigned, namely:
\fIsending loudness rating\fR , from  the mouth reference point to\ JS;
\fIreceiving loudness rating\fR from\ JR to the ear reference point; and
\fIjunction loudness rating\fR from\ JS to\ JR.  The
\fIoverall loudness rating\fR is assigned to the whole speech path from
mouth reference point to ear reference point.
.bp
.RT
.LP
.rs
.sp 26P
.ad r
\fBFigure 1/P.76, p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
Note that in practical telephone connections:
.LP
    a)
    the transmission loss of the junction may be frequency
dependent;
.LP
    b)
     the image impedances of the \*Qjunction\*U may not be constant with frequency
and may not be resistive;
.LP
    c)
     the impedances of the local telephone systems presented to the junction
at\ JS and\ JR may not be constant with frequency and
may not be resistive;
.LP
    d)
    impedance mismatches may be present at\ JS or\ JR or
both.
.PP
Overall loudness ratings (OLRs), sending loudness ratings
(SLRs), receiving loudness ratings (RLRs) and junction loudness ratings
(JLRs) are defined so that the following equality is achieved with sufficient
accuracy for practical telephone connections.
\v'6p'
.sp 1P
.ce 1000
OLR\ =\ SLR\ +\ RLR\ +\ JLR
.ce 0
.sp 1P
.LP
.sp 1
.sp 1P
.LP
2.2
    \fIDefinitions of overall, sending, receiving and junction\fR
\fIloudness ratings\fR
.sp 9p
.RT
.PP
Figure 2/P.76 shows the principles used to define the overall,
sending, receiving and junction loudness ratings.
.RT
.sp 1P
.LP
2.2.1
    \fIOverall loudness rating\fR
.sp 9p
.RT
.PP
Path 1 in Figure 2/P.76 shows the complete unknown speech path
subdivided into local telephone systems and junction. In this example the
junction comprises a chain of circuits represented by trunk junctions (JS\(hyNS
and NR\(hyJR) and trunk circuits (NS\(hyIS, IS\(hyIR and IR\(hyNR). A suitable
arrangement for inserting transmission loss independent of frequency must
be provided at
some point such as in IS\(hyIR.
.bp
.RT
.LP
.rs
.sp 39P
.ad r
\fBFigure 2/P.76, p. 2\fR
.sp 1P
.RT
.ad b
.RT
.PP
Path 2 shows the complete intermediate reference system (IRS)
with its adjustable, non\(hyreactive, 600\ ohms junction between JS and\ JR.
.PP
The level of received speech sounds to which the additional
loss\ \fIx\fR\d1\uin Path\ 1 and the junction attenuator setting\ \fIx\fR\d2\uof
Path\ 2 are both adjusted is defined by using the fundamental reference
system NOSFER with its attenuator set at 25\ dB. When these adjustments have
been made, the overall loudness rating (OLR) of the complete unknown connection
is given by (\fIx\fR\d2\u\ \(em\ \fIx\fR\d1\u)\ dB.
.RT
.sp 1P
.LP
2.2.2
    \fISending loudness rating\fR
.sp 9p
.RT
.PP
Path 3 in Figure 2/P.76 shows the IRS with its sending part
replaced
by the local telephone system of the unknown. The junction is adjusted to
produce, via Path\ 3, the same loudness of received speech sounds as the
NOSFER with its attenuator set at 25\ dB. If\ \fIx\fR\d3\uis the required
setting in Path\ 3, the sending loudness rating (SLR) is given
by\ (\fIx\fR\d2\u\ \(em\ \fIx\fR\d3\u)\ dB.
.bp
.RT
.sp 1P
.LP
2.2.3
    \fIReceiving loudness rating\fR
.sp 9p
.RT
.PP
Path 4 in Figure 2/P.76 shows the IRS with its receiving part
replaced by the local telephone system of the unknown.
.PP
The junction is adjusted to produce via Path\ 4 the same loudness of
received speech sounds as the NOSFER with its attenuator set at 25\ dB.
If\ \fIx\fR\d4\uis the required setting in Path\ 4, the receiving loudness
rating (RLR) is given by (\fIx\fR\d2\u\ \(em\ \fIx\fR\d4\u)\ dB.
.RT
.sp 1P
.LP
2.2.4
    \fIJunction loudness rating\fR
.sp 9p
.RT
.PP
Path 5 in Figure 2/P.76 shows the IRS with its junction replaced by the
unknown chain of circuits as located in Path\ 1 of Figure\ 2/P.76 between\
JS and\ JR. The arrangement for introducing transmission loss, independent
of
frequency, must be provided as was required in Path\ 1. The additional
loss is adjusted to produce, via Path\ 5, the same loudness of received
speech as the
NOSFER with its attenuator set at 25\ dB. If\ \fIx\fR\d5\uis the required
additional loss in Path\ 5, the junction loudness rating is given by
(\fIx\fR\d2\u\ \(em\ \fIx\fR\d5\u)\ dB.
.RT
.sp 2P
.LP
2.3
    \fIConditions under which loudness ratings are determined\fR
.sp 1P
.RT
.sp 1P
.LP
2.3.1
    \fIGeneral\fR
.sp 9p
.RT
.PP
The loudness of received speech sounds depends upon certain factors that
are not well defined under practical conditions of use, but must be
defined as precisely as possible to obtain accurately reproducible loudness
ratings. Clearly, as shown in Figure\ 1/P.76, the loudness rating is largely
governed by the characteristics of the mouth\(hyto\(hyear path. This path
can be made precise by defining a \fImouth reference point\fR at which
the sound
pressure\ \fIp\fR\d\fIM\fR\uof speech emitted by the talker is measured
or referred, and an ear reference point at which to measure or to which
to refer the sound
pressure\ \fIp\fR\d\fIE\fR\uof speech reproduced by the earphone. These
points can be
chosen in a fairly arbitrary manner and this becomes important when loudness
ratings are to be determined objectively; suitable definitions for such
purposes are given in Recommendation\ P.64 which deals with measurement of
sending and receiving sensitivity/frequency characteristics.
.PP
It is essential, however, to define vocal level, speaking distance,
microphone position and listening conditions which govern the fit of the
earphone to the ear. These are indicated in Figure\ 1/P.76. The essential
features that define the conditions under which loudness ratings are determined
are indicated in Table\ 1/P.76.
.PP
Some remarks on the items listed in Table\ 1/P.76 are given
below.
.RT
.sp 1P
.LP
2.3.2
    \fIIntermediate reference system\fR
.sp 9p
.RT
.PP
The intermediate reference system is defined in
Recommendation\ P.48. It has been chosen with the following in mind:
.RT
.LP
    a)
     It shall correspond approximately, as far as the shapes of sending and
receiving frequency character
istics are concerned,
with those of national sending and receiving systems in
use at present and likely to be used in the near future.
For this reason the frequency bandwidths for sending and
receiving parts are confined to the nominal range
300\(hy3400\ Hz
.FS
The IRS is specified for the range 100\(hy5000\ Hz (see
Recommendation\ P.48). The nominal range 300\(hy3400\ Hz specified is intended
to be consistent with the nominal 4\ kHz spacing of FDM systems, and should
not be
interpreted as restricting improvements in transmission quality which might
be obtained by extending the transmitted frequency bandwidth.
.FE
.
.LP
    b)
     The absolute sensitivity has been chosen to reduce as much as possible
changes in values from reference equivalents to
loudness ratings.
.LP
    c)
    In external form its handsets are similar to conventional
handsets used in actual telephone connections.
.bp
.LP
.ce
\fBH.T. [T1.76]\fR
.ce
TABLE\ 1/P.76
.ce
\fBConditions under which loudness ratings are determined\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(18p) | cw(156p) | cw(54p) .
No.    Item specified    Specification
_
.T&
cw(18p) | lw(156p) | lw(54p) .
1    Intermediate reference system    Recommendation P.48
_
.T&
cw(18p) | lw(156p) | lw(54p) .
2    Vocal level of speaker     {
As Recommendation P.72 (Red Book)
 }
_
.T&
cw(18p) | lw(156p) | lw(54p) .
3     {
Level of received speech sounds at which loudness is judged constant
 }    NOSFER set at 25 dB
_
.T&
cw(18p) | lw(156p) | lw(54p) .
4     {
Handset position relative to talker's mouth
 }    See Annex A
_
.T&
cw(18p) | lw(156p) | lw(54p) .
5    Direction of speech    Head erect
_
.T&
cw(18p) | lw(156p) | lw(54p) .
6     {
Handset arrangement for listening
 }    See \(sc 2.3.7
_
.T&
cw(18p) | lw(156p) | lw(54p) .
7     {
Conditioning of carbon microphones
 }    Recommendation P.75
_
.TE
.nr PS 9
.RT
.ad r
\fBTableau 1/P.76 [T1.76], p. 3\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
2.3.3
    \fIVocal level of speaker\fR
.sp 9p
.RT
.PP
The vocal level at which speech is emitted from the speaker's mouth conforms
to that in use for determining reference equivalents and is defined in
Recommendation\ P.72 \fIRed Book\fR . This approximates the level actually
used by
customers under good transmission conditions. It is defined in terms of the
speech level at the output of the NOSFER sending system.
.RT
.sp 1P
.LP
2.3.4
    \fIListening level\fR
.sp 9p
.RT
.PP
The level of received speech sounds at which loudness is judged
constant is defined by the vocal level (see\ \(sc\ 2.3.3\ above) and the
setting
(25\ dB) of NOSFER against which all the speech paths shown in Figure\ 2/P.76
are adjusted. This corresponds to a fairly comfortable listening level
of the same order as that commonly experienced by telephone users.
.RT
.sp 1P
.LP
2.3.5
    \fIHandset position\fR
.sp 9p
.RT
.PP
The position of the telephone handset relative to the talker's mouth is
defined in Annex\ A to this Recommendation. It is intended to approximate
fairly well the position used by customers under real telephone connections.
The definition covers not only the distance between lips and mouthpiece but
also the attitude of the microphone relative to the horizontal axis through
the centre of the lips. It is defined in such a way that the
lips\(hyto\(hymouthpiece distance becomes greater as the length of a handset is
increased.
.RT
.sp 1P
.LP
2.3.6
    \fIDirection of speech\fR
.sp 9p
.RT
.PP
The speaker shall hold his head erect and it will be assumed
that speech is emitted horizontally from his mouth.
.RT
.sp 1P
.LP
2.3.7
    \fIHandset arrangement for listening\fR
.sp 9p
.RT
.PP
The listener shall hold the handset in his hand with the earphone placed
comfortably against his ear.
.bp
.RT
.sp 1P
.LP
2.3.8
    \fIConditioning of carbon microphones\fR
.sp 9p
.RT
.PP
Telephone handsets with carbon microphones usually require
to be conditioned. This shall be done in accordance with
Recommendation\ P.75.
.RT
.sp 2P
.LP
\fB3\fR     \fBSidetone loudness ratings\fR
.sp 1P
.RT
.PP
It is necessary to examine the effects of telephone sidetone on the subscriber
when considered both as a talker and as a listener. In each case,
studies have shown that control of the higher frequencies (>1000\ Hz) in the
telephone sidetone path is important to preserve good conversational conditions
in high\(hylevel room noise and/or on long\(hyline connections. Sidetone
loudness
rating methods that place more weight on these higher frequencies are therefore
required; suitable methods are described below.
.RT
.sp 2P
.LP
3.1
    \fITalker Sidetone\fR
.sp 1P
.RT
.sp 1P
.LP
3.1.1
    \fIDefinition of\fR
\fIsidetone masking rating (STMR)\fR
.sp 9p
.RT
.PP
When a telephone subscriber speaks, his own voice reaches his ear by several
paths (see\ Figure\ 3/P.76):
.RT
.LP
    a)
    through the telephone set circuit from microphone to
earphone due to mismatch of the hybrid balance impedance within
the set and the line impedance;
.LP
    b)
    through the mechanical path within the human head;
.LP
    c)
    through the acoustic path to the ear and involving leakage
at the earcap and human ear interface;
.LP
    d)
    through the mechanical path along a handset handle [although
this may be measured in fact as a contribution to
a)\ above].
.LP
.rs
.sp 17P
.ad r
\fBFigure 3/P.76, p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
Determination of these sidetone paths will usually resolve into
two main measurements, a)\ +\ d) and b)\ +\ c). Each is referred to the speech
signal at the mouth reference point (MRP) and the measurement made at the
ear reference point (ERP).
.PP
Thus \fIL\fR\d\fIM\fR\\d\fIE\fR\\d\fIS\fR\\d\fIT\fR\uis the loss from the
mouth to ear (MRP to
ERP) of the telephone sidetone path, and \fIL\fR\d\fIM\fR\\d\fIE\fR\\d\fIH\fR\\d\fIS\fR\uis
the loss from mouth to ear (MRP to ERP) of the human sidetone path.
.bp
.PP
\fINote\fR \ \(em\ Recommendation P.64, \(sc\ 8 describes a method for the
measurement of \fIS\fR\d\fIm\fR\\d\fIe\fR\\d\fIS\fR\\d\fIT\fR\u, the sidetone
sensitivity/frequency
characteristic of a telephone set using the artificial mouth and ear, from
which an estimate of \fIS\fR\d\fIM\fR\\d\fIE\fR\\d\fIS\fR\\d\fIT\fR\uusing
the human mouth and ear may be obtained by adding correction \fIL\fR\d\fIM\fR\uand
\fIL\fR\d\fIE\fR\uas explained in the text.
Thus:
\v'6p'
.RT
.sp 1P
.ce 1000
\fIL\fR\d\fIM\fR\\d\fIE\fR\\d\fIS\fR\\d\fIT\fR\u= \(em\fIS\fR\d\fIM\fR\\d\fIE\fR\\d\fIS\fR\\d\fIT\fR\uin
dB
.ce 0
.sp 1P
.PP
.sp 1
\fIL\fR\d\fIM\fR\\d\fIE\fR\\d\fIS\fR\\d\fIT\fR\uand \fIL\fR\d\fIM\fR\\d\fIE\fR\\d\fIH\fR\\d\fIS\fR\uare
each usually
measured at a number of frequencies in the ISO range of 1/3rd octave frequencies,
typically at least 200 to 4000\ Hz. Where complex signals are used (for
example, during the measurement of \fIL\fR\d\fIM\fR\\d\fIE\fR\\d\fIH\fR\\d\fIS\fR\uthe
subjects' speech signals were used), spectrum density measurements must
be made.
.PP
Studies completed so far have indicated that for talker sidetone at
least, the rating method which correlates best with subjective effects of
sidetone is one which takes into account the human sidetone signal as a
masking threshold, i.e.\ sidetone masking rating (STMR).
.RT
.sp 2P
.LP
3.2
    \fIListener sidetone\fR
.sp 1P
.RT
.sp 1P
.LP
3.2.1
    \fIDefinition of listener sidetone rating (LSTR)\fR
.sp 9p
.RT
.PP
When the subscriber is listening, any room noise may reach the ERP through
paths a) and c) of Figure\ 3/P.76. It is the high frequencies of local
room noise which are most likely to mask the low\(hylevel consonants of
a received signal. The STMR method described in \(sc\ 3.1 has the effect
of controlling
\fIL\fR\d\fIm\fR\\d\fIe\fR\\d\fIS\fR\\d\fIT\fR\umore effectively at frequencies
higher than 1000\ Hz.
Control of these frequencies is also important for room noise sidetone.
This is because the low frequencies of a received signal at the earphone
will be
masked by low frequency room noise (leaking past the earcap) in much the
same way as the talker's speech signal heard via the telephone sidetone
path
(\fIL\fR\d\fIm\fR\\d\fIe\fR\\d\fIS\fR\\d\fIT\fR\u) is masked by that heard
via the human sidetone
path (\fIL\fR\d\fIM\fR\\d\fIE\fR\\d\fIH\fR\\d\fIS\fR\u).
.PP
Studies have shown that if the room noise sidetone path
(\fIL\fR\d\fIR\fR\\d\fIN\fR\\d\fIS\fR\\d\fIT\fR\u) is determined as described
in Recommendation\ P.64, and used in the STMR rating method, the resulting
ratings correlate well with the subjective effects of room noise heard
over the telephone sidetone path.
The explanation of this is that the composite room noise signal arriving
at the listener's ear and which performs a masking function on the received
speech
signals is believed to have a characteristic very similar to that of
\fIL\fR\d\fIM\fR\\d\fIE\fR\\d\fIH\fR\\d\fIS\fR\u.
.PP
Thus LSTR is defined as that attenuation that must be inserted into
the IRS (Recommendation\ P.48) to give an equivalent loudness to
\fIL\fR\d\fIR\fR\\d\fIN\fR\\d\fIS\fR\\d\fIT\fR\uwhen similarly taking \fIL\fR\d\fIM\fR\\d\fIE\fR\\d\fIH\fR\\d\fIS\fR\uinto
account as a masking threshold (Recommendation\ P.79).
.RT
.sp 1P
.LP
3.2.2
    \fIDetermination of LSTR\fR
.sp 9p
.RT
.PP
To calculate LSTR it is necessary to determine the sensitivity
\fIS\fR\d\fIR\fR\\d\fIN\fR\\d\fIS\fR\\d\fIT\fR\u | (where \fIS\fR\d\fIR\fR\\d\fIN\fR\\d\fIS\fR\\d\fIT\fR\u\
=\ \(em\fIL\fR\d\fIR\fR\\d\fIN\fR\\d\fIS\fR\\d\fIT\fR\u) using a method
such as that described in Recommendation\ P.64, or in the
\fIHandbook on\fR \fITelephonometry\fR , Section\ 3, and making use of
the calculation
procedure given in Recommendation\ P.79.
.PP
\fIS\fR\d\fIR\fR\\d\fIN\fR\\d\fIS\fR\\d\fIT\fR\u, room noise sidetone sensitivity,
will, in general, not have the same value as \fIS\fR\d\fIm\fR\\d\fIe\fR\\d\fIS\fR\\d\fIT\fR\u,
talker sidetone sensitivity, since the sensitivity of the handset microphone
may not be the
same
for random incidence signals as for a point source close to the diaphragm
(less that\ 5\ cm). Usually room noise arrives at the microphone at lower
levels than speech and this can result in different sensitivity values,
particularly where carbon microphones are present.
.PP
The difference between \fIS\fR\d\fIR\fR\\d\fIN\fR\\d\fIS\fR\\d\fIT\fR\u |
and \fIS\fR\d\fIm\fR\\d\fIe\fR\\d\fIS\fR\\d\fIT\fR\u | for a given telephone
will usually be constant for different line conditions
provided that it is operating in a linear part of its characteristic, and/or
the room noise level is constant. This difference is \(*D\fI\fI\d\fIS\fR\\d\fIm\fR\u,
(or DELSm), and is explained further in Recommendations\ P.10 and P.64,
\(sc\ 9. The use of \(*D\fI\fI\d\fIS\fR\\d\fIm\fR\ucan be convenient where
values of \fIS\fR\d\fIm\fR\\d\fIe\fR\\d\fIS\fR\\d\fIT\fR\uare
known, to determine \fIS\fR\d\fIR\fR\\d\fIN\fR\\d\fIS\fR\\d\fIT\fR\ufor
the purpose of calculating LSTR.
Thus:
\v'6p'
.RT
.sp 1P
.ce 1000
\fIS\fR\d\fIR\fR\\d\fIN\fR\\d\fIS\fR\\d\fIT\fR\u= \fIS\fR\d\fIm\fR\\d\fIe\fR\\d\fIS\fR\\d\fIT\fR\u+
\(*D\fI\fI\d\fIS\fR\\d\fIm\fR\u
.ce 0
.sp 1P
.LP
.sp 1
.PP
Normally \(*D\fI\fI\d\fIS\fR\\d\fIm\fR\u | is negative, thus telephones
that have a
more negative value for \(*D\fI\fI\d\fIS\fR\\d\fIm\fR\u | will have a lower
value of
\fIS\fR\d\fIR\fR\\d\fIN\fR\\d\fIS\fR\\d\fIT\fR\uand perform better in noisy
room conditions from the point of view of sidetone.
.bp
.PP
For telephone sets with linear microphones, \(*D\fI\fI\d\fIS\fR\\d\fIm\fR\u |
can vary over several decibels, typical values ranging from\ \(em1.5 to
\(em4\ dB. For carbon
microphones, measurement values have been reported as low as \(em15\ dB at some
frequencies, but typical average values probably lie in the region of \(em8\
dB for a room noise of 60\ dBA. For some sets with linear microphones,
the gain is
intentionally not constant over their input/output characteristics in order
to improve performance in noisy conditions. (See also Recommendation\ G.111,
Annex\ A on the subject of\ \(*D\fI\fI\d\fIS\fR\\d\fIm\fR\u).
.PP
\fINote\fR \ \(em\ Supplement\ No.\ 11 provides information on some of
the effects of sidetone on transmission performance quantified over a number
of study
periods.
.RT
.ce 1000
ANNEX\ A
.ce 0
.ce 1000
(to Recommendation P.76)
.sp 9p
.RT
.ce 0
.ce 1000
\fBDefinition of the\fR
\fBspeaking position for measuring\fR
.sp 1P
.RT
.ce 0
.ce 1000
\fBloudness ratings of handset telephones\fR
.ce 0
.PP
This annex describes the speaking position which should be
used to measure the
sensitivities of commercial telephone sets
(by the method described in Recommendation\ P.64) for the determination
of loudness
ratings.
.sp 1P
.RT
.PP
A.1
The definition of a speaking position falls into two parts: description
of the relative positions of mouth opening and ear\(hycanal opening on
an \fIaverage\fR human head; and description of the angles that define
the attitude in space of telephone handsets held to such a head. For any
given telephone
handset, these descriptions together describe the relative special disposition
of the microphone opening and the talker's lips, and hence the direction
in
which speech sound waves arrive at the mouthpiece and the distance they have
travelled from a \fIvirtual point source\fR .
.sp 9p
.RT
.PP
The relative positions of the centre of the lips and that of the ear canal
can be described in terms of a distance \(*d\ and an angle\ \(*a as shown
in Figure\ A\(hy1/P.76. Point\ R in that figure represents the centre of
a guard ring located at the reference equivalent speaking position in accordance
with
Recommendation\ P.72, \fIRed Book\fR . Position\ A is that used to determine
ratings by the articulation method defined in Recommendation\ P.45, \fIOrange
Book\fR .
Averages of lip positions of\ 4012 subjects in the People's Republic of China
cluster round the point\ A (see Recommendation\ P.35).
.LP
.rs
.sp 19P
.ad r
\fBFigure A\(hy1/P.76, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
A second angle is required to define the direction in which speech is emitted
from the mouth into the mouthpiece of the microphone. In former
Recommendations\ P.45 and\ P.72 reference is made to an angle \(*b, but
this does
not lie in the plane of symmetry of the handset, so it is more convenient to
use an angle\ \(*g, which describes the vertical projection of the direction of
speech on this plane.
.PP
A.2
The position of the centre of the lips as defined by A in
Figure\ A\(hy1/P.76 is used also to define the new speaking position, but two
additional angles must also be defined, namely: the earphone rotational
angle\ \(*F and the handset rotational angle\ \(*H. Earphone rotation is
considered about an
axis through the centre of the ear\(hycap (YY\ in Figure\ A\(hy1/P.76); handset
rotation is taken about a longitudinal axis of the handset (XX\ in
Figure\ A\(hy1/P.76); both angles are zero when the plane of symmetry
of the handset is horizontal. Naturally, the earphone rotational angle is
positive when the handle is pointed downwards away from the earphone and the
handset rotational angle is positive in the sense that the upper part of the
earphone is moved farther from the medial plane of the head.
.sp 9p
.RT
.PP
The new speaking position is described by the following values for the
distance and angles defined above:
\v'6p'
.sp 1P
.ce 1000
\(*a\ =\ 22\(de,\ \(*g\ =\ 12.9\(de,\ \(*d\ =\ 136 mm,\ \(*F\ =\ 39\(de\
and\ \(*H\ =\ 13\(de
.ce 0
.sp 1P
.PP
.sp 1
The angle \(*g cannot be determined very precisely and is not
convenient for use when setting up a handset for test in front of an artificial
mouth. The semi\(hyinteraural distance \(*e" may be used in its place,
and for the new speaking position \(*e\ =\ 77.8\ mm.
.PP
For any test jig, the manufacture tolerance should be within
\(+- | .5\uo\d for the angles defined above.
.RT
.PP
A.3
The foregoing description of the speaking position has
shown the complexities of expressing the relative location of the ear reference
point and the guard\(hyring centre, and the relative orientation of the
earphone axis and the guard\(hyring axis. It is often more convenient,
particularly in
terms of constructing and setting up handset jigs, to express the position
of the ear reference point
.FS
See Recommendation\ P.64 for definition of ear
reference point.
.FE
and the direction of the earphone axis with respect to
the lip\(hyring. This is easier since the axis of the guard\(hyring is
horizontal as would be the axis of an associated artificial mouth.
.sp 9p
.RT
.PP
A.4
Use has been made of a vector analysis method to determine the orthogonal
coordinates of the handset ear\(hycap relative to the lip position when
the handset is mounted in the LR guard ring position. It is necessary to
define a set of cartesian axes with origin at the centre of the lips (or
equivalent lip position of an artificial voice
) as follows:
.sp 9p
.RT
.LP
    x\(hyaxis:
    horizontal axis of the mouth, with positive direction
into the mouth;
.LP
    y\(hyaxis:
    horizontal, perpendicular to the x\(hyaxis, with positive
direction towards the side of the mouth on which the
handset is held;
.LP
    z\(hyaxis:
    vertical, with positive direction upwards.
.PP
The
ear reference point
is defined by the vector:
\v'6p'
.sp 1P
.ce 1000
(86.5, 77.8, 70.5) mm.
.ce 0
.sp 1P
.LP
.sp 1
.PP
The handset is mounted so that the ear reference point lies at the intersection
of the axis of the ear\(hycap with a plane in space on which the
ear\(hycap can be considered to be resting. With some shapes of handset, this
definition is not adequate; in such cases the position of the ear reference
point relative to the handset should be clearly stated.
.PP
The orientation of the handset is defined by vectors normal to the
plane of the ear\(hycap and the plane of symmetry of the handset:
.PP
Unit vector normal to plane of the ear\(hycap:
\v'6p'
.RT
.sp 1P
.ce 1000
\(+- (0.1441, \(em0.974, 0.1748)
.ce 0
.sp 1P
.PP
.sp 1
Unit vector normal to plane of symmetry of the handset:
\v'6p'
.sp 1P
.ce 1000
\(+- (0.6519, \(em0.0394, \(em0.7572).
.ce 0
.sp 1P
.LP
.sp 1
.bp
.PP
When using an artificial voice, the equivalent lip position must be used
as the datum; this is not normally the same as the plane of the orifice
of the artificial mouth.
.PP
Alternatively, it can be convenient to define the speaking
position in terms of axes with the origin at the ear reference point. These
are defined as follows:
.RT
.LP
    x\(hyaxis:
    axis of ear\(hycap with positive direction away from
earphone;
.LP
    y\(hyaxis:
    line of intersection of the plane of symmetry of the
handset with the ear\(hycap plane, with positive
direction towards the microphone;
.LP
    z\(hyaxis:
    normal to the plane of symmetry of the handset with
positive direction obliquely upwards.
.PP
The
lip\(hyring centre
is defined by the vector:
\v'6p'
.sp 1P
.ce 1000
(50.95, 126.10, 0) mm.
.ce 0
.sp 1P
.LP
.sp 1
.PP
The
orientation of the lip\(hyring
is defined by a unit
vector along its axis:
\v'6p'
.sp 1P
.ce 1000
\(+- | 0.1441, \(em0.7444, \(em0.6250)
.ce 0
.sp 1P
.LP
.sp 1
and the
orientation of the handset
is defined by specifying the
vertical by the unit vector:
\v'6p'
.sp 1P
.ce 1000
\(+- | 0.1748, \(em0.6293, +0.7572).
.ce 0
.sp 1P
.PP
.sp 1
\fINote\fR \ \(em\ The speaking position defined above differs from the
special guard\(hyring position
in the values of \(*F\ (=\ 37\(de) and \(*H\ (=\ 19\(de). It has been found
that altering the handset position from the special
guard\(hyring position to the loudness rating guard\(hyring position described
above affects sensitivity measurements to a negligible extent.
\v'6p'
.ce 1000
ANNEX\ B
.ce 0
.ce 1000
(to Recommendation P.76)
.sp 9p
.RT
.ce 0
.ce 1000
\fBExplanations of certain terminology\fR
.sp 1P
.RT
.ce 0
.LP
.rs
.sp 16P
.ad r
\fBFigure B\(hy1/P.76, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
The terminology of Figure\ B\(hy1/P.76 applies to parts of a telephone
connection according to Recommendations\ G.101\ [3], G.111\ [4], G.121\
[5] and
CCITT manuals.
.PP
\fINote\fR \ \(em\ In the present Recommendation the word \*Qjunction\*U
is used in a special sense to denote \*Qchain of circuits interconnecting
the two local
systems\*U and the \*Qjunction attenuator\*U used in laboratory tests for
determination of loudness ratings.
.RT
.sp 2P
.LP
    \fBReferences\fR
.sp 1P
.RT
.LP
[1]
    CCITT \(em Question 19/XII, Contribution COM XII\(hyNo.\ 1, Study Period
1985\(hy1988, Geneva,\ 1985.
.LP
[2]
    CCITT Manual \fITransmission planning of switched telephone networks\fR ,
Chapter\ I, Annex\ 1, ITU, Geneva,\ 1976.
.LP
[3]
    CCITT Recommendation \fIThe transmission plan\fR , Vol.\ III,
Rec.\ G.101.
.LP
[4]
    CCITT Recommendation
\fILoudness ratings (LRs) in an international connection\fR , Vol.\ III,
Rec.\ G.111.
.LP
[5]
    CCITT Recommendation
\fILoudness ratings (LRs) of national systems\fR , Vol.\ III, Rec.\ G.121.
.LP
.sp 8
.sp 2P
.LP
\fBRecommendation\ P.78\fR
.RT
.sp 2P
.ce 1000
\fBSUBJECTIVE\ TESTING\ METHOD\ FOR\ DETERMINATION\ OF\ LOUDNESS\ RATINGS\fR
.EF '%    Volume\ V\ \(em\ Rec.\ P.78''
.OF '''Volume\ V\ \(em\ Rec.\ P.78    %'
.ce 0
.sp 1P
.ce 1000
\fBIN\ ACCORDANCE\ WITH\ RECOMMENDATION\ P.76\fR
.ce 0
.sp 1P
.ce 1000
\fI(amended at Malaga\(hyTorremolinos, 1984, Melbourne, 1988)\fR
.sp 9p
.RT
.ce 0
.sp 1P
.LP
    \fBPreface\fR
.sp 1P
.RT
.PP
This Recommendation describes a subjective testing method which has been
found suitable for its purpose by use in the CCITT Laboratory. It can also
be used in other laboratories. Provided that the Intermediate Reference
System (IRS) used complies with the requirements of Recommendation\ P.48
and that
other requirements given in Recommendation\ P.76 are adhered to, the loudness
ratings obtained by using the method given in the present Recommendation
can be used for forwarding the study of Question\ 19/XII [1] (Recommended
values of
loudness rating). The present Recommendation, together with
Recommendations\ P.76 and\ P.48, provides a definition of loudness ratings
which can be used for planning.
.RT
.sp 2P
.LP
    \fBSummary\fR
.sp 1P
.RT
.PP
This Recommendation contains the essential particulars for defining the
method for determining loudness ratings in accordance with
Recommendation\ P.76 when use is made of subjects performing equal loudness
balances. Details are included concerning the balancing method, choice of
subjects, speech material, design of experiment, method of analysis and
presentation of results.
.PP
Study is continuing under Question\ 8/XII on using a direct\(hybalance
method. A description of this method can be found in Supplement\ No.\ 17.
.bp
.RT
.sp 2P
.LP
\fB1\fR     \fBIntroduction\fR
.sp 1P
.RT
.PP
To compare the calculation of loudness ratings method
(Recommendation\ P.79) a defined method of subjectively determining loudness
ratings is required. This Recommendation deals with all aspects of a test
from selection of operators to the method of analysis and finally presentation
of
results.
.RT
.sp 2P
.LP
\fB2\fR     \fBGeneral\fR
.sp 1P
.RT
.PP
In the subjective comparisons, the Fundamental Reference System
(FRS) is used (although other reference systems are permissible) as the
datum for comparing the following speech paths:
.RT
.LP
    a)
     \fIPath\ 0\fR \ \(em\ The fundamental reference system always provides
the speech path against which each of the others is balanced.
NOSFER set at 25\ dB is used.
.LP
    b)
    \fIPath\ 1\fR \ \(em\ The send end of the test (\*Qunknown\*U) local
telephone circuit connected through the test (\*Qunknown\*U)
junction and an adjustable attenuator to the receive end of the
test (\*Qunknown\*U) local telephone circuit. The adjustable
attenuator must be inserted in such a manner that the impedance
relationships between the three parts of the connection (send
end, junction and receive end) are not disturbed.
.LP
    c)
     \fIPath\ 2\fR \ \(em\ The send end of the intermediate reference system
connected through an adjustable attenuator to the receive end of
the intermediate reference system.
.LP
    d)
    \fIPath\ 3\fR \ \(em\ The send end of the test (\*Qunknown\*U) local
telephone circuit connected through an adjustable attenuator to
the receive end of the IRS.
.LP
    e)
    \fIPath\ 4\fR \ \(em\ The send end of the IRS connected through an
adjustable attenuator to the receive end of the test (\*Qunknown\*U)
local telephone system.
.LP
    f
)
     \fIPath\ 5\fR \ \(em\ The send end of the IRS connected through the test
(\*Qunknown\*U) junction and an adjustable attenuator to
the receive end of the IRS. The adjustable attenuator must be
inserted in such a manner that the impedance relationships
between the three parts of the connection (send end, junction and
receive end) are not disturbed.
.PP
In these subjective comparisons, the junction of the fundamental reference
system is fixed, i.e.\ the level of speech sounds received via the
fundamental reference system is kept constant, the
loudness balance
being obtained by the so\(hycalled \*Qmargin\*U method, and the balance
attenuator
being that inserted in the telephone (or IRS) path being tested.
.PP
The
speaking position
used with both the IRS and the test
telephone sets should be as defined in Annex\ A to Recommendation\ P.76.
.PP
Figure 1/P.78 shows the composition of the telephone paths to be
compared. The balances should be conducted using the vocal level defined in
Recommendation\ P.72.
.PP
The loudness ratings relative to the IRS as defined in
Recommendation\ P.76 are:
.RT
.LP
    OLR
    =\ \fIx\fR\d2\u\ \(em\ \fIx\fR\d1\u
.LP
    SLR
    =\ \fIx\fR\d2\u\ \(em\ \fIx\fR\d3\u
.LP
    RLR
    =\ \fIx\fR\d2\u\ \(em\ \fIx\fR\d4\u
.LP
    JLR
    =\ \fIx\fR\d2\u\ \(em\ \fIx\fR\d5\u
.PP
It is not necessary to include all the paths indicated above in
every experiment. Paths\ 0 and\ 2 are essential but addition of only 3
and 4 is sufficient to determine sending and receiving loudness ratings
of a local
telephone circuit. Paths\ 0, 2 and 5 are required to determine a junction
loudness rating. Path\ 1 is usually required only when it is derived to
verify additivity of loudness ratings, namely that:
\v'6p'
.sp 1P
.ce 1000
OLR\ =\ SLR\ +\ JLR\ +\ RLR
.ce 0
.sp 1P
.LP
.sp 1
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 1/P.78, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 2P
.LP
\fB3\fR     \fBExperiment design\fR
.sp 1P
.RT
.PP
To have confidence in results requires the correct testing
procedures to be followed, coupled with the correct experiment design. The
procedure should be prepared such that no ambiguity can exist.
.PP
The following points must be considered in the design:
.RT
.LP
    a)
    The experiment should be designed in such a way that all
uncontrolled influences operate at random, e.g.\ slight
day\(hyto\(hyday drift of subjects and/or measuring equipment;
.LP
    b)
    If more balances are required than can be comfortably
completed in one day, then the experiment must be designed such
that equal numbers of each type of system are completed each
day;
.LP
    c)
    The operators who start a test should always be the same
throughout the test [2];
.LP
    d)
     A minimum of 12 operator\(hypair combinations is suggested with a maximum
of 20. Twelve operator\(hypair combinations can be arrived
at from two crews of 3 (see Table\ 1a/P.78) or one crew of 4 and
18\ operator\(hypair combinations can be arrived at from one crew
of\ 6 (see Table\ 1b/P.78) and 20\ operator\(hypair combinations from
one crew of\ 5 (see Table\ 2a/P.78).
.LP
    \fINote\fR \ \(em\ One crew of\ 6 giving 30\ operator\(hypair
combinations (see Table\ 2b/P.78) produces a larger test for only
slightly more precision than the previously mentioned crew sizes;
.LP
.rs
.sp 32P
.ad r
\fBTable 1a\(hyb/P.78 et 2a\(hyb/P.78 [T1.78], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
    e)
    When using two crews of 3, one can use both crews
interleaved but it is generally more practical to separate the crews and use
test crew\ 1 before crew\ 2. Members should not be used in both
crews as it causes a bias and complicates the analysis;
.LP
    f
)
    All operator\(hypair combinations should be tested in
rotation, where practical, such that each operator takes a turn as
talker, then listener and then has a break;
.LP
    g)
    The design of the experiment should eliminate any effect
that could be attributed to the order of presentation. That is to say
that all systems should be in a randomized order. To illustrate
this point two examples are as follows:
.LP
    \fIExample\ 1\fR
.LP
    If one type of loudness rating is required, with a given
combination of telephone set and circuit condition, then
the experiment design must allow for any effect associated with
order of presentation for each operator\(hypair combination. An
example is shown in Table\ 3/P.78.
.LP
     \fINote\fR \ \(em\ However, if a laboratory has found with sufficient
evidence that this method of design is not necessary, then a simplified
design may be used.
.LP
.sp 2
.ce
\fBH.T. [T2.78]\fR
.ce
TABLE\ 3/P.78
.ce
\fBExample to illustrate the elimination of order of presentation
.ce
effect\fR
.ce
\fBfor one type of loudness rating\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(54p) | cw(54p) | cw(24p) | cw(24p) | cw(24p) .
Operator\(hypairs    Talker Listener    A  B    B  C    C  A
_
.T&
cw(54p) | cw(54p) | cw(24p) | cw(24p) | cw(24p) .
Circuits    \(*a \(*a` \(*b \(*b`    3 2 1 4    1 3 4 2     {
2
4
3
1
 }
.TE
.LP
Where
.LP
\(*a
=\ path 0 presented before path trajet 2
.LP
\(*a`
=\ path 2 presented before path trajet 0
.LP
\(*b
=\ path 0 presented before path trajet 3
.LP
\(*b`
=\ path 3 presented before path trajet 0
.LP
\fINote\fR
\ \(em\ When it is proven that there is no difference for a given test crew
and set of test conditions, the distinction between the order of path
presentation can be eliminated.
.nr PS 9
.RT
.ad r
\fBTable 3/P.78 [T2.78], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 2
.LP
    \fIExample\ 2\fR
.LP
    Now, if more than one type of loudness rating is made or
more than one telephone set is used, then there need only be one
balance of path\ 2 against path\ 0 and vice\(hyversa per
operator\(hypair combination for any experiment, but this must
be randomized within the experiment. An example is shown
in Table\ 4/P.78.
.bp
.ce
\fBH.T. [T3.78]\fR
.ce
TABLE\ 4/P.78
.ce
\fBExample to illustrate the elimination of order of presentation
.ce
effect\fR
.ce
\fBfor two type of loudness rating\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(54p) | cw(54p) | cw(24p) | cw(24p) | cw(24p) .
Operator\(hypairs    Talker Listener    A  B    B  C    C  A
_
.T&
cw(54p) | cw(54p) | cw(24p) | cw(24p) | cw(24p) .
Circuits     {
\(*a
\(*a`
\(*b
1
\(*b`
1
\(*b
2
\(*b`
2
 }    3 5 1 6 2 4    1 4 2 5 6 3     {
2
6
5
3
4
1
\(*b
1, \(*b`
 }
.TE
.LP
1\ =\ have, for example, 0 km of subscriber's cable
.LP
\(*b
2, \(*b`
2\ =\ have, for example, 6 km of subscriber's cable.
.LP
 }
_
.TE
.nr PS 9
.RT
.ad r
\fBTable 4/P.78 [T3.78], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 1
.PP
Some experiment designs can be found in Annex\ A.
.sp 2P
.LP
\fB4\fR     \fBSelection of crew members and speech material\fR
.sp 1P
.RT
.PP
Requirements for the selection of crew members including
audiometric testing
of subjects, as well as the speech material used by the crew for subjective
tests, can be found in Annex\ B.
.RT
.sp 2P
.LP
\fB5\fR     \fBCalibration of the IRS\fR
.sp 1P
.RT
.PP
It is most important that the calibration of the IRS is made before every
test so that any small change in SLR and RLR can either be compensated
for in the results or the sensitivity can be changed before the test. It is
good experimental practice to check the
sensitivity of the IRS
after
each experiment. The specification of the IRS is found in Recommendation\
P.48 and the description of the calibration procedure is found in
Recommendation\ P.64. The results of the calibration are used to determine
the corrections to the subjective balance results (see\ \(sc\ 9).
.RT
.sp 2P
.LP
\fB6\fR     \fBCircuit arrangements\fR
.sp 1P
.RT
.PP
Figure 2a)/P.78 shows a typical circuit layout for the measurement of SLR
and RLR. Figures\ 2b)/P.78 and\ 2c)/P.78 show layouts for the measurement
of JLR and OLR respectively. There is no reason if the experimenter so
wished, why all four types of loudness rating cannot be tested in the same
experiment. This, however, would require extremely intricate switching
arrangements.
.PP
In Figures 2a)/P.78, 2b)/P.78 and 2c)/P.78 the 600 ohm on the second position
of switch\ S1 allows the correct speech level to be set when Path\ 0 is
presented after Path\ 1/2/3/4/5 (see Figure\ 1/P.78). This switch should
be of
the nonlocking type and should be returned to the normal position as soon as
the talker has attained the correct speech level.
.PP
In order to reduce the effect of sidetone on the talker's vocal
level during sending and overall determinations, the acoustic sidetone
path of handset telephones should be disabled. This can be accomplished
by placing the earphone in another identical handset and the electrical
connections made to
the correct terminals on the telephone transmission circuit. The earphone
can then be sealed to an IEC/CCITT artificial ear to give the correct acoustic
loading. A simpler method, used by the Australian Post Office, is to seal
the earphone by means of heavy tape. Although this might not have the correct
acoustic loading, in practice it has been found to have a negligible
effect.
.bp
.RT
.LP
.rs
.sp 47P
.ad r
\fBFigure 2/P.78, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
If the microphone is of the carbon\(hygranule type, then before
each balance the conditioning procedure according to Recommendation\ P.75
should be used.
.PP
In Figures 1/P.78 and 2/P.78 the fundamental reference system, NOSFER,
has been shown but other types such as SETED and METRE\(hyAIR\(hyPATH could
be
used.
.RT
.sp 2P
.LP
\fB7\fR     \fBRecording of information\fR
.sp 1P
.RT
.PP
It is essential that as much information of any test should be
recorded, in such a way that at any time in the future, the information
can be retrieved.
.RT
.sp 1P
.LP
7.1
    \fIDetails of the test\fR
.sp 9p
.RT
.PP
Each test should always include the following
information:
.RT
.LP
    a)
     test No. \(em this should be unique so that one test cannot be confused
with another;
.LP
    b)
    date;
.LP
    c)
    title \(em a brief description of the test;
.LP
    d)
    circuit conditions \(em describe each individual path;
.LP
    e)
    diagram to show switching arrangement;
.LP
    f
)
     crew members \(em name each operator and assign a code, as for example
in Table 5/P.78. Then each operator\(hypair
combination can be denoted by a code e.g.\ A\(hyB.
.LP
.sp 1
.ce
\fBH.T. [T4.78]\fR
.ce
TABLE\ 5/P.78
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(120p) .
Crew members
_
.T&
cw(42p) | cw(78p) .
Code    Operator
_
.T&
cw(42p) | cw(78p) .
A
.T&
cw(42p) | cw(78p) .
B
.T&
cw(42p) | cw(78p) .
C
.T&
cw(42p) | cw(78p) .
D
.T&
cw(42p) | cw(78p) .
E
.T&
cw(42p) | cw(78p) .
F
_
.TE
.nr PS 9
.RT
.ad r
\fBTable 5/P.78 [T4.78], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 1
.sp 1P
.LP
7.2
    \fIIndividual balances\fR
.sp 9p
.RT
.PP
These should always include the \*Qhidden loss\*U attenuation, the
\*Qbalance\*U attenuation and finally the result of the
comparison,\ e.g.
\v'6p'
.RT
.sp 1P
.ce 1000
R\ =\ H\ +\ B
.ce 0
.sp 1P
.LP
.sp 1
where
.LP
    R is the result
.LP
    H is the hidden loss
.LP
    B is the balance
.bp
.sp 2P
.LP
\fB8\fR     \fBAnalysis\fR
.sp 1P
.RT
.PP
For any experiment most information can be obtained from an
analysis of variance. However, sufficient useful information can be derived
using the mean, standard deviation. The method of calculation of these
parameters can be found in Annex\ C.
.RT
.sp 2P
.LP
\fB9\fR     \fBPresentation of results\fR
.sp 1P
.RT
.PP
The results of the test should be presented such that the
important information can be displayed on one form. An example of such
a form is shown in Table\ 6/P.78.
.PP
\fINote\fR \ \(em\ In Tables 6/P.78 to 8/P.78 corrected mean = mean +
correction.
.PP
Worked examples of the use of the form shown in Table\ 6/P.78 are
shown in Tables\ 7/P.78 and\ 8/P.78. The form has been modified to allow
SLR and RLR determinations to be made on a local telephone system including
two line
lengths. Table\ 7/P.78 shows the SLR results and Table\ 8/P.78 the RLR
results.
.RT
.LP
.rs
.sp 39P
.ad r
Blanc
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBTable 6/P.78 (\*`a l'italienne) T5.78, p. 13\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBTable 7/P.78 (\*`a l'italienne) T6.78, p. 14\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBTable 8/P.78 (\*`a l'italienne) T7.78, p. 15\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.ce 1000
ANNEX\ A
.ce 0
.ce 1000
(to Recommendation P.78)
.sp 9p
.RT
.ce 0
.ce 1000
\fBExamples of experiment designs\fR
.sp 1P
.RT
.ce 0
.PP
Tables A\(hy2/P.78, A\(hy3/P.78 and A\(hy4/P.78, give typical designs for
different crew sizes.
.sp 1P
.RT
.PP
As an example, using Table A\(hy2/P.78, the order of balances is as given
in Table A\(hy1/P.78.
.LP
.sp 1
.ce
\fBH.T. [T8.78]\fR
.ce
TABLE\ A\(hy1/P.78
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(60p) | cw(60p) | cw(60p) .
Balance No.    Operator\(hy  pair    Circuit
_
.T&
cw(60p) | cw(60p) | cw(60p) .
 {
\ 1
\ 2
\ 3
\ |
\ |
\ |
13
14
15
\ |
\ |
\ |
25
26
27
\ |
\ |
\ |
71
72
 }     {
BA
CB
DC
\fB\ | fR
\fB\ | fR
\fB\ | fR
BA
CB
DC
\fB\ | fR
\fB\ | fR
\fB\ | fR
BA
CB
DC
\fB\ | fR
\fB\ | fR
\fB\ | fR
AC
DA
 }     {
\(*b
1
\(*a
\(*b
2
|
|
|
\(*b`
1
\(*b
1
\(*b`
2
|
|
|
\(*b
2
\(*b`
2
\(*a
|
|
|
\(*b
1
\(*a`
 }
_
.TE
.nr PS 9
.RT
.ad r
\fBTable A\(hy1/P.78 [T8.78], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 1
.PP
The operator\(hypairs in rotation do all balances in numerical
order starting with \*Q1\*U and finishing with \*Q6\*U.
.PP
Similar tables can be drawn up for a test requiring only one
type of loudness rating where only 4\ circuits are required e.g.\ \(*a, \(*a
`, \(*b  and \(*b
` for a SLR test, where numbers\ 1, 2, 3 and\ 4 would be assigned
respectively in the experiment design.
.PP
For a test involving more circuits the same principles can
be followed assigning as many numbers as there are circuits.
.PP
It may be necessary to improve the validity of results and a
replication of the same experiment design using the same operator\(hypairs
can be made.
.bp
.RT
.ce
\fBH.T. [T9.78]\fR
.ce
TABLE\ A\(hy2/P.78\fR
.ce
\fBDesign for one crew of 4 or two crews of 3\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(42p) | cw(42p) | cw(12p) | cw(12p) | cw(12p) | cw(12p) | cw(12p) | cw(12p) | cw(12p) | cw(12p) | cw(12p) | cw(12p) | cw(12p) | cw(12p) , ^  | c | c | c | c | c | c | c | c | c | c | c | c | c.
 {
One crew of 4
Operator\(hypairs
Two crews of 3
 }    Talker  Listener    B  A    C  B    D  C    A  D    C  A    B  D    A  B    B  C    C  D    D  B    A  C    D  A
    Talker  Listener    B  A    C  B    A  C    C  A    B  C    A  B    E  D    F  E    D  F    F  D    E  F    D  E
_
.T&
cw(42p) | cw(42p) | cw(12p) | cw(12p) | cw(12p) | cw(12p) | cw(12p) | cw(12p) | cw(12p) | cw(12p) | cw(12p) | cw(12p) | cw(12p) | cw(12p) .
Circuits     {
\(*a
\(*a`
\(*b
1
\(*b`
1
\(*b
2
\(*b`
2
 }    4 6 1 2 3 5    1 5 2 4 6 3    3 4 5 6 1 2    2 3 6 5 4 1    6 2 3 1 5 4    5 1 4 3 2 6    3 2 5 4 6 1    6 4 3 2 1 5    1 5 2 3 4 6    5 3 1 6 2 4    4 1 6 5 3 2    2 6 4 1 5 3
_
.TE
.nr PS 9
.RT
.ad r
\fBTable A\(hy2/P.78 [T9.78], p. 17\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 3
.ce
\fBH.T. [T10.78]\fR
.ce
TABLE\ A\(hy3/P.78\fR
.ce
\fBDesign for one crew of 6\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
[Unable to Convert Table]
.nr PS 9
.RT
.ad r
\fBTable A\(hy3/P.78 [T10.78], p. 18\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 3
.ce
\fBH.T. [T11.78]\fR
.ce
TABLE\ A\(hy4/P.78\fR
.ce
\fBDesign for one crew of 5\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.ce
[Unable to Convert Table]
.nr PS 9
.RT
.ad r
\fBTable A\(hy4/P.78 [T11.78], p. 19\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.ce 1000
ANNEX\ B
.ce 0
.ce 1000
(to Recommendation P.78)
.sp 9p
.RT
.ce 0
.ce 1000
\fBSelection of crew members, audiometric testing\fR
.sp 1P
.RT
.ce 0
.ce 1000
\fBof subjects and speech material\fR
.ce 0
.LP
B.1
    \fICrew members\fR
.sp 1P
.RT
.PP
The crew should, wherever possible contain an equal number of both men
and women.
.PP
The following points are a guide for selection:
.RT
.LP
    a)
    Good hearing \(em no operator should exceed a
hearing
loss
of a 15\ dB at all frequencies up to and including 4\ kHz
and no more than 25\ dB at 8\ kHz. This is shown in Figure\ B\(hy1/P.78.
If it is intended that
contra\(hylateral balances
are
required and this necessitates the use of both ears, then the
maximum difference between ears should be \(+- | 0\ dB at all
frequencies. An example of an audiometric testing procedure
of subjects is presented below in \(sc\ B.2;
.LP
    b)
    Clear speech \(em each operator should be free from obvious
speech impediments;
.LP
    c)
    The operator should be able to work harmoniously with other  people;
.LP
    d)
    The operator should be able to make simple arithmetical
calculations;
.LP
    e)
    The operator should be able to talk at a constant level,
with the aid of a meter, after sufficient training;
.LP
    f
)
    The operator must not suffer from claustrophobia as
each operator must, during the test, spend a certain amount of
short\(hyterm solitary confinement;
.LP
    g)
     Regular checks should be made to determine the performance of each operator
as both a talker and as a listener to disclose
any unusual changes. A full description can be found in
Reference\ [3].
.LP
.rs
.sp 20P
.ad r
\fBFigure B\(hy1/P.78, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 2P
.LP
B.2
    \fIAudiometric testing of subjects \(em simple screening procedure [4]\fR
.sp 1P
.RT
.PP
B.2.1
Visual examination of ears for wax, ask if subject has a cold, sinusitus
or any other abnormality.
.sp 9p
.RT
.sp 1P
.LP
B.2.2
    \fIFrequencies of test\fR
.sp 9p
.RT
.PP
125, 250, 500, 1000, 2000, 3000, 4000, 6000, 8000 Hz.
.RT
.sp 1P
.LP
B.2.3
    \fIExample of presentation\fR
.sp 9p
.RT
.PP
1000, 2000, 3000, 4000, 6000, 8000, 125, 250, 500, 1000 Hz.
.PP
\fINote\fR \ \(em\ It is common for the second reading at 1000 Hz to be lower
than the first.
.PP
Follow the above sequence for one ear, then repeat for the other
ear.
.RT
.sp 1P
.LP
B.2.4
    \fIExample of finding threshold:\fR
.sp 9p
.RT
.PP
Start above estimated threshold (say 20 dB hearing loss),
approach in 10\ dB steps until inaudible (no\ response). Return to last
audible level
and descend in 5\ dB steps. Then approach this threshold from below in
5\ dB steps. Signal duration 1 to 2\ seconds.
.PP
Threshold is that value at which two equal responses are
obtained from four successive stimuli.
.RT
.sp 1P
.LP
B.2.5
    \fIRoom noise\fR [5]
.sp 9p
.RT
.PP
Using supra\(hyaural type headsets the maximum permissible levels
in the test room are given in
Table\ B\(hy1/P.78.
.PP
If circum\(hyaural type headsets are used then it is normally
permissible to allow higher levels of noise.
.RT
.LP
.sp 4
.ce
\fBH.T. [T12.78]\fR
.ce
TABLE\ B\(hy1/P.78
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(60p) | cw(60p) .
Octave band    Sound pressure level  (dB)
_
.T&
cw(60p) | cw(60p) .
\ 125    22.0
.T&
cw(60p) | cw(60p) .
\ 250    16.0
.T&
cw(60p) | cw(60p) .
\ 500    18.0
.T&
cw(60p) | cw(60p) .
1000    26.0
.T&
cw(60p) | cw(60p) .
2000    36.0
.T&
cw(60p) | cw(60p) .
3000    39.5
.T&
cw(60p) | cw(60p) .
4000    38.5
.T&
cw(60p) | cw(60p) .
6000    40.0
.T&
cw(60p) | cw(60p) .
8000    34.5
_
.TE
.nr PS 9
.RT
.ad r
\fBTable B\(hy1/P.78 [T12.78], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
B.3
    \fISpeech material\fR
.sp 9p
.RT
.PP
The test phrase or phrases can be either a \*Qnonsense\*U or
\*Qmeaningful\*U phrase. Examples are:
.RT
.LP
    a)
    Joe took father's shoe bench out,
.LP
    b)
     Paris\ \(em\ Bordeaux\ \(em\ Le Mans\ \(em\ Saint\(hyLeu\ \(em\ L\*'eon\
\(em\ Loudun.
.PP
Due consideration should be given to the following points:
.LP
    i)
    The ability of each operator to pronounce the chosen test
phrase or phrases fluently and at a steady speech level. The
sound structure of the native languages of the operators has
therefore a bearing on the choice of test phrase or phrases;
.LP
    ii)
     The phrase or phrases should be chosen so that the agreed measurement
method to control the speech level (i.e.\ deflection
of meter) can give a consistent and readily appreciated
indication of vocal level.
\v'6p'
.ce 1000
ANNEX\ C
.ce 0
.ce 1000
(to Recommendation P.78)
.sp 9p
.RT
.ce 0
.ce 1000
\fBSimplified statistical analysis\fR
.sp 1P
.RT
.ce 0
.LP
C.1
    \fIMean\fR
.sp 1P
.RT
.PP
The mean is obtained by using the following formula:
\v'6p'
.RT
.sp 1P
.ce 1000
\fIx\fR  |
=
@ {  int  \fIx\fR } over { fIn\fR } @
.ce 0
.sp 1P
.LP
.sp 1
C.2
    \fIStandard deviation\fR
.sp 9p
.RT
.PP
It cannot be assumed that the operators are a sample drawn at
random from a population and that the operator\(hypair combinations are
independent of each other. Under these circumstances the standard deviation
must be of the sample and not an estimate of a population.
.PP
The formula for the standard deviation is:
\v'6p'
.RT
.sp 1P
.ce 1000
\(*s =
@ sqrt { {  int  (\fIx\fR~\(em~\fIx\fR~ | ) \u2\d } over { fIn\fR } } @
.ce 0
.sp 1P
.PP
.sp 1
C.3
A more detailed statistical analysis is possible to calculate confidence
intervals as explained in \(sc\ 1.3.4 of the
\fIHandbook on Telephonometry\fR \ [6]. The confidence interval is governed
by the
dispersion between the crew members, the number of crew members and the
arrangement of the experimental design. Typical values in a well\(hyconducted
test are \(+- | \ dB for the arrangements shown in Table 1a/P.78, \(+- | \
dB for Table
1b/P.78, \(+- | \ dB for Table\ 2a/P.78 and \(+- | \ dB for Table\ 2b/P.78.
.sp 9p
.RT
.sp 2P
.LP
    \fBReferences\fR
.sp 1P
.RT
.LP
[1]
    CCITT\ \(em\ Question 19/XII, Contribution COM XII\(hyNo.\ 1, Study Period
1985\(hy1988, Geneva,\ 1985.
.LP
[2]
     \fIThe design and analysis of loudness efficacy measurements\fR , Red\
Book, Vol.\ V, Annex\ 7, ITU, Geneva,\ 1962.
.LP
[3]
    \fIExtract from a study of the differences between results for\fR
\fIindividual crew members in loudness balance tests\fR , Red\ Book, Vol.\
V, Annex\ 6, p.\ 214, ITU, Geneva,\ 1962.
.LP
[4]
    BURNS (W.): Noise and man, \fIMurray\fR , pp. 70\(hy80, 1968
.LP
[5]
    \fIIbid.\fR , pp. 298\(hy300.
.LP
[6]
    CCITT\ \(em\ \fIHandbook on Telephonometry\fR , ITU, Geneva, 1987.
.bp
.sp 2P
.LP
\fBRecommendation\ P.79\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBCALCULATION\ OF\ LOUDNESS\ RATINGS\fR
.EF '%    Volume\ V\ \(em\ Rec.\ P.79''
.OF '''Volume\ V\ \(em\ Rec.\ P.79    %'
.ce 0
.sp 1P
.ce 1000
\fI(Geneva, 1980; amended at Malaga\(hyTorremolinos, 1984, Melbourne, 1988)\fR
.sp 9p
.RT
.ce 0
.sp 1P
.LP
    \fBPreface\fR
.sp 1P
.RT
.PP
The method given in this Recommendation is provisional for the
reason stated in detail below, that its applicability to local telephone
systems containing carbon microphones has not been confirmed beyond doubt.
Nevertheless, Administrations which are studying Question\ 19/XII\ [1]
(recommended values of loudness ratings) may use this method for studies
relating to new types of telephone sets which do not contain carbon
microphones
.FS
The method may also be used for determining receiving loudness ratings
whether or not the telephone set contains a carbon microphone.
.FE
.
.PP
Administrations are also encouraged to use the method in studying
Question\ 7/XII\ [2] for expressing
loudness loss
on a common scale in
quality evaluation experiments.
.PP
The Recommendation describes a calculation method which gives results in
good agreement with those from subjective tests by the CCITT
Laboratory
.FS
The calculation method described in the Recommendation is based on weighting
factors which have been determined for the 20\ ISO\(hypreferred
frequencies. General applicability of the method would be improved if smoothed
analytic expressions were also available for use with other sets of
frequencies.
.FE
(see Recommendation\ P.78) using local telephone systems
having noncarbon microphones. For such local telephone systems, the methods
given in Recommendation\ P.64 should be used to determine the values of
sending and receiving sensitivities.
.PP
When
local telephone systems
containing carbon microphones are to be considered, the results obtained
so far from tests in the CCITT
Laboratory suggest that the method given in the present Recommendation can
still be used provided a suitable method is used to obtain the sending
sensitivities. Various measuring methods are being considered for this
purpose and are listed in Annex\ B to Recommendation\ P.64. Extensive
tests by the
CCITT Laboratory
using the
\*Qupper\(hyenvelope\*U method
show that this method gives good results for some types of
carbon
microphone
. The matter is being studied under Question\ 8/XII\ [3] (Measuring the
efficiency of a microphone or a receiver).
.PP
The loudness ratings of analogue telephone sets are determined
objectively by special measuring instruments conforming to
Recommendations\ P.64 and P.65 as regards the physical implementation, and to
the present Recommendations as regards the computational algorithm. However,
the results should not be applied directly for transmission planning, before
certain precautions have been observed regarding bandwidth and terminating
impedances.
.RT
.sp 2P
.LP
\fB1\fR     \fBIntroduction\fR
.sp 1P
.RT
.PP
Loudness ratings
according to the principles described in Recommendation\ P.76 can be determined
without recourse to subjective tests
provided that all the following conditions are fulfilled:
.RT
.LP
    a)
    a theoretical model is available having suitable structure;
.LP
    b)
    the appropriate values of the essential parameters of the
model are known;
.LP
    c)
     the sending and receiving sensitivities of the intermediate reference
systems are known;
.LP
    d)
    the sending and receiving sensitivities of the \*Qunknown\*U
local telephone systems and the insertion loss of the
intervening chain of circuits are known.
.PP
The methods of determining sending and receiving sensitivities
using
an artificial mouth and artificial ear are defined in Recommendation\ P.64.
The characteristics of the intermediate reference system determined according
to
the same methods are given in Recommendation\ P.48. The receiving sensitivities
obtained using the artificial ear now mentioned in Recommendation\ P.64
are not directly suitable for use in calculating loudness ratings but must
be corrected to allow for differences between sound pressures in real ears
under conditions of telephone conversations and those measured by the artificial
ear.
Information concerning this correction (\fIL\fR\d\fIE\fR\u) is given in
\(sc\ 6.
.bp
.sp 2P
.LP
\fB2\fR \fBDefinitions and symbols concerning sound pressures, sensitivities\fR
\fBand transmission losses\fR
.sp 1P
.RT
.PP
Definitions and symbols used in the subsequent description of
theoretical principles are listed below. Figure\ 1/P.79 illustrates
these.
.RT
.LP
.rs
.sp 23P
.ad r
\fBFigure 1/P.79, p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
2.1
    \fIConcerning talking\fR
.sp 9p
.RT
.PP
These definitions and symbols characterize the situation where a
subject is talking and they include his physical relationship to the telephone
or reference connection.
.RT
.LP
    MRP
    Point defining the
mouth reference point
; MRP is   at a defined location relative to the talker's lips. (See
Recommendation\ P.64.)
.LP
    \fIp\fR\d\fIM\fR\u    Sound pressure at MRP
.FS
The reference level or datum must be specified, e.g.\ 1 Pa, 20\ \(*mPa,\ etc.
.FE
in absence of any obstruction.
.LP
    \fIB\fR `
\fI\fI\d\fIS\fR\u    Spectrum density (long\(hyterm mean
pressure)
.FS
In practice, measurements are made in terms of sound pressure,
and that convention is retained for convenience of explanation. It is worth
noting that sound pressure relative to 20\ \(*mPa in a bandwidth of 1\ Hz is
approximately equal to sound intensity relative to 1\ pW/m\u2\d per Hz.
.FE
of speech referred to a MRP in dB relative to 20\ \(*mPa in a bandwidth of
1\ Hz.
.LP
    VL
    Vocal level, i.e. speech sound pressure (long\(hyterm rms
while talker is active) level of talker at the MRP; usually referred
to a reference vocal level as datum.
.LP
    SP
    Speaking position, i.e. the relative location of the
microphone of the telephone or reference system and the lips of the
talker.
.LP
.sp 1
.bp
.sp 1P
.LP
2.2
    \fIConcerning listening\fR
.sp 9p
.RT
.PP
These definitions and symbols characterize the situation where a
subject is listening and they include his physical relationship to the
telephone or reference connection:
.RT
.LP
    ERP
    Point defining the
ear reference point
(see
Recommendation\ P.64).
.LP
    \fIp\fR\d\fIE\fR\u    Sound pressure at ERP.
.LP
    \(*b\d0\u    Hearing threshold
for pure tones referred to an  ERP in dB relative to 20\ \(*mPa.
.LP
    \fIK\fR     A number, related to
Fletcher's critical frequency
bands
, required to convert hearing threshold for pure tones
to that for continuous\(hyspectrum sounds like speech.
.LP
     \(*b\d0\u\ \(em\ \fIK\fR Hearing threshold for continuous\(hyspectrum
sounds referred to an ERP in dB relative to 20\ \(*mPa in a bandwidth
of 1\ Hz.
.LP
    HL
    Hearing loss, usually referred to \*Qnormal\*U hearing
threshold.
.LP
    LC
     Listening conditions; the manner in which the earphone and its coupling
to the ear is related to the ERP.
.sp 1P
.LP
2.3
    \fIConcerning telephone or reference connections\fR
.sp 9p
.RT
.PP
These definitions and symbols serve to characterize the telephone or reference
connections in objective terms:
.RT
.LP
     \fIL\fR\d\fIM\fR\\d\fIE\fR\u Air\(hyto\(hyair transmission loss, in dB,
from a MRP to an ERP.
.LP
    JS,\ JR
     Electrical interfaces at the output of a sending local telephone system
and the input to a receiving local telephone system.
.LP
    LTC
    Local telephone system.
.LP
    \fIS\fR\d\fIM\fR\\d\fIJ\fR\u    Sending sensitivity of a local telephone system
from the MRP to the electrical output (JS).
.LP
     \fINote\fR \ \(em\ \fIS\fR\d\fIM\fR\\d\fIJ\fR\urelates to a median real
mouth; for practical purposes, sensitivities measured according to Recommendation\
P.64
using the recommended artificial mouth may be used for handset
telephones.
.LP
     \fIS\fR\d\fIJ\fR\\d\fIE\fR\u Receiving sensitivity of a local telephone
system from the electrical input (JR) to the ERP.
.LP
     \fINote\fR \ \(em\ \fIS\fR\d\fIJ\fR\\d\fIE\fR\urelates to a median real
ear; sensitivities measured with the artificial ear referred to in Recommendation\
P.64 and
according to the method described therein are denoted by the
symbol\ \fIS\fR\d\fIJ\fR\\d\fIe\fR\u. Such values must be corrected to give
appropriate values for \fIS\fR\d\fIJ\fR\\d\fIE\fR\u(see \(sc\ 6).
.LP
     \fIx\fR\d\fIJ\fR\\d\fIJ\fR\u Transmission loss between local telephone
systems, i.e. between JS and JR in Figure\ 1/P.79. The circuits concerned
in real
telephone connections will consist of trunk junctions, trunk circuits,
switching centres,\ etc. For assessment purposes this chain of
lines is replaced by nonreactive attenuators and filters,\ etc.
and referred to collectively by the word \*Qjunction\*U.
.LP
    \fIS\fR \s6\fIRMJ\fR .PS 10
,
\fIS\fR \s6\fIRJE\fR .PS 10
,
.RT
.LP
\fIL\fR \s6\fIRME\fR .PS 10
,\ etc.
.RT
.LP
\-v'1P'
\-v'8p'
     Values of \fIS\fR\d\fIM\fR\\d\fIJ\fR\u, \fIS\fR\d\fIJ\fR\\d\fIE\fR\u,
\fIL\fR\d\fIM\fR\\d\fIE\fR\u, etc., applicable to a reference speech path,\
e.g. NOSFER or the IRS defined in Recommendation\ P.48.
.LP
    \fIS\fR \s6\fIUMJ\fR .PS 10
,
\fIS\fR \s6\fIUJE\fR .PS 10
,
.RT
.LP
\fIL\fR \s6\fIUME\fR .PS 10
, etc.
.RT
.LP
\-v'1P'
\-v'8p'
     Values of \fIS\fR\d\fIM\fR\\d\fIJ\fR\u, \fIS\fR\d\fIJ\fR\\d\fIE\fR\u,
\fIL\fR\d\fIM\fR\\d\fIE\fR\u, etc., applicable to an unknown speech path,\
e.g. a telephone connection.
.LP
     \fIx\fR\d\fIU\fR\\d\fIR\fR\u, \fIx\fR\d\fIR\fR\\d\fIU\fR\u Values of
\fIx\fR applicable to combinations of \*Qunknown\*U sending to reference
receiving and reference sending to
\*Qunknown\*U receiving speech paths.
.LP
    \fIS\fR\d\fIM\fR\u    Sensitivity of a telephone microphone referred to a MRP.
.LP
    \fIS\fR\d\fIE\fR\u    Sensitivity of a telephone receiver referred to an ERP.
.LP
     \fIL\fR\d\fIS\fR\u Electrical transmission loss from the terminals of
a microphone to the line terminals of a telephone set.
.LP
    \fIL\fR\d\fIR\fR\u    Electrical transmission loss from the line terminals of a
telephone set to the terminals of a receiver.
.LP
    \fIL\fR \s6\fIINS\fR .PS 10
\ (\fISL\fR \ +\ \fIFB\fR )
    Transmission loss of
the combination of subscriber's line and feeding bridge.
.bp
.RT
.sp 2P
.LP
\fB3\fR     \fBStructure of the theoretical model\fR
.sp 1P
.RT
.sp 1P
.LP
3.1
    \fIDefinitions concerning loudness, its relationship to sensation\fR
\fIlevel and loudness ratings\fR
.sp 9p
.RT
.PP
These definitions and symbols relate to factors concerning loudness and
loudness ratings of telephone speech paths:
.RT
.LP
    \fIZ\fR     Sensation level
, in dB, of the received speech signal at a given frequency; describes
the portion of the received speech
signal which is above threshold and is, therefore, effective in
producing the
sensation of loudness
.
.LP
     \fIZ\fR\d\fIR\fR\\d\fIO\fR\u Value of \fIZ\fR when \fIL\fR\d\fIM\fR\\d\fIE\fR\u\
=\ 0 dB.
.LP
    \fIQ\fR (\fIZ\fR )
    Function of \fIZ\fR related to loudness; transforms
sensation level expressed in terms of\ \fIZ\fR , to loudness numerics.
.LP
    \fIm\fR     A parameter which can be used to define \fIQ\fR (\fIZ\fR );
represents the slope of 10\ log\d1\\d0\u\fIQ\fR (\fIZ\fR ) as function
of\ \fIZ\fR .
.LP
     \fIS\fR A monotonic function of frequency such that equal increments
of \fIS\fR are of equal importance to loudness, provided the associated
values of
\fIZ\fR are the same.
.LP
    \fIS\fR `
    The derivative of \fIS\fR with respect to frequency;
\fIS\fR `\ =\ d\fIS\fR /d\fIf\fR . \fIS\fR ` can be considered as a frequency
weighting factor.
.LP
    d\fIS\fR     From the foregoing, d\fIS\fR \ =\ \fIS\fR ` d\fIf\fR .
.LP
    \fIQ\fR (\fIZ\fR ) |
    Weighted average of
\fIQ\fR (\fIZ\fR ) which is related to the total loudness in a received
speech signal.
.LP
    \(*l
    Loudness of the sound being considered.
.LP
    OLR,\ SLR,
.LP
RLR,\ JLR
.LP
\-v'1P'
\-v'8p'
    Overall, sending and receiving and junction loudness ratings.
.sp 1P
.LP
3.2
    \fILoudness model\fR
.sp 9p
.RT
.PP
In considering speech transmission paths, it is necessary to define acoustical
terminals of the paths. This can be done in terms of MRP and ERP.
There are no unique definitions of such reference points, but those used
here are defined in Recommendation\ P.64.
.PP
Curve 1 in Figure\ 2/P.79 shows the spectrum density
\fIB\fR `
\fI\fI\d\fIS\fR\uof speech emitted at a certain vocal level and measured
at the MRP in the absence of any obstruction in front of the mouth
.FS
See
Annex\ A to Recommendation\ P.64 for the definition of MRP.
.FE
. The
measurement may be thought of as made with the aid of a very small measuring
microphone. When the speech reaches the ear of the other participant in a
telephone conversation, it will have been subjected to transmission loss and
distortion in the telephone speech path and the spectrum density may then
be as shown in Curve\ 2; the ERP to which Curve\ 2 is referred can, for
explanation, be thought of as located at the opening of the ear canal,
but might equally well be the tympanum, i.e.\ eardrum of the listener's
ear. The studies at present in hand make use of an ear reference point
located at the opening of the air canal (as referred to in Annex\ A to
Recommendation\ P.64). The interval \fIL\fR\d\fIM\fR\\d\fIE\fR\ubetween
curves\ 1 and\ 2 represents the \*Qmouth\(hyto\(hyear\*U transmission loss
and is, in general, frequency\(hydependent.
.PP
The received spectrum represented by Curve 2 does not contribute
uniformly to loudness, i.e.\ those portions of the spectrum lower in level
than the listener's threshold of hearing contributes very little compared
with those well above the threshold. Account is taken of this by defining
a quantity
termed \*Qsensation level\*U (symbol\ \fIZ\fR ) which is the interval between
the received spectrum, Curve\ 2, and the threshold of audibility for continuous
spectrum sounds (\(*b\d0\u\ \(em\ \fIK\fR ) shown in Curve\ 3. Loudness of the
received speech sound thus depends upon\ \fIZ\fR , which is, in general,
frequency\(hydependent.
.RT
.LP
.sp 1
.bp
.LP
.rs
.sp 32P
.ad r
\fBFigure 2/P.79, p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
Studies have shown
.FS
This model does not claim to represent
accurately all the features that relate to perception of the loudness of
speech; for example, the effects of interfrequency masking are ignored
and it does not predict the increasing importance of the lower frequencies
as the
intensity of the sound is increased from the threshold. It is possible to
construct models that represent more of the features fairly well, but no
completely comprehensive model is known. Such models are unnecessarily
complicated for calculating loudness ratings. The most important restriction
with respect to this model is that it should be used to make
comparisons at the constant listening level indicated in
Recommendation\ P.76.
.FE
that the loudness, \(*l, can be expressed
approximately as a function of \fIZ\fR in the following manner:
\v'6p'
.ce 1000
\(*l = C
@ pile { fIf\fR~\d2\u above int above \fIf\fR~\d1\u } @  \fIQ\fR \fI(Z)\fR \fIS\fR ` d
\fIf\fR
.ce 0
.ad r
(3\(hy1)
\v'1P'
\v'2p'
.ad b
.RT
.LP
.sp 1
.LP
where C is a constant, \fIQ\fR (\fIZ\fR ) is a \*Q
loudness growth
function
\*U which transforms\ \fIZ\fR so that equal increments of the transformed
values represent equal increments in loudness, \fIS\fR ` is a \*Q
frequency   weighting function
\*U which weights the transformed values of\ \fIZ\fR according to their
positions along the frequency scale and\ \fIf\fR\d1\uand\ \fIf\fR\d2\ucorrespond
to the lower and upper frequency limits for the band of
interest.
.bp
.PP
If desired the frequency scale can be transformed to a scale of
\fIS\fR , equal increments of which have the same \*Qimportance\*U so far
as loudness is concerned.
.PP
Thus:
\v'6p'
.RT
.ce 1000
\fIS\fR ` =
@ { ~\fIS\fR } over { ~\fIf\fR } @
.ce 0
.ad r
(3\(hy2)
\v'7p'
.ad b
.RT
.LP
.sp 1
.LP
which gives
\v'6p'
.ce 1000
\(*l = C
@ pile { fIS\fR~\d2\u above int above \fIS\fR~\d1\u } @  \fIQ\fR \fI(Z)\fR d
\fIS\fR
.ce 0
.ad r
(3\(hy3)
\v'1P'
\v'2p'
.ad b
.RT
.LP
.sp 1
where \fIS\fR\d1\uand \fIS\fR\d2\u | are points on the scale of \fIS\fR
 | that correspond
respectively to \fIf\fR\d1\uand \fIf\fR\d2\u.
.PP
The basic elements of the loudness rating process are shown in the flow
diagram of Figure\ 3/P.79. The flow diagram depicts a \*Qreference\*U spectrum
decreased by the loss of a telephone connection resulting in a received
spectrum which together with the threshold of hearing produces\ \fIZ\fR
, the values of which (as a function of frequency) are effective in producing
the sensation of loudness. Thus:
\v'6p'
.ce 1000
\fIZ\fR = \fIB\fR `\fI
\dS\u\fR \(em \fIL
\dME
\u\fR \(em (\(*b
\d0\u \(em \fIK\fR )
.ce 0
.ad r
(3\(hy4)
.ad b
.RT
.LP
.sp 1
.LP
and \fIZ\fR  | as a function of frequency is converted to loudness, \(*l,
according to the equations explained above in which \fIZ\fR is transformed
to loudness numerics which are then weighted by the frequency weighting
function to produce
\fIQ\fR (\fIZ\fR ) |
; a constant applied to
\fIQ\fR (\fIZ\fR ) |
produces
\(*l, the loudness of the received speech expressed on some suitable scale.
.LP
.rs
.sp 11P
.ad r
\fBFigure 3/P.79, p. \fR
.sp 1P
.RT
.ad b
.RT
.LP
\fR
.PP
The flow diagram of Figure 3/P.79\fR represents only basic elements in
the loudness rating process. These elements require further specification
in order to render them unique. For example, \fIB\fR `
\fI\fI\d\fIS\fR\udepends on the particular speaker and his vocal level,
the test phrase used, and the location of the talker's lips with respect
to the telephone microphone defined by his
individual method of usage and by the somewhat arbitrarily defined MRP.
Similarly, the received spectrum level depends on the particular listener
and his characteristics, e.g.\ fit between his ear and the telephone earphone
when the handset is held in a prescribed manner, whether or not he has
a hearing
loss, and on the ERP.
.PP
Furthermore, transmission planning studies require subdivision of the connection
loss, \fIL\fR\d\fIM\fR\\d\fIE\fR\u, into component parts, e.g.\ a sending
component, a receiving component and an interconnecting component.
.PP
The function \fIQ\fR (\fIZ\fR ) can, in part, be specified in terms of
a parameter\ \fIm\fR which is the slope of the logarithm of \fIQ\fR (\fIZ\fR
) when plotted against\ \fIZ\fR . \fIm\fR does, however, depend upon the
listening level
(or \fIZ\fR ) in the general case but may be considered constant over a
wide and useful range of\ \fIZ\fR .
.bp
.PP
Those additional factors considered at present to be of importance are
included in the more detailed flow diagram of Figure\ 4/P.79 which is an
expansion of Figure\ 3/P.79. The influence of these factors can be appreciated
from the previous discussion and from review of the definitions given in
\(sc\ 3.1. Figure 3/P.79 supplements these definitions.
.RT
.LP
.rs
.sp 31P
.ad r
\fBFigure 4/P.79, p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
\fB4\fR     \fBValues of the parameters\fR
.sp 1P
.RT
.sp 1P
.LP
4.1
    \fIGeneral\fR
.sp 9p
.RT
.PP
To implement the model in the form described in \(sc\ 3, it is,
in principle, necessary to assign values to the following parameters:
.PP
\fIB\fR `
\fI\fI\d\fIS\fR\u | as a function of frequency
.PP
10 log\d1\\d0\u\fIS\fR ` as a function of frequency
.PP
\fIm\fR  | which (partly) defines the
loudness growth function
\fIQ\fR (\fIZ\fR )
.PP
\(*b\d0\u\ \(em\ K as a function of frequency.
.PP
In fact, for the present purposes, it is convenient to group all these
parameters together into a single frequency\(hydependent parameter which
can be
used with \fIm\fR for the purposes of calculating sending, receiving and
junction loudness ratings and the loudness insertion loss of electrical
elements such as channel filters in commercial telephone connections.
.PP
The theoretical derivation of this frequency\(hydependent parameter \fIG\fR
, is explained below.
.PP
\fIG\fR , together with \fIm\fR , can be estimated directly from the
results of subjective loudness balance tests conducted using sets of lowpass
and highpass filters in a suitable reference system.
.bp
.RT
.sp 1P
.LP
4.2
    \fITheoretical derivation of G\fR
.sp 9p
.RT
.PP
Equation 3\(hy1 can be written:
\v'6p'
.RT
.ce 1000
\(*l\fI
\dU\u\fR = C
@  int  @ \fIQ\fR (\fIZ
\dU\u\fR ) \fIS\fR ` d
\fIf\fR
.ce 0
.ad r
(4\(hy1a)
\v'1P'
\v'2p'
.ad b
.RT
.LP
and
\v'6p'
.ce 1000
\(*l\fI
\dR\u\fR = C
@  int  @ \fIQ\fR (\fIZ
\dR\u\fR ) \fIS\fR ` d
\fIf\fR
.ce 0
.ad r
(4\(hy1b)
\v'1P'
\v'2p'
.ad b
.RT
.LP
.sp 1
where \(*l\fI\fI\d\fIU\fR\uand \(*l\fI\fI\d\fIR\fR\urepresent the loudness
of speech received through the \*Qunknown\*U and reference speech paths
respectively and \fIZ\fR\d\fIU\fR\uand \fIZ\fR\d\fIR\fR\u
are the corresponding values of sensation level (which are functions of
frequency).
.PP
The calculation method to be described depends upon the assumption (largely
verified for restricted ranges of listening level) that the
function\ \fIQ\fR (\fIZ\fR ) can be put in the form:
\v'6p'
.ce 1000
\fIQ\fR (\fIZ\fR ) = constante \(mu 10\fI
\um\fR (1/10)
\fIZ
\d\fR
.ce 0
.ad r
(4\(hy2)
.ad b
.RT
.LP
.sp 1
(The base 10 and the multiplier 1/10 are used merely to preserve the analogy
to the decibel, in which unit \fIZ\fR is expressed.)
.PP
Let
\v'6p'
.ce 1000
\fIZ
\dRO
\u\fR = \fIB\fR `\fI
\dS\u\fR \(em (\(*b
\d0\u \(em \fIK\fR )
.ce 0
.ad r
(4\(hy3)
.ad b
.RT
.LP
.sp 1
and substitute in Equation 3\(hy4 to obtain:
\v'6p'
.ce 1000
\fIZ
\dU\u\fR = \fIZ
\dRO
\u\fR \(em \fIL
\dUME
\u\fR
.ce 0
.ad r
(4\(hy4a)
.ad b
.RT
.ce 1000
\fIZ
\dR\u\fR = \fIZ
\dRO
\u\fR \(em \fIL
\dRME
\u\fR
.ce 0
.ad r
(4\(hy4b)
.ad b
.RT
.PP
.sp 1
By substituting Equations (4\(hy4a) and (4\(hy4b) in Equations (4\(hy1a)
and (4\(hy1b) and rearranging:
\v'6p'
.ce 1000
\(*l\fI
\dU\u\fR = C
@  int  @ 10
\u\(em\fIm\fR (1/10)
\fIL\fR \fIUME\fR
\d
[10\fI
\um\fR (1/10)
\fIZ\fR \fIRO\fR \fI
\d\fR \fIS\fR `
]
d
\fIf\fR
.ce 0
.ad r
(4\(hy5a)
\v'1P'
\v'2p'
.ad b
.RT
.ce 1000
.sp 1
\(*l\fI
\dR\u\fR = C
@  int  @ 10
\u\(em\fIm\fR (1/10)
\fIL\fR \fIRME\fR
\d
[10\fI
\um\fR (1/10)
\fIZ\fR \fIRO\fR \fI
\d\fR \fIS\fR `
]
d
\fIf\fR
.ce 0
.ad r
(4\(hy5b)
\v'1P'
\v'2p'
.ad b
.RT
.PP
.sp 1
The loudness rating can be considered to be the \(*D\fIx\fR
(independent of frequency) removed from the \*Qunknown\*U speech path to render
\(*l\fI\fI\d\fIU\fR\u\ =\ \(*l\fI\fI\d\fIR\fR\u.
.PP
Using the substitution:
\v'6p'
.RT
.ce 1000
\fIG\fR = [10\fI
\um\fR (1/10)
\fIZ\fR \fIRO\fR \fI
\d\fR \fIS\fR `
]
.ce 0
.ad r
(4\(hy6)
.ad b
.RT
.LP
.sp 1
and inserting \fIL\fR \s6\fIUME\fR .PS 10
\ \(em\ \(*D\fIx\fR in Equation (4\(hy5a) in place of \fIL\fR \s6\fIUME\fR
.PS 10
, we obtain equality of the \(*l's.
.bp
.RT
.PP
Therefore
\v'6p'
.ce 1000
@  int  @ 10
\u\(em\fIm\fR (1/10)
(\fIL\fR \fIUME\fR
\(em\(*D
\fIx\fR )
\d \fIG\fR d
\fIf\fR
=
@  int  @ 10
\u\(em\fIm\fR (1/10)
\fIL\fR \fIRME\fR
\d \fIG\fR
d
\fIf\fR
.ce 0
.ad r
(4\(hy7)
\v'10p'
.ad b
.RT
.LP
.sp 1
.ce 1000
10
\u\(em\fIm\fR (1/10)\(*D
\fIx\fR \d =
@ {  int   | 0~\u\(em\fIm\fR (1/10) \fIL\fR~\fIUME\fR~\d~\fIG\fR~d~\fIf\fR } over {  int  | 0~\u\(em\fIm\fR (1/10) \fIL\fR~\fIRME\fR~\d~\fIG\fR~d~\fIf\fR } @
.ce 0
.ad r
(4\(hy8)
.ad b
.RT
.LP
and
.ce 1000
\(*D
\fIx\fR = \(em\fIm\fR \u\(em1
\d 10
log
\d10
\u |
@  int  @  | 0
\u\(em\fIm\fR (1/10)
\fIL\fR \fIUME\fR
\d \fIG\fR d
\fIf\fR \(em
@ left { \fR~\(em\fIm\fR~\u\(em1~\d~10~log~\d10~\u |  int  | 0~\u\(em\fIm\fR (1/10) \fIL\fR~\fIRME\fR~\d~\fIG\fR~d~\fIf\fR~ right } @
.ce 0
.ad r
(4\(hy9)
.ad b
.RT
.LP
.sp 1
.PP
Without affecting the equality, \fIG\fR can be scaled by multiplying with
a suitable constant to render \(is\fIG\fR \ d\fIf\fR \ =\ 1; \fIG\fR can
then be treated as a weighting factor
.FS
From Equations\ (4\(hy3) and\ (4\(hy6) it can be seen that \fIG\fR as  a
function of frequency depends upon the value of \fIm\fR and the frequency\(hydependent
functions\ \fIB\fR `
\fI\fI\d\fIS\fR\u, \(*b\d0\u, \fIK\fR and \fIS\fR '
.
.FE
and each term on the right\(hyhand side takes the form:
\v'6p'
.sp 1P
.ce 1000
\(*F
\u\(em1
\d
@ left [   int  (*F (\fIL\fR ) \fIG\fR~d~\fIf\fR right ] @  =
\fIL\fR  |
.ce 0
.sp 1P
.LP
.sp 1
Then for the loudness rating we have
\v'6p'
.ce 1000
loudness rating = \(*D
\fIx\fR =
\fIL
\dUME
\u\fR  |
\(em
\fIL
\dRME
\u\fR  |
.ce 0
.ad r
(4\(hy10)
.ad b
.RT
.LP
.sp 1
.PP
The terms
\fIL
\dUME
\u\fR  |
and
\fIL
\dRME
\u\fR  |
can be considered as
the \*Qweighted average mouth to ear loss\*U of the \*Qunknown\*U and reference
speech paths respectively. In each of the foregoing equations, integration
(and
therefore averaging) is over the range between lower and upper frequency
limits of interest.
.PP
For computation, the audible range of frequency is divided into a
number (\fIN\fR ) of continuous band; use is made here of the 20\ ISO\(hypreferred
bands centred at frequencies spaced at approximately 1/3 octaves from\
100
to\ 8000\ Hz. Averaging the values of
\fIL
\dUME
\u\fR  |
is then performed by
summations of the form:
\v'6p'
.RT
.ce 1000
\fIL
\dUME
\u\fR  |
= \(em\fIm\fR \u\(em1
\d 10
log
\d10
\u
@ pile { fIN\fR above sum above \fIi\fR } @10
\u\(em\fIm\fR (1/10)
\fIL\fR \fIUME\fR
\d \fIG\fR \(*D
\fIf\fR
.ce 0
.ad r
(4\(hy11)
\v'8p'
.ad b
.RT
.LP
.sp 1
.PP
The
acoustical transmission loss of a speech path
is, in   general, a function of frequency and can be defined as:
\v'6p'
.ce 1000
\fIL
\dUME
\u\fR  |  20
log
\d10
\u
@ { fIp~\dM\u\fR } over { fIp~\dE\u\fR } @
.ce 0
.ad r
(4\(hy12)
\v'7p'
.ad b
.RT
.LP
.sp 1
where \fIp\fR\d\fIM\fR\u | and \fIp\fR\d\fIE\fR\u | are as defined in \(sc\(sc\
2.1 and 2.2.\fR
.PP
It is necessary to know the values of \fIL\fR \s6\fIUME\fR .PS 10
at each frequency together with \fIG\fR \(*D\fIf\fR ; naturally,
\fIL\fR \s6\fIUME\fR .PS 10
depends on the telephone speech path under
consideration but \fIG\fR \(*D\fIf\fR and other information common to all speech
paths is described below.
.RT
.sp 1P
.LP
4.3
    \fIDetermination of values for G\fR
.sp 9p
.RT
.PP
Values have been assigned to \fIG\fR by analysis of results of loudness
balance tests by the CCITT Laboratory using a special speech path consisting
of NOSFER, but with its sending frequency response made more level by
equalization. Each of a set of special low\(hy and high\(hypass filters
was inserted in turn in the \*Qjunction\*U of this speech path.
.bp
.PP
Balances were made with each filter and with the \*Qthrough\*U path; each
was treated as the \*Qunknown\*U while balancing for determining relative
equivalents against NOSFER with its junction set at 25\ dB. Balancing was
done by the \*Q
margin\*U method
, i.e.\ by changing the transmission loss in the \*Qunknown\*U. Values
of \(*D\fIx\fR were calculated for each filter and corrected for
the transmission loss in the pass\(hyband. The cut\(hyoff frequencies were
taken as those frequencies at which the transmission loss was 10\ dB greater
than the
pass\(hyband transmission loss.
.PP
By smoothing the results and interpolating at the appropriate
edges of the 20\ ISO\(hypreferred frequency bands centred at the frequencies
from 100\(hy8000\ Hz, it was possible, first, to estimate\ \fIm\fR ; \fIm\fR
\ =\ 3/\(*D\fIx\fR , if we take the value of \(*D\fIx\fR at the frequency
where \(*D\fIx\fR was the same for low\(hy and
for high\(hypass filtering. Then, by use of Equation\ (4\(hy8) and some
interaction, it
was possible to obtain a set of values for \fIG\fR which satisfied the
experimental data. Note that \fIL\fR \s6\fIRME\fR .PS 10
in Equations\ (4\(hy7) to (4\(hy10)
represents the mouth\(hyto\(hyear transmission loss of the \*Qthrough\*U
path and
\fIL\fR \s6\fIUME\fR .PS 10
represents that of the same path with the filter
inserted.
.RT
.PP
The results are given in Table 1/P.79, the value determined for
\fIm\fR  | being 0.175.
.RT
.ce
\fBH.T. [T1.79]\fR
.ce
TABLE\ 1/P.79
.ce
\fBValues of 10 log\fR\(da\fB1\fR\(da\fB0 \fR
.ce
\fIG\fR
.ce
\fBand 10 log\fR\(da\fB1\fR\(da\fB0\fR
.ce
\fIG\fR
.ce
\(*D\fIf\fR
.ce
\fBdetermined by the CCITT Laboratory\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
Midfrequency  (Hz)    \(*D\fIf\fR  (Hz)    10 log 1 0 \fIG\fR  (dB)     {
10 log
1
0 \fIG\fR
\(*D\fIf\fR
(dB)
 }
_
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
\ 100    \ \ 22.4    \(em32.63    \(em19.12
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
\ 125    \ \ 29.6    \(em29.12    \(em14.41
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
\ 160    \ \ 37.5    \(em27.64    \(em11.90
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
\ 200    \ \ 44.7    \(em28.46    \(em11.96
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
\ 250    \ \ 57.0    \(em28.58    \(em11.02
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
\ 315    \ \ 74.3    \(em31.10    \(em12.39
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
\ 400    \ \ 92.2    \(em29.78    \(em10.14
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
\ 500    \ 114.0    \(em32.68    \(em12.12
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
\ 630    \ 149.0    \(em33.21    \(em11.48
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
\ 800    \ 184.0    \(em34.14    \(em11.49
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
1000    \ 224.0    \(em35.33    \(em11.83
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
1250    \ 296.0    \(em37.90    \(em13.19
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
1600    \ 375.0    \(em38.41    \(em12.67
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
2000    \ 447.0    \(em41.25    \(em14.75
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
2500    \ 570.0    \(em41.71    \(em14.15
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
3150    \ 743.0    \(em45.80    \(em17.09
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
4000    \ 922.0    \(em43.50    \(em13.86
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
5000    1140.0    \(em47.13    \(em16.56
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
6300    1490.0    \(em48.27    \(em16.54
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
8000    1840.0    \(em46.47    \(em13.82
_
.TE
.nr PS 9
.RT
.ad r
\fBTable 1/P.79 [T1.79], p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
\fB5\fR     \fBCalculation of loudness ratings\fR
.sp 1P
.RT
.sp 1P
.LP
5.1
    \fIDeviation of formulas and W weights\fR
.sp 9p
.RT
.PP
The method described in Recommendation P.78 can be described in
terms of the flow diagrams illustrated in Figure\ 5/P.79 which also embody
the structure of the model used here (Figure\ 4/P.79). The diagrams placed
on the
left in parts a), b), c) and d) of Figure 5/P.79 are redrawn versions of the
various paths given in Figure\ 1/P.78.
.PP
Figure 5/P.79 illustrates the procedure when values are known for
all the parameters referred to in \(sc\(sc\ 1, 2 and\ 3. In a) of Figure
5/P.79, the
parameters shown grouped together are those used to form the composite
parameter\ \fIG\fR described in \(sc\ 4. Further grouping is possible as
shown in b), c) and\ d) of Figure 5/P.79. It will also be seen that the
whole of the path from \fIx\fR\d\fIR\fR\uto \(*l\fI\fI\d\fIR\fR\uis also
common to all four flow diagrams. Use can be made of this feature to reduce
the calculation procedure to a formula which is very
easy to compute.
.bp
.RT
.LP
.rs
.sp 47P
.ad r
\fBFigure 5/P.79 + Remarques, p. 27\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 24P
.ad r
\fBFigure 5/P.79 (suite), p. 28\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 24P
.ad r
\fBFigure 5/P.79 (suite), p. 29\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 24P
.ad r
\fBFigure 5/P.79 (fin), p. 30\fR
.sp 1P
.RT
.ad b
.RT
.PP
Taking \fIm\fR  | s constant with the value 0.175, use can be made of the
substitution:
\v'6p'
.ce 1000
\fIW
\di\u\fR = \(em57.1 log
\d10
\u \fIG\fR \(*D
\fIf\fR
.ce 0
.ad r
(4\(hy13)
.ad b
.RT
.PP
.sp 1
Equation (4\(hy11) can then be simplified in appearance to:
\v'6p'
.ce 1000
\fIL
\dUME
\u\fR  |
= \(em57.1
log
\d10
\u
@ pile { fIN\fR above sum above \fIi\fR } @10
\u\(em(1/57.1) (
\fIL\fR \fIUME\fR +
\fIW\fR \fIi\fR
)
\d
.ce 0
.ad r
\ \ (4\(hy14)
\v'8p'
.ad b
.RT
.LP
.sp 1
.PP
For the present purposes, the reference speech path will be taken as the
\*Qintermediate reference system\*U (IRS) defined in
Recommendation\ P.48
and set with its attenuator at 0\ dB; having fixed the reference speech path,
\fIL\fR\d\fIR\fR\\d\fIM\fR\\d\fIE\fR\ubecomes constant, i.e.\ independent
of\ \fIi\fR .
Therefore Equations\ (4\(hy10) and\ (4\(hy14) can be combined to form:
\v'6p'
.ce 1000
loudness rating = \(em57.1 log
\d10
\u
@ pile { fIN\fR above sum above \fIi\fR } @10
\u\(em(1/57.1)
(
\fIL\fR \fIUME\fR \(em
\fIL\fR \fIRME\fR  |
+
\fIW\fR \fIi\fR
)
\d
.ce 0
.ad r
(4\(hy15)
\v'8p'
.ad b
.RT
.LP
.sp 1
.PP
When rating commercial local telephone circuits, the values of
\fIL\fR\d\fIU\fR\\d\fIM\fR\\d\fIE\fR\u | an be obtained for any given \*Qunknown\*U
speech path combining appropriate sending and receiving sensitivites, \fIS\fR\d\fIM\fR\\d\fIJ\fR\uand
\fIS\fR\d\fIJ\fR\\d\fIE\fR\u, in appropriate combinations.
.PP
For determining an \*Q
overall loudness rating
\*U
(OLR),
\v'6p'
.RT
.ce 1000
\fIL
\dUME
\u\fR = \(em(\fIS
\dUMJ
\u\fR + \fIS
\dUJE
\u\fR )
.ce 0
.ad r
(4\(hy16a)
.ad b
.RT
.LP
.sp 1
.bp
.PP
For determining a
sending loudness rating
(SLR) of a
local telephone circuit,
\v'6p'
.ce 1000
\fIL
\dURME
\u\fR = \(em(\fIS
\dUMJ
\u\fR + \fIS
\dRJE
\u\fR )
.ce 0
.ad r
(4\(hy16b)
.ad b
.RT
.LP
.sp 1
.PP
For determining a
receiving loudness rating
(RLR) of a
local telephone circuit,
\v'6p'
.ce 1000
\fIL
\dRUME
\u\fR = \(em(\fIS
\dRMJ
\u\fR + \fIS
\dUJE
\u\fR )
.ce 0
.ad r
(4\(hy16c)
.ad b
.RT
.LP
.sp 1
and for determining a \*Q
junction\*U loudness rating
(JLR)
\v'6p'
.LP
\fIL
\dUJME
\u\fR = \(em(\fIS
\dRMJ
\u\fR + \fIS
\dRJE
\u\fR ) +
\fIx
\dJJ
\u\fR
.LP
and
(4\(hy16d)
\fIL
\dRMEO
\u\fR = \(em(\fIS
\dRMJ
\u\fR + \fIS
\dRJE
\u\fR )
.LP
.sp 1
.PP
Substituting these in Equation (4\(hy15):
\v'6p'
.ce 1000
OLR = \(em57.1 log
\d10
\u
@ pile { fIN\fR above sum above \fIi\fR } @10
\u(1/57.1)
(
\fIS\fR \fIUMJ\fR + \fIS\fR \fIUJE\fR +
\fIL\fR \fIRME\fR  |
\(em \fIW\fR \fIi\fR
)
\d
.ce 0
.ad r
(4\(hy17a)
\v'8p'
.ad b
.RT
.ce 1000
.sp 1
SLR = \(em57.1 log
\d10
\u
@ pile { fIN\fR above sum above \fIi\fR } @10
\u(1/57.1)
(
\fIS\fR \fIUMJ\fR + \fIS\fR \fIRJE\fR +
\fIL\fR \fIRME\fR  |
\(em \fIW\fR \fIi\fR
)
\d
.ce 0
.ad r
(4\(hy17b)
\v'8p'
.ad b
.RT
.ce 1000
.sp 1
RLR = \(em57.1 log
\d10
\u
@ pile { fIN\fR above sum above \fIi\fR } @10
\u(1/57.1)
(
\fIS\fR \fIUJE\fR + \fIS\fR \fIRMJ\fR +
\fIL\fR \fIRME\fR  |
\(em \fIW\fR \fIi\fR
)
\d
.ce 0
.ad r
(4\(hy17c)
\v'8p'
.ad b
.RT
.LP
.sp 1
.ce 1000
JLR = \(em57.1 log
\d10
\u
@ pile { fIN\fR above sum above \fIi\fR } @10
\u(1/57.1)
(\(em\fIx\fR \fIJJ\fR \(em \fIL\fR \fIRMEO\fR +
\fIL\fR \fIRME\fR  |
\(em  \fIW\fR \fIi\fR
)
\d
.ce 0
.ad r
(4\(hy18)
\v'8p'
.ad b
.RT
.PP
.sp 1
The terms
\fIL
\dRME
\u\fR  |
and \fIW\fR\d\fIi\fR\u | are common to each of the
Equations\ (4\(hy17) and so further computational simplification is possible by
making the following substitutions:
\v'6p'
.ce 1000
\fIW
\dO\u\fR = \fIW
\di\u\fR \(em
\fIL
\dRME
\u\fR  |
.ce 0
.ad r
(4\(hy18a)
.ad b
.RT
.ce 1000
.sp 1
\fIW
\dS\u\fR = \fIW
\di\u\fR \(em \fIS
\dRJE
\u\fR \(em
\fIL
\dRME
\u\fR  |
.ce 0
.ad r
(4\(hy18b)
.ad b
.RT
.LP
.sp 1
.ce 1000
\fIW
\dR\u\fR = \fIW
\di\u\fR \(em \fIS
\dRMJ
\u\fR \(em
\fIL
\dRME
\u\fR  |
.ce 0
.ad r
(4\(hy18c)
.ad b
.RT
.ce 1000
.sp 1
\fIW
\dJ\u\fR = \fIW
\di\u\fR + \fIL
\dRMEO
\u\fR \(em
\fIL
\dRME
\u\fR  |
.ce 0
.ad r
(4\(hy18d)
.ad b
.RT
.PP
.sp 1
When the substitutions are made, the equations become:
\v'6p'
.ce 1000
OLR = \(em57.1 log
\d10
\u
@ pile { fIN\fR above sum above \fIi\fR } @10
\u(1/57.1)
(
\fIS\fR \fIUMJ\fR + \fIS\fR \fIUJE\fR \(em \fIW\fR \fIO\fR
)
\d
.ce 0
.ad r
(4\(hy19a)
\v'8p'
.ad b
.RT
.ce 1000
.sp 1
SLR = \(em57.1 log
\d10
\u
@ pile { fIN\fR above sum above \fIi\fR } @10
\u(1/57.1)
(
\fIS\fR \fIUMJ\fR \(em \fIW\fR \fIS\fR
)
\d
.ce 0
.ad r
(4\(hy19b)
\v'8p'
.ad b
.RT
.LP
.sp 1
.ce 1000
RLR = \(em57.1 log
\d10
\u
@ pile { fIN\fR above sum above \fIi\fR } @10
\u(1/57.1)
(
\fIS\fR \fIUJE\fR \(em \fIW\fR \fIR\fR
)
\d
.ce 0
.ad r
(4\(hy19c)
\v'8p'
.ad b
.RT
.ce 1000
.sp 1
JLR = \(em57.1 log
\d10
\u
@ pile { fIN\fR above sum above \fIi\fR } @10
\u(1/57.1)
(
\(em\fIx\fR \fIJJ\fR \(em \fIW\fR \fIJ\fR
)
\d
.ce 0
.ad r
(4\(hy19d)
\v'8p'
.ad b
.RT
.LP
.sp 1
.bp
.PP
Table 2/P.79 shows the values for these \*Qweighting\*U factors which have
been derived from the information in Table\ 1/P.79 with \fIm\fR \ =\ 0.175.
.LP
.sp 4
.ce
\fBH.T. [T2.79]\fR
.ce
TABLE\ 2/P.79
.ce
\fBWeighting factors for calculating loudness ratings\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
Band  No.    Mid\(hy frequency  (Hz)    Send  \fIW\fI      Receive  \fIW\fI      Junction  \fIW\fI      Overall \fIW\fI
_
.T&
cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
\ 1    \ 100    154.5    152.8    200.3    107.0
.T&
cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
\ 2    \ 125    115.4    116.2    151.5    \ 80.1
.T&
cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
\ 3    \ 160    \ 89.0    \ 91.3    114.6    \ 65.7
.T&
cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
\ 4    \ 200    \ 77.2    \ 85.3    \ 96.4    \ 66.1
.T&
cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
\ 5    \ 250    \ 62.9    \ 75.0    \ 77.2    \ 60.7
.T&
cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
\ 6    \ 315    \ 62.3    \ 79.3    \ 73.1    \ 68.5
.T&
cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
\ 7    \ 400    \ 45.0    \ 64.0    \ 53.4    \ 55.6
.T&
cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
\ 8    \ 500    \ 53.4    \ 73.8    \ 60.3    \ 66.9
.T&
cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
\ 9    \ 630    \ 48.8    \ 69.4    \ 54.9    \ 63.3
.T&
cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
10    \ 800    \ 47.9    \ 68.3    \ 52.8    \ 63.4
.T&
cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
11    1000    \ 50.4    \ 69.0    \ 54.1    \ 65.3
.T&
cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
12    1250    \ 59.4    \ 75.4    \ 61.7    \ 73.1
.T&
cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
13    1600    \ 57.0    \ 70.7    \ 57.6    \ 70.1
.T&
cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
14    2000    \ 72.5    \ 81.7    \ 72.2    \ 82.0
.T&
cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
15    2500    \ 72.9    \ 76.8    \ 71.1    \ 78.6
.T&
cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
16    3150    \ 89.5    \ 93.6    \ 87.7    \ 95.4
.T&
cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
17    4000    117.3    114.1    154.5    \ 76.9
.T&
cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
18    5000    157.3    144.6    209.5    \ 92.4
.T&
cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
19    6300    172.2    165.8    245.8    \ 92.2
.T&
cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
20    8000    181.7    166.7    271.7    \ 76.7
_
.TE
.nr PS 9
.RT
.ad r
\fBTableau 2/P.79 [T2.79], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 4
.sp 1P
.LP
5.2
    \fILoudness rating calculations over a reduced bandwidth\fR
.sp 9p
.RT
.PP
In practical cases the complete information for all 20\ bands may
not be available, or, for some extreme bands, may not be reliable. In such
cases it will be desirable to restrict the frequency range over which
calculations of loudness are made.
.PP
This may be done quite simply by using only those bands for which
reliable figures exist and making an allowance equal to the loudness rating
of the overall IRS connection calculated over the same reduced bandwidth.
This
allowance may conveniently be incorporated into the calculations by reducing
the
\fIW\fR weights
uniformly by an appropriate figure, or by simply
reducing (subtracting from) the resulting loudness rating by the
allowance.
.PP
Table 3/P.79 gives some examples of the allowance to be applied for
various reduced bandwidths.
.PP
Other allowances may be calculated by determining the
IRS overall  loudness rating
for the required bandwidth.
.bp
.RT
.ce
\fBH.T. [T3.79]\fR
.ce
TABLE\ 3/P.79
.ce
\fBAllowance to be subtracted\fR
.ce
\fBfrom\fR
.ce
\fIW\fR
.ce
\fBweights for reduced bandwidths\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(72p) | cw(48p) .
Bands    Allowance
_
.T&
cw(72p) | cw(48p) .
3 \(em 18 (inclusive)    0.1 dB
.T&
cw(72p) | cw(48p) .
3 \(em 17 (inclusive)    0.1 dB
.T&
cw(72p) | cw(48p) .
4 \(em 18 (inclusive)    0.3 dB
.T&
cw(72p) | cw(48p) .
4 \(em 17 (inclusive)    0.3 dB
.T&
cw(72p) | cw(48p) .
6 \(em 16 (inclusive)     {
2.1 dB
\fINote\fR
\ \(em\ For loudness rating measuring instruments designed in accordance with the present Recommendation, the only bandwidth options recommended are:
.LP
\fBi\fR
i)\ 100\(hy8000 Hz, bands 1\(hy20 (inclusive)
ii)\ 200\(hy4000 Hz, bands 4\(hy17 (inclusive)
.nr PS 9
.RT
.ad r
\fBTable 3/P.79 [T3.79], p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
5.3
     \fISending loudness rating (SLR) and receiving loudness rating (RLR)\fR
\fIvalues to be used in the series G\ Recommendations\fR
.sp 9p
.RT
.PP
Commercial measuring instruments complying with the present
Recommendation use a band of 200\ to 4000\ Hz or even 100\ to 8000\ Hz. This is
much wider than the band for which CCITT Recommendations specify an assured
transmission (namely 300\ to 3400\ Hz). (See, for instance, Recommendations\
G.132 and\ G.151).
.PP
Thus, in a national system which may be included in an international connection,
the loudness of the analogue telephone set should be considered as the
inferior to the values measured herein.
.PP
It should also be noted that the loudness rating measurements of
Recommendations\ P.64 to\ P.79 are to be made with a terminating impedance of
600\ ohms. This is most often not the impedance appearing in the 2\(hywire
part of the network. For various reasons, many Administrations now specify
a complex
nominal impedance. Thus, there will be a mismatch effect.
.PP
For SLR and RLR, an investigation has been made for a range of
typical analogue telephone set sensitivity and impedance characteristics as
well as nominal impedances. The result is that, with sufficient practical
accuracy, 1\ dB should be added to the measured values of SLR and RLR of
\fIanalogue\fR telephone sets in the LR planning of networks which can
be included in an international connection. Thus, with the designation
of SLR\dw\u\fR and
RLR\dw\ufor the measure values:
\v'6p'
.RT
.sp 1P
.ce 1000
\fISLR\fR = \fISLR\fI\d\fIw\fR\u+ 1
.ce 0
.sp 1P
.ce 1000
\fIRLR\fR = \fIRLR\fI\d\fIw\fR\u+ 1
.ce 0
.sp 1P
.LP
.sp 1
.PP
The same correction, it should be noted, also applies when an
unloaded subscriber cable is included in the mesurements of this
Recommendation.
.PP
(When this correction is applied for planning, the effect of an
unloaded subscriber's line on the LR is equal to its insertion loss at about
1\ kHz. See also Annex\ A to Recommendation\ G.111.)
.PP
For digital sets, however, the correction is \fInot\fR  | needed because
the codec and filters in the set limit the band to a certain extent.
.PP
As a rule it can be understood, from the context, when SLR and RLR
values refer to planning or to measured (analogue) set values. However, when
confusion might arise, it should be clearly stated whether the values refer
to planning or measurements.
.bp
.RT
.sp 2P
.LP
\fB6\fR     \fBSensitivity and transmission loss data required\fR
.sp 1P
.RT
.PP
The
sending sensitivity of the local telephone system
,
\fIS\fR\d\fIM\fR\\d\fIJ\fR\u, should be determined in principle using real
mouths and real speech but it is usually sufficient to make these measurements
using an
artificial mouth and suitable test signal. See Recommendation\ P.64 for
particulars.
.PP
The
receiving sensitivity of the local telephone system
,
\fIS\fR\d\fIJ\fR\\d\fIE\fR\u, should be determined in principle using real
ears. The
determination of the sensitivity denoted by \fIS\fR\d\fIJ\fR\\d\fIe\fR\u,
using an
artificial ear, is explained in Recommendation\ P.64 but this quantity
differs from the quantity required here by the artificial/real ear correction
\fIL\fR\d\fIE\fR\u, that is:
\v'6p'
.RT
.sp 1P
.ce 1000
\fIS\fR\d\fIJ\fR\\d\fIE\fR\u\ =\ \fIS\fR\d\fIJ\fR\\d\fIe\fR\u\ \(em\ \fIL\fR\d\fIE\fR\u
.ce 0
.sp 1P
.LP
.sp 1
.PP
The value of \fIL\fR\d\fIE\fR\u | usually depends upon the frequency and
upon the manner in which the earphone is held to the ear.
.PP
Table 4/P.79 shows values obtained for one type of telephone held
fairly closely to the ear. Use of these values for calculation has given
reasonably good agreement with receiving and junction loudness ratings
determined by subjective measurements in the CCITT Laboratory. Such
calculations have used these values of \fIL\fR\d\fIE\fR\ufor both the IRS
and the
\*Qunknown\*U.
.PP
The values of \fIS\fR \s6\fIRJE\fR .PS 10
used to determine the values of \fIW\fR\d\fIs\fR\uin Table 2/P.79 include
a correction for \fIL\fR\d\fIE\fR\ucorresponding to
the values of Table 4/P.79. The values of \fIS\fR \s6\fIUJE\fR .PS 10
used in the calculation defined by Equations (4\(hy19a) and (4\(hy19c)
should also include a correction for \fIL\fR\d\fIE\fR\u, using either the
values of Table 4/P.79 or other values which might be considered more appropriate
for the conditions of use.
.RT
.PP
Note that the values of \fIL\fR\d\fIE\fR\uused for the
IRS have some effect on the calculated values of junction loudness rating.
This matter is receiving further study under Questions\ 8/XII\ [3] and
12/XII\ [4].
.RT
.ce
\fBH.T. [T4.79]\fR
.ce
TABLE\ 4/P.79
.ce
\fBValues of\fR
.ce
\fIL\fI
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
Frequency  (Hz)    \fIL\fI  (dB)    Frequency  (Hz)    \fIL\fI  (dB)
_
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
100    \ 20.0    1000    \(em2.3
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
125    \ 16.5    1250    \(em1.2
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
160    \ 12.5    1600    \(em0.1
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
200    \ 8.4    2000    \ 3.6
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
250    \ 4.9    2500    \ 7.4
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
315    \ 1.0    3150    \ 6.7
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
400    \(em0.7    4000    \ 8.8
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
500    \(em2.2    5000    \ 10.0
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
630    \(em2.6    6300    \ 12.5
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
800    \(em3.2    8000    \ 15.0
_
.TE
.nr PS 9
.RT
.ad r
\fBTable 4/P.79 [T4.79], p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
The transmission loss \fIx\fR\d\fIJ\fR\\d\fIJ\fR\uis the insertion loss between
600\(hyohms terminations of the chain of transmission elements between
JS and JR in Figure\ 1/P.79. Direct summation (with due respect to sign)
of this quantity with \fIS\fR \s6\fIUMJ\fR .PS 10
and \fIS\fR \s6\fIUJE\fR .PS 10
will not, in   general, give \fIL\fR \s6\fIUME\fR .PS 10
exactly because there are usually
some impedance mismatches. Care must therefore be taken to determine
\fIL\fR \s6\fIUME\fR .PS 10
correctly when calculating overall loudness
ratings. The inaccuracy will be severe when the transmission loss \fIx\fR\d\fIJ\fR\\d\fIJ\fR\uis
small and when the image impedances of the elements between JS and JR depart
considerably from 600\ ohms. The correct values for \fIL\fR \s6\fIUME\fR
.PS 10
can be obtained by direct measurement or by calculation taking all impedance
mismatches properly into account.
.bp
.RT
.sp 2P
.LP
\fB7\fR     \fBRestrictions of use\fR
.sp 1P
.RT
.PP
The calculation procedure described here and the values given for the parameters
are suitable for calculating sending, receiving and junction
loudness ratings. They may also be used for calculating overall loudness
ratings and
loudness insertion loss
provided the complete speech paths concerned are restricted to the telephone
frequency band, i.e.\ nominally to the range 300\(hy3400\ Hz.
.PP
They are not suitable for making comparisons between speech paths
having considerable differences in frequency band.
.PP
The values of the parameters have been chosen to give reasonably good agreement
with subjective loudness rating determinations by the CCITT
Laboratory using the method described in Recommendation\ P.78. The most
important utilization of Recommendation\ P.79 is a universally accepted
method for calculating the electro\(hyacoustic performance of telephone
sets. However,
Recommendation\ P.79 represents only with limited accuracy the speech and
hearing characteristics of \*Qordinary people\*U. This fact should be borne
in mind if a detailed circuit loudness analysis is attempted for a telephone
system.
For further information, see Supplement No.\ 19.
.RT
.sp 2P
.LP
\fB8\fR     \fBCalculation of sidetone masking rating\fR (STMR)
.sp 1P
.RT
.sp 1P
.LP
8.1
    \fICalculation from first principles\fR
.sp 9p
.RT
.PP
Recommendation P.76 describes the principles underlying the
sidetone masking rating method in which the human sidetone signal
\fIL\fR\d\fIM\fR\\d\fIE\fR\\d\fIH\fR\\d\fIS\fR\uis treated as a masking
threshold against which the
telephone sidetone path loss, \fIL\fR\d\fIm\fR\\d\fIe\fR\\d\fIS\fR\\d\fIT\fR\u,
is rated. As previously
reported the human sidetone path loss, \fIL\fR\d\fIM\fR\\d\fIE\fR\\d\fIH\fR\\d\fIS\fR\u,
has been
determined\ [5] and is shown graphically in Figure\ 4/P.76, and in tabular
form below in Table\ 5/P.79. Two sets of values are given in Table\ 5/P.79
for use
depending on whether the conditions of interest are for an earphone
coupling that is sealed (column\ 9) or with a typical leak included
(column\ 10).
.PP
The calculation method for STMR makes use of the same underlying
principles as described for sending and receiving loudness ratings
in \(sc\(sc\ 3 and\ 4. The calculation procedure is summarized by the
expression:
\v'6p'
.RT
.ce 1000
STMR =
@ { 0 } over { fIm\fR } @  log
\d10
\u
$$3o
@  int  @10
\u
@ { fImZ~l~\fR~+~10~log~\d1\u~\d0\u~\fIS\fR~`~\(*D~\fIf\fR } over { 0 } @
\d
$$3u
@  int  @10
\u
@ { fImZ\fR~+~10~log~\d1\u~\d0\u~\fIS\fR~`~\(*D~\fIf\fR } over { 0 } @
\d
$$3e
.ce 0
.ad r
(8\(hy1)
\v'2P'
.ad b
.RT
.LP
where
\v'6p'
.ce 1000
\fIZ\fR = \fIB\fR `\fI
\dS\u\fR \(em \fIL
\dmeST
\u\fR \(em \fIL
\dE\u\fR \(em 10 log
\d10
\u
@ left ( 10~\u { (*b~\d0\u~\(em\fIK\fR } over { 0 } \d~+~10~\u { fIB\fR~`\fI~S~\fR~~\(em~\fIL~MEHS~\fR } over { 0 } \d right ) @
.ce 0
.ad r
(8\(hy2)
\v'7p'
.ad b
.RT
.LP
.sp 1
and
\v'6p'
.ce 1000
\fIZ
\dl\u\fR = \fIB\fR `\fI
\dS\u\fR + \fIS
\dRmJ
\u\fR + \fIS
\dRJe
\u\fR \(em \fIL
\dE\u\fR \(em
10 log
\d10
\u
@ left ( 10~\u { (*b~\d0\u~\(em\fIK\fR } over { 0 } \d~+~10~\u { fIB\fR~`\fI~S~\fR~\(em~\fIL~MEHS~\fR } over { 0 } \d right ) @
.ce 0
.ad r
(8\(hy3)
\v'7p'
.ad b
.RT
.LP
.sp 1
.LP
where the quantities used are as defined in earlier sections but where,
for\ \fIm\fR , an index:
\v'6p'
.sp 1P
.ce 1000
\fIm\fR = 0.225
.ce 0
.sp 1P
.PP
.sp 1
The summations are normally extended over the range 100\ Hz to
8\ kHz but may be restricted if \fIL\fR\d\fIm\fR\\d\fIe\fR\\d\fIS\fR\\d\fIT\fR\ucannot
be satisfactorily
determined over the full bandwidth.
.PP
Table 5/P.79 lists the values for each of the quantities at the ISO
frequencies.
.bp
.RT
.ce
\fBH.T. [T5.79]\fR
.ce
TABLE\ 5/P.79
.ce
\fBListing of quantities necessary for the calculation of STMR\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(24p) | cw(18p) | cw(24p) | lw(18p) | lw(42p) | lw(18p) sw(24p) | lw(18p) | lw(42p) , ^  | ^  | ^  | ^  | ^  | l | l | ^ | ^ .
IRS    \fIS \dRmJ \u\fR       {
\fIS
\dRJe
\u\fR
\fIL\fI
\fIL
\dMEHS
\u\fR
 }

_
.TE
.TS
center box ;
lw(24p) | cw(18p) | cw(24p) | cw(18p) | cw(42p) | cw(18p) | cw(24p) | cw(18p) | cw(24p) | cw(18p) , ^  | ^  | c s | c | c | l | l | l.
Hz    dB    dB    1 pW/m\u2\d/Hz dB    dB    dB    dB    dB    1 V/Pa    1 Pa/V
        dB    Sealed    Un\(hy sealed
_
.T&
cw(24p) | cw(18p) | cw(24p) | cw(18p) | cw(42p) | cw(18p) | cw(24p) | cw(18p) | cw(24p) | cw(18p) .
(1)    (2)    (3)    (4)    (5)    (6)    (7)    (8)    (9)    (10)
.T&
cw(24p) | cw(18p) | cw(24p) | lw(18p) | lw(42p) | lw(18p) | lw(24p) | cw(18p) | cw(24p) | cw(18p) .
\ 1    \ 100    57.3    \ 17.5    \(em19.7    \(em45.8    \(em27.5    \ 20 |      \(em2.7    11.6
.T&
cw(24p) | cw(18p) | cw(24p) | lw(18p) | lw(42p) | lw(18p) | lw(24p) | cw(18p) | cw(24p) | cw(18p) .
\ 2    \ 125    60.2    \ 14.4    \(em18.8    \(em36.1    \(em18.8    \ 16.5    \(em4 |      10.6
.T&
cw(24p) | cw(18p) | cw(24p) | lw(18p) | lw(42p) | lw(18p) | lw(24p) | cw(18p) | cw(24p) | cw(18p) .
\ 3    \ 160    62.0    \ 10    \(em17.8    \(em25.6    \(em10.8    \ 12.5    \(em5.4    \ 7.1
.T&
cw(24p) | cw(18p) | cw(24p) | lw(18p) | lw(42p) | lw(18p) | lw(24p) | cw(18p) | cw(24p) | cw(18p) .
\ 4    \ 200    63.0    \ \ 5    \(em17    \(em19.2    \(em\ 2.7    \ 8.4    \(em2.7    \ 7.6
.T&
cw(24p) | cw(18p) | cw(24p) | lw(18p) | lw(42p) | lw(18p) | lw(24p) | cw(18p) | cw(24p) | cw(18p) .
\ 5    \ 250    63.0    \ \ 2.5    \(em16    \(em14.3    \ \ 2.7    \ 4.9    \(em2.8    \ 7.4
.T&
cw(24p) | cw(18p) | cw(24p) | lw(18p) | lw(42p) | lw(18p) | lw(24p) | cw(18p) | cw(24p) | cw(18p) .
\ 6    \ 315    62.4    \(em\ 0.4    \(em15.1    \(em10.8    \ \ 7.2    \ 1.0    \(em2.6    \ 6.1
.T&
cw(24p) | cw(18p) | cw(24p) | lw(18p) | lw(42p) | lw(18p) | lw(24p) | cw(18p) | cw(24p) | cw(18p) .
\ 7    \ 400    61.1    \(em\ 3    \(em14.4    \(em\ 8.4    \ \ 9.9    \(em0.7    \(em0.7    \ 3.5
.T&
cw(24p) | cw(18p) | cw(24p) | lw(18p) | lw(42p) | lw(18p) | lw(24p) | cw(18p) | cw(24p) | cw(18p) .
\ 8    \ 500    59.3    \(em\ 5    \(em13.6    \(em\ 6.9    \ 11.3    \(em2.2    \ 5 |      \ 5.7
.T&
cw(24p) | cw(18p) | cw(24p) | lw(18p) | lw(42p) | lw(18p) | lw(24p) | cw(18p) | cw(24p) | cw(18p) .
\ 9    \ 630    57.0    \(em\ 6.3    \(em13.3    \(em\ 6.1    \ 11.9    \(em2.6    \ 13.2    \ 8.9
.T&
cw(24p) | cw(18p) | cw(24p) | lw(18p) | lw(42p) | lw(18p) | lw(24p) | cw(18p) | cw(24p) | cw(18p) .
10    \ 800    54.4    \(em\ 8    \(em12.8    \(em\ 4.9    \ 12.3    \(em3.2    \ 19.9    16.2
.T&
cw(24p) | cw(18p) | cw(24p) | lw(18p) | lw(42p) | lw(18p) | lw(24p) | cw(18p) | cw(24p) | cw(18p) .
11    1000    51.5    \(em\ 9    \(em12.4    \(em\ 3.7    \ 12.6    \(em2.3    \ 26.1    23.8
.T&
cw(24p) | cw(18p) | cw(24p) | lw(18p) | lw(42p) | lw(18p) | lw(24p) | cw(18p) | cw(24p) | cw(18p) .
12    1250    48.4    \(em\ 8.5    \(em12.2    \(em\ 2.3    \ 12.5    \(em1.2    \ 23.7    23.7
.T&
cw(24p) | cw(18p) | cw(24p) | lw(18p) | lw(42p) | lw(18p) | lw(24p) | cw(18p) | cw(24p) | cw(18p) .
13    1600    45.4    \(em\ 8    \(em11.9    \(em\ 0.6    \ 13    \(em0.1    \ 22 |      22 |
.T&
cw(24p) | cw(18p) | cw(24p) | lw(18p) | lw(42p) | lw(18p) | lw(24p) | cw(18p) | cw(24p) | cw(18p) .
14    2000    42.3    \(em\ 9    \(em11.9    \ \ 0.3    \ 13.1    \ 3.6    \ 21.1    21.1
.T&
cw(24p) | cw(18p) | cw(24p) | lw(18p) | lw(42p) | lw(18p) | lw(24p) | cw(18p) | cw(24p) | cw(18p) .
15    2500    39.5    \(em11.5    \(em12    \ \ 1.8    \ 13.1    \ 7.4    \ 22.1    22.1
.T&
cw(24p) | cw(18p) | cw(24p) | lw(18p) | lw(42p) | lw(18p) | lw(24p) | cw(18p) | cw(24p) | cw(18p) .
16    3150    36.8    \(em13.8    \(em12.1    \ \ 1.8    \ 12.6    \ 6.7    \ 23.3    23.3
.T&
cw(24p) | cw(18p) | cw(24p) | lw(18p) | lw(42p) | lw(18p) | lw(24p) | cw(18p) | cw(24p) | cw(18p) .
17    4000    34.6    \(em13    \(em12.4    \(em37.2    \(em31.6    \ 8.8    \ 24.2    24.2
.T&
cw(24p) | cw(18p) | cw(24p) | lw(18p) | lw(42p) | lw(18p) | lw(24p) | cw(18p) | cw(24p) | cw(18p) .
18    5000    32.8    \(em12.5    \(em12.5    \(em52.2    \(em54.9    \ 10.0    (26)    (26)
.T&
cw(24p) | cw(18p) | cw(24p) | lw(18p) | lw(42p) | lw(18p) | lw(24p) | cw(18p) | cw(24p) | cw(18p) .
19    6300    31.5    \(em11.1    \(em13    \(em73.6    \(em67.5    \ 12.5    (28)    (28)
.T&
cw(24p) | cw(18p) | cw(24p) | lw(18p) | lw(42p) | lw(18p) | lw(24p) | cw(18p) | cw(24p) | cw(18p) .
20    8000    30.9    \(em\ 9    \(em14    \(em90    \(em90    \ 15.0    (30)    (30)
_
.TE
.nr PS 9
.RT
.ad r
\fBTable 5/P.79 [T5.79], p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
8.2
    \fICalculation of STMR using W weights\fR
.sp 9p
.RT
.PP
In \(sc 4 above, the fundamental principles underlying the loudness
rating procedure for sending, receiving, overall and junction loudness
ratings were further developed, and a simplified equation derived which
makes use of
the \fIW\fR weights listed in Table\ 2/P.79 together with simplified
equations\ (4\(hy19a) to\ (4\(hy19d). The equations\ (8\(hy1), (8\(hy2)
and\ (8\(hy3), applying to the STMR calculation, may also be reduced to
a simplified equation that makes use of a set of \fIW\fR weights and a
value of \fIm\fR unique to STMR,
thus:
\v'6p'
.RT
.ce 1000
STMR = \(em
@ { 0 } over { fIm\fR } @  log
\d10
\u
@ pile { fIN\fR above sum above 1 } @
10
\u(\fIm\fR /10)
(\(em \fIL\fR \fImeST\fR \(em \fIL\fR \fIE\fR
\(em \fIW\fR \fIM\fR
)
\d
.ce 0
.ad r
(8\(hy4)
\v'9p'
.ad b
.RT
.LP
.sp 1
.LP
or, if sidetone sensitivities have been measured:
\v'6p'
.ad r
\fB[F1.79], p.\fR
.ad b
.RT
.LP
where \fIm\fR = 0.225 and \fIW\fR\d\fIM\fR\u | take the values given in
Table 6/P.79.
.bp
.PP
In deriving \fIW\fR  | weights for the unsealed condition (column 3,
Table\ 6/P.79), values of \fIL\fR\d\fIE\fR\uin accordance with column\
8, Table\ 5/P.79 have been assumed for the reference path (IRS). When calculating
STMR unsealed,
appropriate values of \fIL\fR\d\fIE\fR\ushould be added to the \fIL\fR\d\fIm\fR\\d\fIe\fR\\d\fIS\fR\\d\fIT\fR\uvalues
and inserted in the formula as indicated. In many cases the \fIL\fR\d\fIE\fR\uvalues
of column\ 8, Table\ 5/P.79 will be satisfactory.
.PP
For the sealed condition the weights of column 2, Table 6/P.79 should be
used and the \fIL\fR\d\fIE\fR\uvalues associated with \fIL\fR\d\fIm\fR\\d\fIe\fR\\d\fIS\fR\\d\fIT\fR\u,
set to zero.
.RT
.ce
\fBH.T. [T6.79]\fR
.ce
TABLE\ 6/P.79
.ce
\fBWeighting factors for calculating STMR\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(48p) | cw(48p) | cw(48p) .
Band No.    \fIW\fI  sealed    \fIW\fI  unsealed
_
.T&
cw(48p) | cw(48p) | cw(48p) .
(1)    (2)    (3)
.T&
cw(48p) | cw(48p) | cw(48p) .
\ 1    110.4    94.0
.T&
cw(48p) | cw(48p) | cw(48p) .
\ 2    107.7    91.0
.T&
cw(48p) | cw(48p) | cw(48p) .
\ 3    104.6    90.1
.T&
cw(48p) | cw(48p) | cw(48p) .
\ 4    \ 98.4    86.0
.T&
cw(48p) | cw(48p) | cw(48p) .
\ 5    \ 94.0    81.8
.T&
cw(48p) | cw(48p) | cw(48p) .
\ 6    \ 89.8    79.1
.T&
cw(48p) | cw(48p) | cw(48p) .
\ 7    \ 84.8    78.5
.T&
cw(48p) | cw(48p) | cw(48p) .
\ 8    \ 75.5    72.8
.T&
cw(48p) | cw(48p) | cw(48p) .
\ 9    \ 66.0    68.3
.T&
cw(48p) | cw(48p) | cw(48p) .
10    \ 57.1    58.7
.T&
cw(48p) | cw(48p) | cw(48p) .
11    \ 49.1    49.4
.T&
cw(48p) | cw(48p) | cw(48p) .
12    \ 50.6    48.6
.T&
cw(48p) | cw(48p) | cw(48p) .
13    \ 51.0    48.9
.T&
cw(48p) | cw(48p) | cw(48p) .
14    \ 51.9    49.8
.T&
cw(48p) | cw(48p) | cw(48p) .
15    \ 51.3    49.3
.T&
cw(48p) | cw(48p) | cw(48p) .
16    \ 50.6    48.5
.T&
cw(48p) | cw(48p) | cw(48p) .
17    \ 51.0    49.0
.T&
cw(48p) | cw(48p) | cw(48p) .
18    \ 49.7    47.7
.T&
cw(48p) | cw(48p) | cw(48p) .
19    \ 50.0    48.0
.T&
cw(48p) | cw(48p) | cw(48p) .
20    \ 52.8    50.7
_
.TE
.nr PS 9
.RT
.ad r
\fBTable 6/P.79 [T6.79], p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
8.3
     \fIComments on sealed versus unsealed conditions for the calculation\fR
\fIof STMR\fR
.sp 9p
.RT
.PP
In deriving values of \fIL\fR\d\fIM\fR\\d\fIE\fR\\d\fIH\fR\\d\fIS\fR\u |
for the sealed ear, very stringent measures were taken to eliminate leaks
between the earcap of the test receiver and the subjects' ears. For \fIL\fR\d\fIM\fR\\d\fIE\fR\\d\fIH\fR\\d\fIS\fR\uunsealed
a particular value of \fIL\fR\d\fIE\fR\uwas acoustically inserted at the
receiver. The difference
between the \fIL\fR\d\fIM\fR\\d\fIE\fR\\d\fIH\fR\\d\fIS\fR\usealed and
\fIL\fR\d\fIM\fR\\d\fIE\fR\\d\fIH\fR\\d\fIS\fR\uwith leak can be seen by
comparing columns 9 and 10 of Table 5/P.79. Over the most important
parts of the frequency range this difference approximates to the value of
\fIL\fR\d\fIE\fR\uused at the receiver. In practice, rating differences
(sealed\(hyunsealed) are generally less than 1\ dB.
.PP
This suggests that in practice any leak present will affect
\fIL\fR\d\fIM\fR\\d\fIE\fR\\d\fIH\fR\\d\fIS\fR\uand \fIL\fR\d\fIM\fR\\d\fIE\fR\\d\fIS\fR\\d\fIT\fR\uapproximately
equally, at least
over a practical range of acoustic leaks. This in turn suggests that the
\fIL\fR\d\fIM\fR\\d\fIE\fR\\d\fIH\fR\\d\fIS\fR\uwill always have approximately
the same masking effect with respect to \fIL\fR\d\fIM\fR\\d\fIE\fR\\d\fIS\fR\\d\fIT\fR\uirrespective
of any leak present and that for
purposes of rating sidetone loudness STMR is expected to give better
correlation with subjective effects if calculated for sealed ear conditions.
.PP
Use of the sealed condition is preferred, but Administrations may
continue to use STMR unsealed for experimental purposes or where accumulation
of data makes it sensible to do so, e.g.\ for certain existing specifications.
If this is the case it must be clearly stated in the related
documentation.
.bp
.RT
.sp 1P
.LP
8.4
    \fICalculation of LSTR using W weights\fR
.sp 9p
.RT
.PP
Listener sidetone rating is calculated using the same algorithm as
STMR (Equation\ (8\(hy5)) but the sidetone sensitivity used is that derived
using a room noise source (see Recommendation\ P.64, \(sc\ 9). Thus:
\v'6p'
.RT
.ad r
\fB[F2.79], p.\fR
.ad b
.RT
.LP
where \fIm\fR = 0.225 and \fIW\fR\d\fIm\fR\u | take the values given in
Table\ 6/P.79.
.PP
LSTR may also be calculated by using a value of \fIS\fR\d\fIR\fR\\d\fIN\fR\\d\fIS\fR\\d\fIT\fR\u |
that has been determined by correcting \fIS\fR\d\fIm\fR\\d\fIe\fR\\d\fIS\fR\\d\fIT\fR\uby
\(*D\fI\fI\d\fIS\fR\\d\fIm\fR\u(see Recommendation\ P.10, Recommendation\
P.65 \(sc\ 9 and the Handbook on
Telephonometry, \(sc\ 3.3.17c), thus:
\v'6p'
.sp 1P
.ce 1000
\fIS\fR\d\fIR\fR\\d\fIN\fR\\d\fIS\fR\\d\fIT\fR\u\( = \fIS\fR\d\fIm\fR\\d\fIe\fR\\d\fIS\fR\\d\fIT\fR\u+
\(*D\fI\fI\d\fIS\fR\\d\fIm\fR\u.
.ce 0
.sp 1P
.PP
.sp 1
If this method is chosen, the sidetone sensitivity
\fIS\fR\d\fIm\fR\\d\fIe\fR\\d\fIS\fR\\d\fIT\fR\u | should also have been
determined using a wideband noise
source.
.PP
Annex A to Recommendation G.111 describes a method applicable to
transmission planning in which LSTR is determined by a STMR corrected by a
weighted value of \(*D\fI\fI\d\fIS\fR\\d\fIM\fR\u.
.PP
Information on other aspects of sidetone will be found in [6] and in the
Annex to Question\ 9/XII\ [7], in Recommendations\ G.121 and P.11, and
also in Supplement\ No.\ 11 at the end of this Volume.
.RT
.sp 2P
.LP
    \fBReferences\fR
.sp 1P
.RT
.LP
[1]
    CCITT\ \(em\ Question 19/XII, Contribution COM XII\(hyNo.\ 1, Study Period
1985\(hy1988, Geneva,\ 1985.
.LP
[2]
    CCITT\ \(em\ Question 7/XII, Contribution COM XII\(hyNo.\ 1, Study Period
1985\(hy1988, Geneva,\ 1985.
.LP
[3]
    CCITT\ \(em\ Question 8/XII, Contribution COM XII\(hyNo.\ 1, Study Period
1985\(hy1988, Geneva,\ 1985.
.LP
[4]
    CCITT\ \(em\ Question 12/XII, Contribution COM XII\(hyNo.\ 1, Study Period
1985\(hy1988, Geneva,\ 1985.
.LP
[5]
    CCITT\ \(em\ Contribution COM XII\(hyNo. 228/AP VII\(hyNo.115, Study Period
1977\(hy1980, Geneva,\ 1980.
.LP
[6]
    CCITT\ \(em\ Question 9/XII, Contribution COM XII\(hy234, Study Period
1981\(hy1984, Geneva,\ 1984.
.LP
[7]
    CCITT\ \(em\ Question 9/XII, Contribution COM XII\(hy1, Study period
1989\(hy1992, Geneva 1988.
.LP
.rs
.sp 15P
.ad r
Blanc
.ad b
.RT
.LP
.bp