home *** CD-ROM | disk | FTP | other *** search
Text File | 1991-12-13 | 63.0 KB | 2,277 lines |
- .rs
- .\" Troff code generated by TPS Convert from ITU Original Files
- .\" Not Copyright ( c) 1991
- .\"
- .\" Assumes tbl, eqn, MS macros, and lots of luck.
- .TA 1c 2c 3c 4c 5c 6c 7c 8c
- .ds CH
- .ds CF
- .EQ
- delim @@
- .EN
- .nr LL 40.5P
- .nr ll 40.5P
- .nr HM 3P
- .nr FM 6P
- .nr PO 4P
- .nr PD 9p
- .po 4P
-
- .rs
- \v | 5i'
- .sp 1P
- .ce 1000
- \v'3P'
- SECTION\ 5
- .ce 0
- .sp 1P
- .ce 1000
- \fBOBJECTIVE\ ELECTRO\(hyACOUSTICAL\ MEASUREMENTS\fR
- .ce 0
- .sp 1P
- .sp 2P
- .LP
- \fBRecommendation\ P.61\fR
- .RT
- .sp 2P
- .sp 1P
- .ce 1000
- \fBMETHODS\ FOR\ THE\ CALIBRATION\ OF\ CONDENSER\ MICROPHONES\fR
- .EF '% Volume\ V\ \(em\ Rec.\ P.61''
- .OF '''Volume\ V\ \(em\ Rec.\ P.61 %'
- .ce 0
- .sp 1P
- .ce 1000
- \fI(amended at Malaga\(hyTorremolinos, 1984)\fR
- .sp 9p
- .RT
- .ce 0
- .sp 1P
- .PP
- Primary and secondary calibrations of
- condenser
- microphones
- can be carried out using the methods described below.
- .sp 1P
- .RT
- .LP
- .sp 2P
- .LP
- \fB1\fR \fBPrimary calibration by the reciprocity method\fR
- .sp 1P
- .RT
- .PP
- The recommended procedure for primary calibration of condenser
- microphones is the
- reciprocity calibration technique
- . A precision
- method for reciprocity pressure calibration is described in\ [1]. A simplified
- method, suitable for calibration over the frequency range of interest for
- telephonometric measurements, is given in\ [2]. Although the methods described
- are specifically for
- one\(hyinch microphones
- , similar methods are
- applicable to
- half\(hyinch microphones
- . Methods suitable for half\(hyinch
- microphones are under study by IEC.
- .PP
- A precision method for free\(hyfield reciprocity calibration is given
- in\ [3]. Alternatively, the free\(hyfield correction curves given in\ [4]
- may be
- applied to the pressure calibration of one\(hyinch condenser microphones to
- determine their free\(hyfield responses. The reciprocity free\(hyfield
- calibration
- method may in principle be extended to half\(hyinch microphones. Free\(hyfield
- correction curves have not been standardized for half\(hyinch microphones.
- .RT
- .LP
- .sp 2P
- .LP
- \fB2\fR \fBSecondary calibration by the comparison method\fR
- .sp 1P
- .RT
- .PP
- The
- secondary calibration of a condenser microphone
- may be achieved by direct comparison with a physically identical microphone
- having a known calibration. The procedure used is a modification of the
- \*Qtwo microphones and auxiliary sound source\*U method described in\ [1]
- to\ [3]. The output of the calibrated microphone is first determined for
- a given drive level applied to
- the auxiliary sound source. The calibrated microphone is then replaced
- by the microphone to be calibrated, and its output is determined for the
- same drive
- level applied to the auxiliary sound source. The difference in level (in\ dB)
- between the outputs of the two microphones is then applied to the known
- calibration of the first microphone to determine the calibration of the
- second. The procedure is repeated at each frequency of interest.
- .RT
- .sp 2P
- .LP
- \fB3\fR \fBSecondary calibration using \fR \fBpistonphones\fR \fBand other\fR
- \fBsound level calibrators\fR
- .sp 1P
- .RT
- .PP
- Secondary calibrations can also be made using pistonphones and
- other sound level calibrators which produce a known sound level. Such
- .PP
- devices are often used to check the calibration of a microphone at a single
- frequency
- .FS
- Calibrations with an accuracy of \(+- | .3\ dB are possible.
- .FE
- .
- Care should be taken to follow the manufacturer's instructions when using
- such devices; in particular, it may be necessary to apply corrections for
- barometric pressure, coupler volume, microphone type, etc. Standardization
- of these
- calibrators is currently under study by the IEC.
- .bp
- .RT
- .sp 2P
- .LP
- \fBReferences\fR
- .sp 1P
- .RT
- .LP
- [1]
- International Electrotechnical Commission \fIPrecision method for\fR
- \fIpressure calibration of one\(hyinch standard condenser microphones by
- the\fR
- \fIreciprocity technique\fR , IEC publication\ 327, Geneva,\ 1971.
- .LP
- [2]
- International Electrotechnical Commission \fISimplified method for\fR
- \fIpressure calibration of one\(hyinch condenser microphones by the reciprocity\fR
- \fItechnique\fR , IEC publication\ 402, Geneva,\ 1972.
- .LP
- [3]
- International Electrotechnical Commission \fIPrecision method for\fR
- \fIfree\(hyfield calibration of one\(hyinch standard condenser microphones
- by the\fR
- \fIreciprocity technique\fR , IEC publication\ 486, Geneva,\ 1974.
- .LP
- [4]
- International Electrotechnical Commission \fIValues for the difference\fR
- \fIbetween free\(hyfield and pressure sensitivity levels for one\(hyinch
- standard\fR
- \fIcondenser microphones\fR , IEC Publication\ 655, Geneva,\ 1979.
- \v'2P'
- .sp 2P
- .LP
- \fBRecommendation\ P.62\fR
- .RT
- .sp 2P
- .sp 1P
- .ce 1000
- \fBMEASUREMENTS\ ON\ SUBSCRIBERS'\ TELEPHONE\ EQUIPMENT\fR
- .EF '% Volume\ V\ \(em\ Rec.\ P.62''
- .OF '''Volume\ V\ \(em\ Rec.\ P.62 %'
- .ce 0
- .sp 1P
- .ce 1000
- \fI(amended at Malaga\(hyTorremolinos, 1984 and Melbourne, 1988)\fR
- .sp 9p
- .RT
- .ce 0
- .sp 1P
- .LP
- \fB1\fR \fBMeasurement of the attenuation distortion of a telephone
- set\fR
- .sp 1P
- .RT
- .PP
- The curve of the variation of the absolute sensitivity of an item of telephone
- equipment (sending or receiving system) as a function of frequency does
- not supply complete information on the manner in which this equipment
- reproduces the human voice or music, although such a curve may often be
- called the frequency characteristic.
- .PP
- However, the curve of variation of the absolute sensitivity of
- telephone equipment as a function of frequency gives useful indications from
- the point of view of the transmission of speech. On the other hand, for the
- transmission of music, in the absence of a precise criterion of the quality
- of transmission (corresponding to articulation, or repetition rate, in
- commercial telephony) such curves should be sufficient to enable the quality
- of the terminal equipment used (microphone or loudspeakers) to be appreciated.
- .PP
- For tracing sensitivity/frequency characteristics the methods described
- in Recommendation\ P.64 and its associated Annex\ B may be used.
- .RT
- .sp 2P
- .LP
- \fB2\fR \fBMeasurement of the nonlinear distortion of a telephone set\fR
- \fBand of microphone noise\fR
- .sp 1P
- .RT
- .PP
- While the nonlinear distortion of telephone receivers is in general negligible,
- microphones (and particularly carbon microphones of the type
- generally used in commercial telephone equipment) show considerable
- nonlinearity: the relationship between the variation of microphone resistance
- and the acoustic pressure on the diaphragm is not linear. This nonlinearity
- .PP
- becomes more important as the variation of resistance in relation to the
- total resistance of the microphone increases, i.e. when the microphone
- is more
- sensitive. Furthermore, there may be two supplementary effects:
- .RT
- .LP
- 1)
- The microphone is less sensitive to acoustic pressure lower than a certain
- value (threshold of excitation).
- .LP
- 2)
- As a consequence of the mechanical inertia of the
- carbon granules (delay in establishing electrical contact
- between the granules), the various states of agitation of the
- carbon under the influence of acoustic waves are not the same
- for all frequencies (for example, slow beats between two sounds
- are in general enhanced in reproduction by a carbon microphone).
- .bp
- .PP
- Existing information on the general effect of harmonic distortion on telephone
- speech quality indicates that the effect of second order
- distortion is considerably less than that of third order distortion. Absolute
- detection thresholds obtained in different test are, however, difficult
- to
- compare because of differences in definition and measurement of the
- distortion.
- .PP
- \fINote\ 1\fR \ \(em\ Summaries of information available in this area are
- given in\ [1] and\ [2]. It is clear that measurements with sinusoidal signals
- can
- predict the speech transmission performance of nonlinear systems only to a
- limited extent, particularly if the peak value of the test signal is much
- smaller than the transmitted speech signal. A complex signal having the same
- spectral density at the same amplitude density function as real speech,
- see Recommendation\ P.50, is therefore expected to be a more useful test
- signal.
- .PP
- \fINote\ 2\fR \ \(em\ The application of complex test signals or actual speech
- signals for the measurement of nonlinearity in telephone circuits is studied
- under Question\ 13/XII\ [3].
- .PP
- Certain types of carbon microphones may produce an audible stationary noise,
- often depending on the size of feeding current. The measurement of this
- kind of noise and its effect on transmission quality is the same as for
- other kinds of additive circuit noise.
- .RT
- .sp 2P
- .LP
- \fB3\fR \fBObjective measurement of loudness rating (LR)\fR
- .sp 1P
- .RT
- .PP
- Examples of apparatus that objectively measure LRs conforming to
- Recommendation\ P.65 are \*QCERF\*U of the French Administration\ [4],
- \*QAURAL\*U of
- NTT\ [5], \*QTIGGER\*U\ [6] of British Telecom and \*QLoudness Rating Meter\*U\
- [7] of
- STL. Short descriptions of the apparatus named above can be found in Chapter\
- 5 of the CCITT \fIHandbook on Telephonometry\fR \ [8].
- .RT
- .sp 2P
- .LP
- \fBReferences\fR
- .sp 1P
- .RT
- .LP
- [1]
- CCITT\ \(em\ Question 13/XII, Annex 1, Contribution COM XII\(hyNo.1,
- Study\ Period\ 1981\(hy1984, Geneva,\ 1981.
- .LP
- [2]
- CCITT\ \(em\ Question 13/XII, Annex, Green Book, Vol. V, ITU, Geneva,\ 1973.
- .LP
- [3]
- CCITT\ \(em\ Question 13/XII, Contribution COM XII\(hyNo. 1,
- Study\ Period\ 1985\(hy1988, Geneva,\ 1985.
- .LP
- [4]
- CCITT\ \(em\ Contribution COM XII\(hyNo. 184, \fIEquipment for the objective\fR
- \fImeasurement of equivalent R25 and of the sidetone\ \(em\ used by the
- French\fR
- \fIAdministration\fR (France), Study\ Period\ 1981\(hy1984.
- .LP
- [5]
- CCITT\ \(em\ Contribution COM XII\(hyNo. 79, \fIObjective loudness rating\fR
- \fImeasurement system\fR , (NTT), Study\ Period\ 1981\(hy1984.
- .LP
- [6]
- WARD (H. | .) and CROSS (R. | .) TIGGER: An Automatic Test System for
- measuring the Transmission Performance of Telephones, \fIBritish\fR
- \fITelecommunications Engineering\fR , Volume\ 2, July\ 1983.
- .LP
- [7]
- CCITT\ \(em\ Question 15/XII, Annex 6, Contribution COM\(hyNo. 1,
- Study Period\ 1985\(hy1988.
- .LP
- [8]
- CCITT \fIHandbook on Telephonometry\fR , UIT, Geneva,\ 1987.
- \v'1P'
- .sp 2P
- .LP
- \fBRecommendation\ P.63\fR
- .RT
- .sp 2P
- .ce 1000
- \fBMETHODS\ FOR\ THE\ EVALUATION\ OF\ TRANSMISSION\ QUALITY\fR
- .EF '% Volume\ V\ \(em\ Rec.\ P.63''
- .OF '''Volume\ V\ \(em\ Rec.\ P.63 %'
- .ce 0
- .sp 1P
- .ce 1000
- \fBON\ THE\ BASIS\ OF\ OBJECTIVE\ MEASUREMENTS\fR
- .ce 0
- .sp 1P
- .PP
- These measuring methods are being studied by the CCITT under
- Question\ 7/XII [1]. Annexes\ A and\ B to Recommendation\ P.11 and Supplements
- No.\ 2 and\ 3, at the end of this Fascicle, describe methods used respectively
- by British Telecom and\ AT&T. Attention is also drawn to methods for calculating
- loudness ratings given in Recommendation\ P.79.
- .sp 1P
- .RT
- .sp 2P
- .LP
- \fBReference\fR
- .sp 1P
- .RT
- .LP
- [1]
- CCITT\ \(em\ Question 7/XII, Contribution COM XII\(hyNo.\ 1,
- Study\ Period\ 1985\(hy1988, Geneva,\ 1985.
- .bp
- .sp 2P
- .LP
- \fBRecommendation\ P.64\fR
- .RT
- .sp 2P
- .ce 1000
- \fBDETERMINATION\ OF\fR \fB\ SENSITIVITY/FREQUENCY\ CHARACTERISTICS\fR
- .EF '% Volume\ V\ \(em\ Rec.\ P.64''
- .OF '''Volume\ V\ \(em\ Rec.\ P.64 %'
- .ce 0
- .ce 1000
- \fBOF\ LOCAL\ TELEPHONE\ SYSTEMS\fR \fB\ TO\ PERMIT\ CALCULATION\ \fR
- .ce 0
- .sp 1P
- .ce 1000
- \fBOF\ THEIR\ LOUDNESS\ RATINGS\fR
- .ce 0
- .sp 1P
- .ce 1000
- \fI(Geneva, 1976; amended at Malaga\(hyTorremolinos, 1984\fR
- .sp 9p
- .RT
- .ce 0
- .sp 1P
- .ce 1000
- \fIand Melbourne, 1988)\fR
- .ce 0
- .sp 1P
- .PP
- See Recommendation\ P.76 for general principles concerning the
- determination of loudness ratings.
- .sp 1P
- .RT
- .LP
- .sp 2P
- .LP
- \fB1\fR \fBIntroduction\fR
- .sp 1P
- .RT
- .PP
- The sending, receiving or sidetone sensitivity/frequency
- characteristic of a local telephone system (LTS) is usually measured
- directly.
- .PP
- \fINote\ 1\fR \ \(em\ The sending, receiving or sidetone sensitivity/frequency
- characteristic can also be calculated provided the relevant information
- of the telephone line and feeding bridge is known. Some of the information
- required
- for sidetone is outside the scope of the existing Recommendations.
- .PP
- \fINote\ 2\fR \ \(em\ The same principles also apply to the measurement of
- microphones and earphones.
- .PP
- Since
- electro\(hyacoustical measurements
- of the type being
- considered may be required for different purposes, it is important to
- distinguish the following:
- .RT
- .LP
- a)
- supplying the designer of a
- transducer
- with
- information concerning the success he has achieved in aiming at a
- given sensitivity/frequency response;
- .LP
- b)
- checking that the manufactured product meets the specified requirements;
- .LP
- c)
- supplying sensitivity/frequency characteristics suitable for use in calculating
- loudness ratings, or estimating other
- subjectivity\(hydetermined quantities.
- .PP
- The present Recommendation is concerned only with c) and, for this purpose,
- measurements under real conditions must form the basis. Artificial
- mouths and artificial ears must be used with due regard to obtaining good
- agreement between these measurements and those from real mouth and ear
- determinations. Measurements under real conditions are complicated,
- time\(hyconsuming and not reproducible with great precision, especially when
- carbon microphones are involved.
- .PP
- The present Recommendation describes measurement methods using
- recommended forms of artificial mouths and artificial ears (see
- Recommendation\ P.51).
- .PP
- This Recommendation applies mainly to LTSs with handset telephones.
- However, the principles also apply to other types of telephones. Specific
- considerations for headsets are described in Recommendation\ P.38, and for
- loudspeaker telephones in Recommendation\ P.34.
- .RT
- .sp 2P
- .LP
- \fB2\fR \fBSending sensitivities of the LTS\fR
- .sp 1P
- .RT
- .PP
- For the present purposes, the sending sensitivity of a local
- telephone system is specified in terms of the free\(hyfield sound
- pressure at a reference point in front of the mouth
- .FS
- The mouth reference
- point used in the present Recommendation is defined in Annex\ A.
- .FE
- , and the electrical output from the local telephone system or the microphone
- as the case may be. The input sound pressure cannot be measured simultaneously
- with the
- electrical output and therefore the measurement must be made in an indirect
- manner. The sound pressure at the reference point is measured in the absence
- of the handset and, with the artificial mouth source unchanged, the handset
- is
- placed in the defined position in front of the mouth and the output measured.
- When a human mouth and voice are used, the source cannot be relied upon
- to
- maintain its output constant between the measurement of free\(hyfield sound
- pressure and that of the electrical output from the microphone. Artificial
- mouths suffer from imperfect representation of the source impedance and
- field distribution that applies to real mouths.
- .bp
- .RT
- .PP
- In addition to providing the proper source conditions, it is
- necessary to ensure that the mouthpiece is located for every design of
- telephone handset at the position that would be used in the real situation.
- This can be achieved by locating the
- mouthpiece
- properly with respect to an ear reference point; this ensures that longer
- handsets are measured with a greater
- mouth\(hyto\(hymicrophone distance
- than is the case for shorter
- handsets. The success of using a given handset measuring position for
- measurement of sensitivity/frequency characteristics can be judged only by
- making comparisons, for handsets of different lengths, between real
- conversation test results using the artificial mouth and real mouths under
- suitably controlled measuring conditions. For the present Recommendation,
- the telephone handset shall be located as defined in Annex\ A of
- Recommendation\ P.76.
- .PP
- Special problems are encountered when making measurements with real
- mouths and real voices, even under controlled talking conditions. Under such
- circumstances the sound pressure cannot be measured directly at the required
- mouth reference point
- and therefore it has to be measured at some other point and referred indirectly
- to the mouth reference point. Some previous
- determinations have made use of a measuring microphone 1\ metre from the
- mouth but this requires anechoic surroundings and is affected by obstruction
- from the handset under test. Other methods have been also tried and none
- seems
- satisfactory so far.
- .PP
- When the sound pressure input to a carbon microphone is increased, the
- corresponding increase in output voltage does not bear a linear relationship
- to the increase in sound pressure. This nonlinearity is a very complicated
- function of applied sound pressure, frequency, feeding current, conditioning
- and
- granule\(hychamber
- orientation. Reproducible results are obtained with an artificial mouth
- only if proper attention is paid to all these factors.
- .RT
- .sp 2P
- .LP
- \fB3\fR \fBReceiving sensitivities of the LTS\fR
- .sp 1P
- .RT
- .PP
- The IEC\(hy318 model artificial ear (see Recommendation\ P.51)
- provides means for precise measurements of the receiving sensitivities
- of the LTS. However, the sound pressures measured with it do not always
- agree well with those existing at the
- ear reference point
- in real ears under the test conditions used when subjective determinations
- of loudness ratings are being made. This can be attributed partly to the
- presence of appreciable
- acoustical leakage
- (\fIL\fR\d\fIE\fR\u) between the earphone and the real
- ear (such leakage is not represented in available recommended forms of the
- artificial ear) and partly to an increase in enclosed volume between the
- forms of earphone and the forms of real ear. Therefore, to use the results
- of
- measurements made according to the present Recommendation, it is necessary
- to make a correction (see \(sc\ 7\ below).
- .PP
- \fR Clearly, it would be very desirable if the artificial ear could be
- modified so as to avoid the need for the correction. Some further work
- has been done on this matter but it is not yet clear whether a single modification
- to
- the artificial ear would suffice for all types of telephone earphone. Further
- evidence is required, preferably from several laboratories so that a much
- wider variety of types of earphone can be examined.
- .RT
- .sp 2P
- .LP
- \fB4\fR \fBArtificial mouth and voice\fR
- .sp 1P
- .RT
- .PP
- The following properties are required:
- .RT
- .LP
- a)
- the distribution in sound pressure around the orifice must be a good
- approximation to that around a human mouth;
- .LP
- b)
- the acoustical impedance looking into the mouth must
- simulate that for human mouths, so that the pressure increase caused by
- the obstruction effect of telephone microphones will be representative;
- .LP
- c)
- it must be possible to establish definite sound pressures at the mouth
- reference point as a function of frequency. A convenient
- feature to embody in a practical artificial mouth is the
- linearity, over a suitable range of sound pressures, of the ratio
- of sound pressure at the mouth reference point to the voltage
- input to the artificial mouth. The ratio must be independent of
- frequency at least over the range 200\ to 4000\ Hz but preferably 100\ to
- 8000\ Hz.
- .PP
- For the present purposes the mouth reference point (MRP) is
- defined by the point on the axis of the artificial mouth located 25\ mm
- in front of the
- equivalent lip position
- (see Annex\ A).
- .PP
- Recommendation\ P.51 defines the requirements for artificial mouths.
- .PP
- \fINote\fR \ \(em\ However, the send loudness ratings calculated from the
- sending sensitivities measured when using an artificial mouth do not always
- agree well with the loudness ratings determined subjectively using real
- mouths. The subject is still under study in Questions\ 8/XII and\ 12/XII.
- .bp
- .PP
- In principle, the artificial voice defined in Recommendation\ P.50
- should be used as the
- acoustic test signal
- . However, sine waves at
- defined frequencies have been used satisfactorily so far as stable sets are
- concerned. Some other signals with continuous spectra, for example pink
- noise and Gaussian noise having the same long\(hyterm spectrum as speech,
- can also be
- used as the acoustic test signal. Sine waves can also be used for the
- measurement of some types of carbon microphones if appropriate techniques
- are used (see Annex\ B).
- .RT
- .sp 2P
- .LP
- \fB5\fR \fBArtificial ear\fR
- .sp 1P
- .RT
- .PP
- The following properties are required:
- .RT
- .LP
- a)
- the acoustical impedance presented to telephone earphones
- must simulate that presented by real ears under practical
- conditions of use of telephone handsets;
- .LP
- b)
- the sensitivity of the artificial ear is defined as the
- pressure sensitivity of the measuring microphone. It should be
- constant within \(+- | .5\ dB over the frequency range
- 100\(hy8000\ Hz.
- .PP
- For a human ear, the ear reference point (ERP) is defined in
- Annex\ A. The corresponding point when the ear\(hycap is fitted to an artificial
- ear will usually differ from the place at which the sound pressure is measured
- and for this and other reasons certain corrections are necessary when the
- results are used for calculating loudness ratings (see \(sc\ 3\ above).
- .LP
- .sp 2P
- .LP
- \fB6\fR \fBDefinition of sending sensitivity of an LTS\fR
- .sp 1P
- .RT
- .PP
- The sending sensitivity of an LTS, depends
- upon the location of the handset relative to the equivalent lip position
- of the artificial mouth. For the present purposes the
- speaking position
- defined in Annex\ A to Recommendation\ P.76 shall be used. Usually, the
- sending sensitivity is a function of frequency.
- .PP
- The sending sensitivity of a local telephone system at a specified
- frequency or in a narrow frequency band is expressed as follows:
- \v'6p'
- .RT
- .sp 1P
- .ce 1000
- \fIS
- \dmJ
- \u\fR = 20 log
- \d10
- \u
- @ { fIV~\dJ\u\fR } over { fIp~\dm\u\fR } @ dB
- rel 1 V/Pa
- .ce 0
- .sp 1P
- .LP
- .sp 1
- .LP
- where \fIV\fR\d\fIJ\fR\uis the voltage across a 600\ ohms termination and
- \fIp\fR\d\fIm\fR\uis the sound pressure at the mouth reference point. Note
- that \fIp\fR\d\fIm\fR\umust be measured in the absence of the \*Qunknown\*U
- handset of the test item.
- .sp 1P
- .LP
- 6.1
- \fIMeasurement of telephone sets containing\fR \fIcarbon microphones\fR
- .sp 9p
- .RT
- .PP
- It is intended that the Recommendation should apply for measuring systems
- containing carbon microphones as well as those having noncarbon
- microphones. When measuring LTSs that contain linear items, it does not
- matter at which sound pressure the measurements are made as long as it
- is known and
- does not cause overloading. However, when carbon microphones are present,
- different sensitivities will be obtained depending upon the sound pressure
- and characteristics of the acoustic signal used. For calculation of sending
- loudness rating, these must be reduced to single values at each frequency
- and the method of reduction must take account of the characteristics of
- human
- speech. At present, there is no single method that can be recommended for
- universal use. The problem is being studied under Question\ 8/XII\ [1].
- Until a suitable method can be defined, Administrations may take note of
- the various
- methods that have been suggested and are undergoing appraisal; they are
- indicated in Annex\ B.
- .RT
- .LP
- .sp 2P
- .LP
- \fB7\fR \fBDefinition of receiving sensitivity of an LTS\fR
- .sp 1P
- .RT
- .PP
- Usually, the receiving sensitivity is a function of frequency. The receiving
- sensitivity of a local telephone system at a specified frequency or in
- a narrow frequency band, as measured directly with an artificial ear
- complying with Recommendation\ P.51, is expressed as follows:
- \v'6p'
- .RT
- .sp 1P
- .ce 1000
- \fIS
- \dJe
- \u\fR = 20 log
- \d10
- \u
- @ { fIp~\de\u\fR } over { (12~\fIE~\dJ\u\fR } @ dB
- rel 1 Pa/V
- .ce 0
- .sp 1P
- .LP
- .sp 1
- where \fIp\fR\d\fIe\fR\uis the sound pressure in the artificial ear and
- \(12\ \fIE\fR\d\fIJ\fR\uis half the emf in the 600\ ohm source.
- .bp
- .PP
- \fINote\fR \ \(em\ The receiving sensitivity suitable for use in calculation
- of loudness is given by:
- \v'6p'
- .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
- where \fIL\fR\d\fIE\fR\uis a correction explained above in \(sc\ 3 and
- \fIS\fR\d\fIJ\fR\\d\fIE\fR\uis the
- receiving sensitivity determined using a large number of real ears.
- .PP
- Further information on this topic is given in
- Recommendation\ P.79.
- .sp 2P
- .LP
- \fB8\fR \fBDefinitions of\fR
- \fBtalker and listener sidetone sensitivities of an LTS\fR
- .sp 1P
- .RT
- .PP
- The talker sidetone sensitivity of an LTS is a function of the
- sending and receiving sensitivities of the telephone set, but also depends
- on a number of factors including the local subscriber's line conditions,
- the
- effective terminating impedance at the local exchange and the sidetone
- balance circuit within the telephone set.
- .PP
- The sidetone sensitivity as measured from an artificial mouth to the telephone
- earphone is expressed as:
- \v'6p'
- .RT
- .sp 1P
- .ce 1000
- \fIS
- \dmeST
- \u\fR = 20 log
- \d10
- \u
- @ left ( { fIp~\de\u\fR } over { fIp~\dm\u\fR } right ) @ \ \ dB
- .ce 0
- .sp 1P
- .LP
- .sp 1
- where \fIp\fR\d\fIm\fR\uis defined in \(sc\ 6 and \fIp\fR\d\fIe\fR\uis
- the sound pressure developed in the artificial ear with the handset in
- the loudness rating guard ring position (LRGP).
- .PP
- The listener sidetone sensitivity as measured in a diffuse room
- noise field is expressed as:
- \v'6p'
- .sp 1P
- .ce 1000
- \fIS
- \dRNST
- \u\fR = 20 log
- \d10
- \u
- @ left ( { fIp~\de\u\fR } over { fIp~\dRN~\u\fR~ } right ) @ \ \ dB
- .ce 0
- .sp 1P
- .LP
- .sp 1
- .LP
- where \fIp\fR\d\fIe\fR\uis the sound pressure developed in the artificial
- ear with the
- handset held at LRGP in front of an unenergised artificial mouth, for a
- diffuse room noise sound pressure \fIp\fR\d\fIR\fR\\d\fIN\fR\umeasured
- at the MRP, but in the absence of all obstacles (e.g.\ test head, handset,\
- etc.).
- .sp 2P
- .LP
- \fB9\fR \fBMethods for determining S\fR\(da\fBm\fR\(da\fBJ\fR \fB, S\fR\(da\fBJ\fR\(da\fBe\fR
- \fB,
- S\fR\(da\fBm\fR\(da\fBe\fR\(da\fBS\fR\(da\fBT\fR \fB, S\fR\(da\fBR\fR\(da\fBN\fR\(da\fBS\fR\(da\fBT
- and \(*D\fR\(da\fBS\fR\(da\fBM\fR
- .sp 1P
- .RT
- .PP
- When the sending, receiving and sidetone sensitivities of an actual local
- telephone system are required, the\ measurements according to the
- definitions given in \(sc\(sc\ 6, 7 and\ 8 above can be made as illustrated in
- Figures\ 1/P.64, 2/P.64, 3/P.64, 4/P.64 and\ 5/P.64. These methods have
- been used by CCITT Laboratory and elsewhere successfully.
- .PP
- When using fast Fourier transform (FFT) techniques for measuring the characteristics
- of non\(hylinear LTS, the measurement principle used, i.e.\ ratio of r.m.s.
- variables, or crosspectrum (coherent) method, should be specified.
- .PP
- More detail may be found in Section 3 of the \fIHandbook of\fR
- \fITelephonometry\fR \ [2].
- .PP
- Figure 1/P.64 shows the method of setting up the artificial mouth so that
- the sound pressure \fIp\fR\d\fIm\fR\uat the mouth reference point is known
- at each test frequency or frequency band. It is recommended to provide
- equalization in the artificial mouth drive circuit to maintain the free\(hyfield
- sound pressure
- constant at the MRP to within \(+- | \ dB over the frequency range\ 100
- to 8000\ Hz. In no case should the deviation exceed \(+- | \ dB over the
- frequency range\ 200 to 4000\ Hz and +2/\(em5\ dB over the frequency range\
- 100 to\ 8000\ Hz. It is
- recommended that any deviations from the desired sound pressure level be
- taken into account when determining the sending or sidetone sensitivity
- of a local
- telephone system. This is particularly true if the deviation exceeds
- \(+- | \ dB.
- .PP
- For any test signal, \fIp\fR\d\fIm\fR\uof \(em4.7 dBPa is recommended (see
- Note 2 to Annex\ B for information).
- .bp
- .RT
- .LP
- .rs
- .sp 16P
- .ad r
- \fBFIGURE\ 1/P.64, p.\fR
- .sp 1P
- .RT
- .ad b
- .RT
- .PP
- Figure\ 2/P.64 shows the measurement of output \fIV\fR\d\fIJ\fR\ufrom the
- local telephone system when the handset is placed at the
- appropriate position in front of the artificial mouth and the artificial
- mouth is energized in the same manner as when the sound pressure \fIp\fR\d\fIm\fR\uwas
- set up in the absence of the handset under test (see Figure\ 1/P.64).
- .LP
- .rs
- .sp 17P
- .ad r
- \fBFIGURE\ 2/P.64 p.\fR
- .sp 1P
- .RT
- .ad b
- .RT
- .PP
- Figure\ 3/P.64 shows the measurement of the sound pressure \fIp\fR\d\fIe\fR\uin
- the artificial ear when the local telephone system is connected to
- a 600\(hyohm source of internal emf \fIE\fR\d\fIJ\fR\u. Note that the definition
- of
- \fIS\fR\d\fIJ\fR\\d\fIe\fR\uis in terms of 1/2\ \fIE\fR\d\fIJ\fR\uand not
- the potential difference across the input terminals of the local telephone
- system; this potential difference
- will, of course, differ from 1/2\ \fIE\fR\d\fIJ\fR\u, if the input impedance
- of the local telephone system is not 600\ ohms. Care must be taken to ensure
- that there is no coupling loss (acoustic leakage) between the ear\(hypiece
- of the receiving system under test and the artificial ear. Usually \fIE\fR\d\fIJ\fR\u\
- =\ \(em12\ dBV is
- recommended.
- .PP
- \fINote\fR \ \(em\ Some receiving systems incorporate electronic circuits to
- provide special features, for example, compression to limit the level of the
- received sound signal. Particular care must be exercised during the measurement
- of such systems to ensure that the resulting sensitivity is correct and
- relevant. In some cases it may be necessary to determine the receiving
- sensitivity over a range of input levels.
- .bp
- .RT
- .LP
- .rs
- .sp 17P
- .ad r
- \fBFIGURE\ 3/P.64, p.\fR
- .sp 1P
- .RT
- .ad b
- .RT
- .PP
- Figure 4/P.64 shows the measurement of sidetone sensitivity. The resulting
- value of \fIS\fR\d\fIm\fR\\d\fIe\fR\\d\fIS\fR\\d\fIT\fR\uis highly dependent
- on the impedance
- connected to the telephone set terminals and therefore, under short line
- conditions, on the exchange termination. As this impedance often deviates
- considerably from 600\ ohms, particularly when there is a complete connection
- present, 600\ ohms is given only as an example.
- .LP
- .rs
- .sp 22P
- .ad r
- \fBFIGURE\ 4/P.64, p.\fR
- .sp 1P
- .RT
- .ad b
- .RT
- .LP
- .bp
- .LP
- \fB
- .PP
- The determination of the room noise sidetone sensitivity
- \fIS
- \dRNST
- \u\fR is illustrated in Figure\ 5/P.64. For this measurement, sine
- wave signals are unsuitable and it is necessary to make use of continuous
- spectrum sound having, for example, a Hoth or pink noise spectrum (see
- \(sc\ B.3). First, the magnitude of the diffuse field \fIp\fR\d\fIR\fR\\d\fIN\fR\uis
- determined and then
- the sound pressure at the artificial ear is measured.
- .RT
- .LP
- .rs
- .sp 35P
- .ad r
- \fBFigure 5/P.64, p.\fR
- .sp 1P
- .RT
- .ad b
- .RT
- .PP
- Using the above method, the sound pressure developed at the artificial
- ear usually is very low. An alternative way to determine \fIS
- \dRNST
- \u\fR is to measure the sending sensitivity \fIS\fR\d\fIm\fR\\d\fIJ\fR\uusing
- an artificial mouth and one of the methods in Annex\ B, using a continuous
- spectrum signal (e.g.\ \(sc\(sc\ B.3,
- B.4)
- and then to measure the room noise sending sensitivity \fIS
- \dmJ\fR /\fIRN
- \u\fR using a diffuse field method such as described for room noise sidetone
- sensitivity
- above. (A detailed description of the method is given in the Handbook on
- Telephonometry).
- .bp
- .PP
- The definition of \(*D\fI\fI\d\fIS\fR\\d\fIM\fR\uis
- \v'6p'
- .RT
- .sp 1P
- .ce 1000
- \(*D\fI\fI\d\fIS\fR\\d\fIM\fR\u= \fIS
- \dMJ\fR /\fIRN
- \u\fR \(em \fIS\fR\d\fIM\fR\\d\fIJ\fR\u
- .ce 0
- .sp 1P
- .LP
- .sp 1
- .LP
- where \fIS\fR\d\fIM\fR\\d\fIJ\fR\uis the real voice sensitivity.
- .PP
- However, for all practical purposes, when using the artificial
- mouth, we may consider that \(*D\fI\fI\d\fIS\fR\\d\fIM\fR\uis equal
- to\ \(*D\fI\fI\d\fIS\fR\\d\fIm\fR\u:
- \v'6p'
- .sp 1P
- .ce 1000
- \(*D\fI\fI\d\fIS\fR\\d\fIm\fR\u= \fIS
- \dmJ\fR /\fIRN
- \u\fR \(em \fIS\fR\d\fIm\fR\\d\fIJ\fR\u
- .ce 0
- .sp 1P
- .LP
- .sp 1
- so that \fIS
- \dRNST
- \u\fR can be determined by the approximation:
- \v'6p'
- .sp 1P
- .ce 1000
- \fIS
- \dRNST
- \u\fR \( = \fIS
- \dmeST
- \u\fR + \(*D\fI\fI\d\fIS\fR\\d\fIm\fR\u
- .ce 0
- .sp 1P
- .PP
- .sp 1
- \fINote\ 1\fR \ \(em\ For an explanation of how \(*D\fI\fI\d\fIS\fR\\d\fIm\fR\umay
- be used in
- the determination of Listener Sidetone Rating (LSTR) from Sidetone Masking
- Rating (STMR), see Recommendations\ P.76, P.79 and\ G.111.
- .PP
- \fINote\ 2\fR \ \(em\ In many cases, especially for carbon microphones,
- \(*D\fI\fI\d\fIS\fR\\d\fIm\fR\u
- , and hence also \fIS
- \dRNST
- \u\fR is a function of the level of \fIP\fR\d\fIR\fR\\d\fIN\fR\u. It is
- recommended that in these cases the level of
- \fIP\fR\d\fIR\fR\\d\fIN\fR\ushould be mentioned together with \(*D\fI\fI\d\fIS\fR\\d\fIm\fR\u.
- Typical value of \fIP\fR\d\fIR\fR\\d\fIN\fR\ushould lie within 40\(hy65\
- dBA (see Handbook on Telephonometry,
- \(sc\ 3.3).
- .PP
- \fINote\ 3\fR \ \(em\ Both \fIS\fR\d\fIm\fR\\d\fIJ\fR\uand \fIS
- \dmJ\fR /\fIRN
- \u\fR should use the same techniques, e.g.\ wideband signals measured in
- 1/3\ octave bands.
- .PP
- \fINote\ 4\fR \ \(em\ The approximate formulae for \fIS
- \dRNST
- \u\fR can be deemed to be equal for linear systems.
- .RT
- .ce 1000
- ANNEX\ A
- .ce 0
- .ce 1000
- (to Recommendation P.64)
- .sp 9p
- .RT
- .ce 0
- .ce 1000
- \fBDefinitions of \fR \fBmouth reference point and ear reference point\fR
- .sp 1P
- .RT
- .ce 0
- .PP
- The definitions of mouth reference point (MRP) and ear reference point
- (ERP) are illustrated in Figure\ A\(hy1/P.64.
- .sp 1P
- .RT
- .LP
- .rs
- .sp 20P
- .ad r
- \fBFIGURE\ A\(hy1/P.64, p.\fR
- .sp 1P
- .RT
- .ad b
- .RT
- .LP
- .bp
- .ce 1000
- ANNEX\ B
- .ce 0
- .ce 1000
- (to Recommendation P.64)
- .sp 9p
- .RT
- .ce 0
- .ce 1000
- \fBMeasurement of\fR
- \fBlocal telephone systems\fR \fBcontaining\fR
- .sp 1P
- .RT
- .ce 0
- .ce 1000
- \fBcarbon microphones\fR
- .ce 0
- .PP
- For the measurement of local telephone systems containing carbon microphones,
- various methods have been suggested and tried. The following
- gives, as examples, some of these methods. These same methods can also
- apply to telephones using linear microphones.
- .sp 1P
- .RT
- .PP
- Carbon microphones must be given appropriate conditioning
- treatment at suitable intervals during the measurement (see
- Recommendation\ P.75).
- .PP
- Further information can be found in [3].
- .PP
- \fINote\ 1\fR \ \(em\ The efficiency of the artificial mouth used is not
- generally constant with frequency, so it is necessary, for most of the
- methods described below, to insert appropriate equalization networks between
- the
- electrical signal generator and the loudspeaker of the artificial mouth.
- It is the free field acoustical signal which shall conform to the complex
- signal or the artificial voice specified.
- .PP
- \fINote\ 2\fR \ \(em\ It has been found that for specific applications
- it may be advantageous to use speech levels other than the \(em4.7\ dBPa
- recommended below. This should only be done with care having due regard
- to the particular
- application. Studies carried out during the Study\ Period\ 1985\(hy1988
- have shown that better agreement with subjective test results are obtained
- with somewhat lower levels, e.g.\ over the range \(em4.7\ to \(em7.0\ dBPa.
- .RT
- .PP
- B.1
- The
- \fIupper envelope method\fR has been used in the CCITT Laboratory with
- success for some types of carbon microphone but has been less successful
- with others. The upper envelope method is as follows:
- .sp 9p
- .RT
- .LP
- a)
- Determine the sensitivity as a function of frequency
- at the sound pressure level of \(em4.7\ dB relative to 1\ Pa.
- This is somewhat higher than the mean power of active speech of
- a talker, emitting speech at the vocal level used to determine
- loudness ratings in accordance with the subjective test method
- described in Recommendation\ P.78;
- .LP
- b)
- Repeat a) but with the sound pressure level
- increased by 10\ dB;
- .LP
- c)
- Repeat a) but with the sound pressure level
- decreased by 10\ dB;
- .LP
- d)
- Select from a), b) and c) the highest sensitivity
- at each frequency.
- .sp 1P
- .LP
- B.2
- \fISweeping frequency method\fR
- .sp 9p
- .RT
- .PP
- Some available types of objective instrumentation for
- measuring loudness\(hyrelated ratings use a sweeping frequency covering
- the range from 200\(hy4000\(hy200\ Hz at a periodicity of 1\ sweep per
- second; the instantaneous level within any narrow frequency band varies
- as a function of frequency
- approximately in accordance with the spectrum of speech emitted from the
- human mouth.
- .PP
- This method should not be used for determining \(*D\fI\fI\d\fIS\fR\\d\fIM\fR\u.
- .RT
- .sp 1P
- .LP
- B.3
- \fIPink\(hynoise method\fR
- .sp 9p
- .RT
- .PP
- The handset containing the carbon microphone is placed in front of an artificial
- mouth producing at the MRP pink noise (power spectrum density
- diminishing by 3\ dB/octave) over 1/3rd octave frequency bands centred on the
- preferred frequencies specified in ISO Standard\ 266\(hy1975 at 1/3rd octave
- intervals in the range\ 100 to 8000\ Hz with the band edges conforming to the
- filters described in IEC\ 225.
- .PP
- The total level of the signal, measured over the same bandwidth,
- should be \(em4.7\ dBPa with a tolerance of \(+- | .0\ dB.
- .PP
- \fINote\fR \ \(em\ This may not be practical with all artificial mouths,
- and a narrower bandwidth of 200\ to 8000\ Hz may have to be used for some
- types of
- artificial mouths.
- .PP
- The sensitivity/frequency characteristic is obtained by finding the
- ratio of the spectrum density of the signal delivered by the telephone
- system to the spectrum density of the signal obtained using a small linear
- microphone placed at the MRP under free\(hyfield conditions (after removing
- the
- handset).
- .bp
- .RT
- .sp 1P
- .LP
- B.4
- \fIShaped gaussian noise method\fR
- .sp 9p
- .RT
- .PP
- The method uses shaped Gaussian noise at the MRP whose long\(hyterm
- average spectrum density is the same as shown in Table\ 1/P.50. The total
- level of the signal should be \(em4.7\ dBPa \(+- | \ dB.
- .PP
- The sensitivity/frequency characteristic is obtained as in \(sc\ B.3.
- .RT
- .sp 1P
- .LP
- B.5
- \fIReal\(hyvoice calibration\fR
- .sp 9p
- .RT
- .PP
- This may be performed by measuring speech spectra emitted
- alternately or simultaneously from the carbon microphone under test and a
- calibrated linear microphone. A very small linear microphone can be mounted
- on the telephone being tested. Naturally the most appropriate results
- will be obtained when the talkers are conducting telephone conversations,
- but it is then difficult to have reliable knowledge of the sensitivity/frequency
- characteristic of the linear microphone. It is usually necessary to rely
- upon a suitable artificial mouth to provide the calibration of the linear
- microphone.
- .RT
- .sp 1P
- .LP
- B.6
- \fIApplication of a wideband signal\fR
- .sp 9p
- .RT
- .PP
- The wideband signal is generated by a pseudo\(hyrandom binary sequence
- and is then equalized to have a long\(hyterm average spectrum density flat
- or as defined in Recommendation\ P.50. The output from the carbon microphone
- is then processed by fast Fourier transform (FFT) techniques. This method,
- like the
- previous method, requires calibration by a linear microphone of known
- sensitivity/frequency characteristic to determine the value of\ \fIp\fR\d\fIm\fR\u.
- This method has the advantage that the frequency characteristic may be
- obtained with a sample of test signal of very short duration (e.g.\ 50\
- ms).
- .RT
- .sp 1P
- .LP
- B.7
- \fIMethod using the \fR \fIartificial voice\fR
- .sp 9p
- .RT
- .PP
- The method uses the artificial voice, having spectral and
- time characteristics similar to those of speech.
- .PP
- The sensitivity/frequency characteristic is obtained as in
- \(sc\ B.3 above, but with the artificial mouth supplying the acoustic artificial
- voice, defined in Recommendation\ P.50.
- .RT
- .sp 2P
- .LP
- \fBReferences\fR
- .sp 1P
- .RT
- .LP
- [1]
- CCITT\ \(em\ Question 8/XII, Contribution COM XII\(hyNo.\ 1,
- Study\ Period\ 1989\(hy1992.
- .LP
- [2]
- CCITT\ \(em\ \fIHandbook of Telephonometry\fR ; ITU, Geneva,\ 1987.
- .LP
- [3]
- CCITT\ \(em\ Contribution COM XII\(hyR 27, \(sc\ B.2,
- Study Period\ 1985\(hy1988.
- .sp 2P
- .LP
- \fBRecommendation\ P.65\fR
- .RT
- .sp 2P
- .ce 1000
- \fBOBJECTIVE\ INSTRUMENTATION\ FOR\ THE\ DETERMINATION\fR
- .EF '% Volume\ V\ \(em\ Rec.\ P.65''
- .OF '''Volume\ V\ \(em\ Rec.\ P.65 %'
- .ce 0
- .sp 1P
- .ce 1000
- \fBOF\ LOUDNESS\ RATINGS\fR
- .ce 0
- .sp 1P
- .ce 1000
- \fI(Malaga\(hyTorremolinos, 1984, amended at Melbourne, 1988)\fR
- .sp 9p
- .RT
- .ce 0
- .sp 1P
- .LP
- \fB1\fR \fBIntroduction\fR
- .sp 1P
- .RT
- .PP
- This Recommendation describes the essential features of objective instrumentation
- suitable for the determination of loudness ratings. These
- features are drawn from current Recommendations relating to
- loudness
- ratings
- , the principles of which are defined in Recommendation\ P.76.
- .PP
- It is possible to realize objective instrumentation for loudness
- rating purposes in a number of ways, for example by the assembly of a number
- of separate instruments, each having its own defined function, and possibly
- under some central control, or by means of a dedicated piece of apparatus
- specially designed for the purpose. However, in order to ensure that loudness
- rating
- measurements made in different laboratories have an acceptable level of
- agreement, say \(+- | \ dB, it is essential that the Recommendations relating
- to the measurement of the electro\(hyacoustic performance of telephone
- systems should be followed.
- .bp
- .PP
- The relevant Recommendations are:
- .RT
- .LP
- P.48
- Specification for an intermediate reference system
- .LP
- P.51
- Atificial ear and artificial mouth
- .LP
- P.64
- Determination of sensitivity/frequency characteristics
- of local telephone systems to permit calculation of their
- loundness ratings
- .LP
- P.75
- Standard conditioning method for handsets with carbon
- microphones
- .LP
- P.76
- Determination of loudness ratings; fundamental principles
- .LP
- P.79
- Calculation of loudness ratings
- .FS
- Other algorithms are
- being studied by Study Group\ XII, under
- Question\ 15/XII.
- .FE
- .
- .sp 2P
- .LP
- \fB2\fR \fBInstrumentation\fR
- .sp 1P
- .RT
- .PP
- The four electro\(hyacoustic sections that are required to be included
- in equipment intended for use in determining loudness ratings are described
- below. In each case appropriate calibration is required as a function of
- frequency, and calibration values recorded in the fifth section where the
- particular sensitivity/frequency charac
- teristic is derived and the loudness rating calculated. If the instrumentation
- is to include the measurement of
- listener sidetone rating (LSTR), a sixth section must be provided, namely a
- diffuse room noise source together with appropriate facilities for
- calibration, measurement and analysis in one\(hythird octave bands.
- .PP
- It is necessary to provide certain auxiliary apparatus, such as
- feeding circuits, artificial subscriber cable and exchange terminations, as
- required by the particular Recommendation(s) being followed for any given
- measurement.
- .RT
- .LP
- .sp 1P
- .LP
- 2.1
- \fIArtificial ear\fR
- .sp 9p
- .RT
- .PP
- See \fIa)\fR of Figure 1/P.65.
- .PP
- The artificial ear in the system should be in accordance with
- Recommendation\ P.51 and contain within it a measuring amplifier so that the
- pressure \fIp\fR\d\fIe\fR\uoccurring at the artificial ear cavity can be
- measured as a
- function of frequency, or in frequency bands within the recording and
- measurement system, \fIe)\fR of Figure\ 1/P.65. Means must also be available to
- calibrate the standard microphone used in the artificial ear employing, for
- example, an acoustic calibrator or
- piston\(hyphone
- .
- .RT
- .sp 1P
- .LP
- 2.2
- \fIArtificial voice\fR
- .sp 9p
- .RT
- .PP
- See \fIb)\fR of Figure 1/P.65.
- .PP
- An
- artificial mouth
- complying with Recommendation P.51 must
- be part of the system and be able to produce a prescribed sound field
- at the MRP 25\ mm in front of the lip plane. A signal source will be part
- of the artificial voice and this source may be sine waves (swept or discrete
- .PP
- frequencies) or a wideband signal (e.g.\ the artificial voice defined in
- Recommendation\ P.50, or shaped Gaussian noise as defined in
- Recommendation\ P.64, \(sc\ B.4). Equalization and gain control should
- be part of
- the
- drive system to the artificial mouth
- such that the sound pressure at the MRP can be controlled in accordance
- with the requirements of
- Recommendation\ P.64, \(sc\(sc\ B.1 and\ B.4, or as appropriate.
- .PP
- Calibration of the sound pressure and/or spectrum at the MRP may be
- carried out using the standard microphone used in the artificial ear of
- \(sc\ 2.1 above, making use of the recording and measurement system of
- \(sc\ 2.5 below to
- determine \fIp\fR\d\fIm\fR\uas a function of frequency, or in frequency bands.
- .PP
- Mechanical means must be provided to hold the test handset in the
- LRGP (loudness rating guard\(hyring position), in accordance with the
- requirements of Recommendation\ P.76, Annex\ A. If handsets having carbon
- microphone are being tested, conditioning in accordance with
- Recommendation\ P.75 must be provided.
- .RT
- .sp 1P
- .LP
- 2.3
- \fIElectrical termination\fR
- .sp 9p
- .RT
- .PP
- See \fIc)\fR | f Figure 1/P.65.
- .PP
- The system should contain a 600 ohm balanced terminating impedance
- with means for measuring the terminating voltage, \fIV\fR\d\fIJ\fR\u(see
- Recommendation\ P.64, \(sc\(sc\ 6 and\ 9, as a function of frequency, or
- in frequency
- bands, using the recording and measurement system of \(sc\ 2.5 below. Calibration
- of this section may be carried out using a calibrated voltage
- source.
- .bp
- .RT
- .sp 1P
- .LP
- 2.4
- \fIElectrical signal source\fR
- .sp 9p
- .RT
- .PP
- See \fId)\fR | f Figure 1/P.65.
- .PP
- An electrical signal source must be provided having a 600 ohm balanced
- impedance. The electrical source need not be the same as that used for
- the
- artificial voice but should either be sine waves or a wideband signal. There
- should be means for calibrating and adjusting the generator voltage,
- \fIE\fR\d\fIJ\fR\u, to the requirements of Recommendation P.64, \(sc\(sc\
- 7 and 9 over the frequency range\ 100\(hy8000\ Hz. This may be carried
- out using calibration of the electrical termination of \(sc\ 2.3 above.
- .RT
- .sp 1P
- .LP
- 2.5
- \fIRecording and measurement system\fR
- .sp 9p
- .RT
- .PP
- See \fIe)\fR | f Figure 1/P.65.
- .PP
- In order to determine the sound pressure \fIp\fR\d\fIe\fR\uat the artificial
- ear or the voltage \fIV\fR\d\fIJ\fR\uat the electrical termination it will
- be necessary to
- provide a recording and measurement system. This measurement system may,
- using hardware or software, contain filters in order to improve signal\(hyto\(hynoise
- ratio or for analysing the output of the telephone set in 1/3rd octave
- frequency
- bands. Where a bank of 1/3rd octave filters is used these should be centred
- on the preferred frequencies in accordance with ISO\ 266 and have the
- characteristics in accordance with IEC Publication\ 225.
- .PP
- Within this part of the system there should be recording or storage
- facilities so that calibration and measurement data may be used to derive
- the necessary sensitivity/frequency characteristics in accordance with
- Recommendation\ P.64. The various loudness ratings are then computed in
- accordance with Recommendation\ P.79 from the sensitivity/frequency
- characteristics, taking into account any recognized adjustments, for example
- \fIL\fR\d\fIE\fR\uor \fIL\fR\d\fIM\fR\u. Values for \fIL\fR\d\fIE\fR\uand
- \fIL\fR\d\fIM\fR\umay be fed into the
- calculation using default values (e.g. those listed for \fIL\fR\d\fIE\fR\uin
- Table\ 4/P.79) or from other more appropriate data sources when available.
- .RT
- .LP
- .sp 1P
- .LP
- 2.6
- \fIDiffuse room noise source\fR
- .sp 9p
- .RT
- .PP
- See \fIf\fR \fI)\fR | of Figure 1/P.65.
- .PP
- If LSTR is to be measured, a diffuse room noise source must be
- available, calibrated to provide a prescribed sound field at the position
- to be occupied by the MRP in the absence of the
- test head
- and all other
- obstacles, and as described in Recommendation\ P.64, \(sc\ 9. Calibration
- of the
- diffuse sound pressure \fIp\fR\d\fIR\fR\\d\fIN\fR\umay be carried out using
- the standard
- microphone used in the artificial ear of \(sc\ 2.1, making use of the recording
- and measurement system of \(sc\ 2.5 to determine \fIp\fR\d\fIR\fR\\d\fIN\fR\uas
- a function of frequency in the frequency bands.
- .PP
- Because of the nature of room noise sidetone, it will normally be
- appropriate to use a diffuse sound pressure \fIp\fR\d\fIR\fR\\d\fIN\fR\uthat
- is much lower than the value of \(em4.7\ dBPa used for \fIp\fR\d\fIm\fR\uin
- determining STMR and SLR. Typical
- values for \fIp\fR\d\fIR\fR\\d\fIN\fR\uwould lie in the range 40\(hy65\
- dB SPL (\(em54\ to \(em29\ dBPa,
- A\ weighted), and it should have a frequency spectrum appropriate for the
- application, for example as given in Supplement\ No.\ 13, \(sc\ 2. The
- actual level and type of noise should always be stated in quoting test
- results.
- .RT
- .sp 2P
- .LP
- \fB3\fR \fBMeasurements\fR
- .sp 1P
- .RT
- .PP
- Facilities should be provided to enable the various sections of the instrumentation
- to be connected allowing the measurement of the necessary
- sensitivity/frequency characteristics and calculation of the loudness ratings.
- .PP
- A summary of these interconnections, together with the
- sensitivity/frequency characteristics (SFC) measured for particular loudness
- rating determinations, are given below.
- .RT
- .sp 1P
- .LP
- 3.1
- \fISend loudness rating (SLR)\fR \v'2p'
- .sp 9p
- .RT
- .LP
- Source:
- \fIb)\fR | f Figure 1/P.65
- .LP
- Load:
- \fIc)\fR | f Figure 1/P.65
- .PP
- Send SFC given by:
- \v'6p'
- .sp 1P
- .ce 1000
- \fIS
- \dmJ
- \u\fR = 20 log
- \d10
- \u
- @ { fIV~\dJ\u\fR } over { fIp~\dm\u\fR } @ dB
- .ce 0
- .sp 1P
- .LP
- .sp 1
- .bp
- .LP
- .rs
- .sp 23P
- .ad r
- \fBFigura 1/P.65, p.\fR
- .sp 1P
- .RT
- .ad b
- .RT
- .sp 1P
- .LP
- 3.2
- \fIReceive loudness rating (RLR)\fR \v'2p'
- .sp 9p
- .RT
- .LP
- Source:
- \fId)\fR | f Figure 1/P.65
- .LP
- Load:
- \fIa)\fR | f Figure 1/P.65
- .PP
- Receive SFC given by:
- \v'6p'
- .sp 1P
- .ce 1000
- \fIS
- \dJe
- \u\fR = 20 log
- \d10
- \u
- @ { fIp~\de\u\fR } over { (12~\fIE~\dJ\u\fR } @ dB
- .ce 0
- .sp 1P
- .LP
- .sp 1
- 3.3
- \fISidetone masking rating (STMR)\fR (Talker Sidetone)
- \v'2p'
- .sp 9p
- .RT
- .LP
- Source:
- \fIb)\fR | f Figure 1/P.65
- .LP
- Load:
- \fIa)\fR | f Figure 1/P.65
- .PP
- Sidetone SFC is given by:
- \v'6p'
- .sp 1P
- .ce 1000
- \fIS
- \dmeST
- \u\fR = 20 log
- \d10
- \u
- @ { fIp~\de\u\fR } over { fIp~\dm\u\fR } @ dB
- .ce 0
- .sp 1P
- .LP
- .sp 1
- .PP
- \fINote\fR \ \(em\ The quantity \fIL\fR\d\fIm\fR\\d\fIe\fR\\d\fIS\fR\\d\fIT\fR\uused
- in the calculation of STMR is given by:
- \v'6p'
- .sp 1P
- .ce 1000
- \fIL
- \dmeST
- \u\fR = \(em\fIS
- \dmeST
- \u\fR
- dB
- .ce 0
- .sp 1P
- .LP
- .sp 1
- 3.4
- \fIListener sidetone rating (LSTR)\fR \v'2p'
- .sp 9p
- .RT
- .LP
- Source:
- \fIf\fR \fI)\fR | f Figure 1/P.65
- .LP
- Load:
- \fIa)\fR | f Figure 1/P.65
- .PP
- Room noise sidetone SFC is given by:
- \v'6p'
- .sp 1P
- .ce 1000
- \fIS
- \dRNST
- \u\fR = 20 log
- \d10
- \u
- @ { fIp~\de\u\fR } over { fIp~\dRN~\u\fR } @ dB
- .ce 0
- .sp 1P
- .LP
- .bp
- .sp 1P
- .LP
- 3.5
- \fIOverall loudness rating (OLR) (Overall Send + Receive\fR
- \fI(OSR))\fR \v'2p'
- .sp 9p
- .RT
- .LP
- Source:
- \fIb)\fR | f Figure 1/P.65
- .LP
- Load:
- \fIa)\fR | f Figure 1/P.65
- .PP
- Overall SFC given by:
- \v'6p'
- .sp 1P
- .ce 1000
- \fIS
- \dme
- \u\fR = 20 log
- \d10
- \u
- @ { fIp~\de\u\fR } over { fIp~\dm\u\fR } @ dB
- .ce 0
- .sp 1P
- .LP
- .sp 1
- .sp 1P
- .LP
- 3.6
- \fIJLR Junction loudness rating\fR \v'2p'
- .sp 9p
- .RT
- .LP
- Source:
- \fId)\fR | f Figure 1/P.65
- .LP
- Load:
- \fIc)\fR | f Figure 1/P.65
- .PP
- Junction loss/frequency characteristics given by:
- \v'6p'
- .sp 1P
- .ce 1000
- \fIX
- \dJJ
- \u\fR = 20 log
- \d10
- \u
- @ { (12~\fIE~\dJ\u\fR } over { fIV~\dJ\u\fR } @ dB
- .ce 0
- .sp 1P
- .PP
- .sp 1
- \fINote\fR \ \(em\ Impedance terminations of 600 ohms are assumed.
- \v'2P'
- .sp 2P
- .LP
- \fBRecommendation\ P.66\fR
- .RT
- .sp 2P
- .ce 1000
- \fBMETHODS\ FOR\ EVALUATING\ THE\ \fR \fBTRANSMISSION\ PERFORMANCE\fR
- .EF '% Volume\ V\ \(em\ Rec.\ P.66''
- .OF '''Volume\ V\ \(em\ Rec.\ P.66 %'
- .ce 0
- .sp 1P
- .ce 1000
- \fBOF\ DIGITAL\ TELEPHONE\ SETS\fR
- .FS
- The
- specifications in this Recommendation are subject to future enhancement and
- therefore should be regarded as provisional.
- .FE
- .ce 0
- .sp 1P
- .ce 1000
- \fI(Melbourne, 1988)\fR
- .sp 9p
- .RT
- .ce 0
- .sp 1P
- .LP
- \fB1\fR \fBIntroduction\fR
- .sp 1P
- .RT
- .PP
- The CCITT recommends the following method to evaluate the voice
- transmission performance of a digital telephone set using encoding conforming
- to Recommendation\ G.711 (see also Recommendation\ P.31). A digital telephone
- .PP
- set is one in which the A/D and D/A converters are built in and the connection
- to the network is via a digital bit\(hystream. This poses a fundamental
- problem in applying existing performance and measurement techniques, such
- as
- Recommendations\ P.64, P.34 and\ P.38, since these are generally given
- in terms of a transfer function of analogue input and output quantities,
- e.g.\ a
- frequency response. The principles involved in this Recommendation are
- applicable to handset, headset and hands\(hyfree operation; however, at present
- only procedures applicable to handset operation have been developed.
- .RT
- .sp 2P
- .LP
- \fB2\fR \fBApproaches for\fR
- \fBtesting digital telephones\fR
- .sp 1P
- .RT
- .PP
- There are two methods for evaluating the transmission performance of a
- digital telephone, the codec approach and the direct approach.
- .PP
- In the short term, use of the codec approach is advocated since many Administrations
- already have some experience with this methodology (see
- Recommendation\ O.133).
- .RT
- .LP
- .sp 1
- .bp
- .LP
- .rs
- .sp 13P
- .ad r
- \fBFigure 1/P.66, p.\fR
- .sp 1P
- .RT
- .ad b
- .RT
- .sp 1P
- .LP
- 2.1
- \fICodec approach\fR
- .sp 9p
- .RT
- .PP
- In this approach, shown in Figure 1/P.66, a codec is used to
- convert the companded digital input/output bit\(hystream of the telephone
- set to the equivalent analogue values, so that existing test procedures
- and equipment can be used. This codec should be a high\(hyquality codec
- whose characteristics
- are as close as possible to ideal
- (see\ \(sc\ 5).
- .RT
- .sp 1P
- .LP
- 2.2
- \fIDirect digital processing approach\fR
- .sp 9p
- .RT
- .PP
- In this approach, shown in Figure 2/P.66, the companded digital
- input/output bit\(hystream of the telephone set is operated upon directly.
- .PP
- \fINote\fR \ \(em\ This approach is still under study in Question 38/XII.
- .RT
- .LP
- .rs
- .sp 12P
- .ad r
- \fBFigure 2/P.66, p.\fR
- .sp 1P
- .RT
- .ad b
- .RT
- .sp 2P
- .LP
- \fB3\fR \fBDefinition of 0 dB reference point\fR
- .sp 1P
- .RT
- .PP
- To preserve compatibility with existing codecs already in use in
- local digital switches, which are defined as a 0\ dBr point, the codec
- (A\(hy\ or
- \(*m\(hylaw) sould be defined as follows:
- .RT
- .LP
- \(em
- D/A converter: a digital test sequence (DTS) representing the PCM equivalent
- of an analogue sinusoidal signal whose r.m.s. value is
- 3.14\ dB (A\(hylaw) or 3.17\ dB (\(*m\(hylaw) below the maximum full\(hyloaded
- capacity of
- the codec will generate 0\ dBm across a 600\ ohm load;
- .LP
- \(em
- A/D converter: a 0 dBm signal generated from a 600 ohm source will give
- the digital test sequence (DTS) representing the PCM equivalent of an analogue
- sinusoidal signal whose r.m.s. value is 3.14\ dB (A\(hylaw) or 3.17\ dB
- (\(*m\(hylaw) below the maximum full load capacity of the codec;
- .LP
- where DTS is defined as a periodic sequence of character
- signals as given in Tables\ 5/G.711 and\ 6/G.711.
- .bp
- .sp 2P
- .LP
- \fB4\fR \fBDefinition of interfaces\fR
- .sp 1P
- .RT
- .PP
- The digital telephone test equipment will, in general, be connected to
- the telephone under test through an interface.
- .PP
- Such an interface should be able to provide all the signalling and
- supervisory sequences necessary for the telephone set to be working in
- all test modes. The interface must be capable of converting the digital
- output stream
- from the tested set (which may be in various formats, depending on the
- specific type of telephone set, e.g.\ conforming to Recommendation\ I.412
- for ISDN sets), to a form compatible with the test equipment. Interfaces
- can be applied for
- sending and receiving separately, taking into account telephone sets which
- are connected to various types of exchanges.
- .RT
- .sp 2P
- .LP
- \fB5\fR \fBCodec specification\fR
- .sp 1P
- .RT
- .sp 1P
- .LP
- 5.1
- \fIIdeal codec\fR
- .sp 9p
- .RT
- .PP
- This characteristic can be realized, for example, using oversampling techniques
- and digital filters.
- .FE
- The ideal codec consists of an independent encoder and decoder
- whose characteristics are hypothetical and comply with Recommendation\ G.711.
- The ideal encoder is a perfect analogue\(hyto\(hydigital converter preceded
- by an
- ideal low\(hypass filter (assumed to have no attenuation/frequency distortion
- and no envelope\(hydelay distortion), and may be simulated by a digital
- processor.
- The ideal decoder is a perfect digital\(hyto\(hyanalogue converter followed
- by an ideal low\(hypass filter (assumed to have no attenuation/frequency
- distortion and no envelope\(hydelay distortion), and which may be simulated
- by a digital processor
- .
- .PP
- For the measurement of the sending side of a telephone set, the output
- digital signal is converted by the decoder to an analogue signal. The
- electrical characteristics of this output signal are measured using
- conventional analogue instruments. For the measurement of the receiving
- side of a telephone set, the analogue output from a signal source is converted
- to a
- digital signal by the ideal encoder and fed to the receiving input of the
- digital telephone set.
- .RT
- .sp 1P
- .LP
- 5.2
- \fIReference codec\fR
- .sp 9p
- .RT
- .PP
- A practical implementation of an ideal codec may be called a
- reference codec (see Recommendation\ O.133, \(sc\ 4).
- .PP
- For the reference codec, characteristics such as attenuation/frequency
- distortion, idle channel noise, quantizing distortion,\ etc. should be
- better
- than the requirements specified in Recommendation\ G.714, so as not to
- mask the corresponding parameters of the set under test. A suitable reference
- codec may be realized by using:
- .RT
- .LP
- 1)
- at least 14 bit linear A/D and D/A converters of high
- quality, and transcoding the output signal to the A\(hy or \(*m\(hylaw
- PCM format;
- .LP
- 2)
- a filter response that meets the requirements of
- Figure\ 3/P.66.
- .sp 1P
- .LP
- 5.2.1
- \fIAnalogue interface\fR
- .sp 9p
- .RT
- .PP
- The output and input impedances return loss and longitudinal
- conversion losses of the analogue interface of the reference codec should
- be in accordance with Recommendation\ O.133, \(sc\ 3.1.1.
- .RT
- .sp 1P
- .LP
- 5.2.2
- \fIDigital interface\fR
- .sp 9p
- .RT
- .PP
- The fundamental requirements for the reference codec digital
- interface are given in the appropriate Recommendations (e.g.\ I.430\(hySeries
- Recommendations for ISDN telephone sets).
- .RT
- .sp 2P
- .LP
- \fB6\fR \fBMeasurement of digital telephone transmission characteristics\fR
- .sp 1P
- .RT
- .PP
- Use of the codec test approach means that test procedures for
- digital telephone sets in general follow those for analogue sets (see
- Recommendation\ P.64). The reference codec should meet the requirements
- of \(sc\ 5. An important difference, however, concerns the test circuits
- themselves, see
- Figures\ 4/P.66 to\ 10/P.66.
- .PP
- The set is connected to the interface and is placed in the active call state.
- .PP
- \fINote\fR \ \(em\ When measuring digital telephone sets, it is advisable to
- avoid measuring at sub\(hymultiples of the sampling frequency. There is a
- tolerance on the frequencies of \(+- | % which may be used to avoid this
- problem, except for 4\ kHz where only the \(em2%\ tolerance may be used.
- .bp
- .RT
- .LP
- .rs
- .sp 20P
- .ad r
- \fBFigure 3/P.66, p.\fR
- .sp 1P
- .RT
- .ad b
- .RT
- .sp 2P
- .LP
- 6.1
- \fISending\fR
- .sp 1P
- .RT
- .sp 1P
- .LP
- 6.1.1
- \fISending frequency characteristic\fR
- .sp 9p
- .RT
- .PP
- The sending frequency characteristic is measured according to
- Recommendation\ P.64 using the measurement set\(hyup shown in Figures\ 4/P.66
- or\ 5/P.66, depending on the excitation signal used.
- .RT
- .LP
- .rs
- .sp 18P
- .ad r
- \fBFigure 4/P.66, p.\fR
- .sp 1P
- .RT
- .ad b
- .RT
- .LP
- .bp
- .LP
- .rs
- .sp 18P
- .ad r
- \fBFigure 5/P.66, p.\fR
- .sp 1P
- .RT
- .ad b
- .RT
- .sp 1P
- .LP
- 6.1.2
- \fISend loudness rating\fR
- .sp 9p
- .RT
- .PP
- This should be calculated from the sensitivity/frequency
- characteristic determined in \(sc\ 6.1.1 by means of Recommendation\ P.79.
- .PP
- \fINote\fR \ \(em\ Other methods for calculating loudness ratings used
- by some Administrations for their own internal planning purposes can be
- found in
- Supplement\ No.\ 19.
- .RT
- .sp 1P
- .LP
- 6.1.3
- \fIDistortion\fR
- .sp 9p
- .RT
- .PP
- Under study in Question 38/XII, but a method used by several
- European Administrations can be found in\ [1].
- .RT
- .sp 1P
- .LP
- 6.1.4
- \fINoise\fR
- .sp 9p
- .RT
- .PP
- Under study in Question 38/XII, but a method used by several
- European Administrations can be found in\ [1].
- .RT
- .sp 1P
- .LP
- 6.1.5
- \fILinearity\fR
- .sp 9p
- .RT
- .PP
- Under study in Question 38/XII, but a method used by several
- European Administrations can be found in\ [1].
- .RT
- .sp 1P
- .LP
- 6.1.6
- \fIDiscrimination against out\(hyof\(hyband input signal\fR
- .sp 9p
- .RT
- .PP
- Under study in Question 38/XII, but a method used by several
- European Administrations can be found in\ [1].
- .RT
- .sp 2P
- .LP
- 6.2
- \fIReceiving\fR
- .sp 1P
- .RT
- .sp 1P
- .LP
- 6.2.1
- \fIReceiving frequency characteristic\fR
- .sp 9p
- .RT
- .PP
- The receiving frequency characteristic is measured according to
- Recommendation\ P.64 using the measurement set\(hyup shown in Figures\ 6/P.66
- or\ 7/P.66, depending on the excitation signal used.
- .bp
- .RT
- .LP
- .rs
- .sp 13P
- .ad r
- \fBFigure 6/P.66, p.\fR
- .sp 1P
- .RT
- .ad b
- .RT
- .LP
- .rs
- .sp 14P
- .ad r
- \fBFigure 7/P.66, p.\fR
- .sp 1P
- .RT
- .ad b
- .RT
- .sp 1P
- .LP
- 6.2.2
- \fIReceiving loudness rating\fR
- .sp 9p
- .RT
- .PP
- This should be calculated from the sensitivity/frequency
- characteristic determined in \(sc\ 6.2.1 by means of Recommendation\ P.79.
- .PP
- \fINote\fR \ \(em\ Other methods for calculating loudness rating used by some
- Administrations for their own internal planning purposes can be found in
- Supplement\ No.\ 19.
- .RT
- .sp 1P
- .LP
- 6.2.3
- \fIDistortion\fR
- .sp 9p
- .RT
- .PP
- Under study in Question 38/XII, but a method used by several
- European Administrations can be found in\ [1].
- .RT
- .sp 1P
- .LP
- 6.2.4
- \fINoise\fR
- .sp 9p
- .RT
- .PP
- Under study in Question 38/XII, but a method used by several
- European Administrations can be found in\ [1].
- .RT
- .sp 1P
- .LP
- 6.2.5
- \fILinearity\fR
- .sp 9p
- .RT
- .PP
- Under study in Question 38/XII, but a method used by several
- European Administrations can be found in\ [1].
- .bp
- .RT
- .sp 1P
- .LP
- 6.2.6
- \fISupurious out\(hyof\(hyband signals\fR
- .sp 9p
- .RT
- .PP
- Under study in Question 38/XII, but a method used by several
- European Administrations can be found in\ [1].
- .RT
- .sp 1P
- .LP
- 6.3
- \fISidetone\fR
- .sp 9p
- .RT
- .PP
- Provision should be made for driving the microphone of the
- telephone set under test as described in \(sc\ 6.1 and measuring the receiver
- output as described in \(sc\ 6.2. The recommended method of measuring sidetone
- is with the microphone and receiver mounted in the same handset, and using
- a test fixture which includes the artificial mouth and the artificial ear
- located
- relative to each other in accordance with Recommendation\ P.64.
- .PP
- \fINote\fR \ \(em\ Care should be taken to avoid mechanical coupling between
- the artificial mouth and the artificial ear.
- .RT
- .sp 2P
- .LP
- 6.3.1
- \fISidetone frequency characteristic\fR
- .sp 1P
- .RT
- .sp 1P
- .LP
- 6.3.1.1
- \fITalker sidetone frequency characteristic\fR
- .sp 9p
- .RT
- .PP
- The talker sidetone frequency characteristic is measured according to Recommendation\
- P.64 using the measurement set\(hyup of Figures\ 8/P.66 or\ 9/P.66 depending
- on the excitation signal used.
- .RT
- .LP
- .rs
- .sp 14P
- .ad r
- \fBFigure 8/P.66, p.\fR
- .sp 1P
- .RT
- .ad b
- .RT
- .LP
- .rs
- .sp 15P
- .ad r
- \fBFigure 9/P.66, p.\fR
- .sp 1P
- .RT
- .ad b
- .RT
- .LP
- .bp
- .sp 1P
- .LP
- 6.3.1.2
- \fIListener sidetone frequency characteristic\fR
- .sp 9p
- .RT
- .PP
- The listener sidetone frequency characteristic is measured
- according to Recommendation\ P.64 using the measurement set\(hyup of
- Figure\ 10/P.66.
- .RT
- .LP
- .rs
- .sp 17P
- .ad r
- \fBFigure 10/P.66, p.\fR
- .sp 1P
- .RT
- .ad b
- .RT
- .sp 1P
- .LP
- 6.3.2
- \fISidetone masking rating\fR
- .sp 9p
- .RT
- .PP
- This should be calculated from the sensitivity/frequency
- characteristic determined in \(sc\ 6.3.1.2 by means of Recommendation\ P.79.
- .RT
- .sp 1P
- .LP
- 6.3.3
- \fIListener sidetone rating\fR
- .sp 9p
- .RT
- .PP
- This should be calculated from the sensitivity/frequency
- characteristic determined in \(sc\ 6.3.1.2 by means of Recommendation\ P.79.
- .RT
- .sp 1P
- .LP
- 6.4
- \fIEcho return loss\fR
- .sp 9p
- .RT
- .PP
- Under study in Question 38/XII, but a method used by several
- European Administrations can be found in\ [1].
- .RT
- .sp 1P
- .LP
- 6.5
- \fIDelay\fR
- .sp 9p
- .RT
- .PP
- Under study in Question 38/XII, but a method used by several
- European Administrations can be found in\ [1].
- .RT
- .sp 2P
- .LP
- \fBReferences\fR
- .sp 1P
- .RT
- .LP
- [1]
- CCITT\ \(em\ Contribution COM XII\(hyNo.179, \fITransmission aspects
- for digital\fR \fItelephony\fR (Norway), Study Period\ 1985\(hy1988.
- .LP
- .rs
- .sp 5P
- .ad r
- Blanc
- .ad b
- .RT
- .LP
- .bp
-