1、INTERNATIONAL TELECOMMUNICATION UNION ITU=T TELECOM M U N I CATI ON STANDARDIZATION SECTOR OF ITU P.51 (08196) SERIES P: TELEPHONE TRANSMISSION QUALITY Objective measuring apparatus Artificial Mouth TU-T Recommendation P.51 (Previously ?CCITT Recommendation?) ITU-T P-SERIES RECOMMENDATIONS TELEPHONE
2、 TRANSMISSION QUALITY Vocabulary and effects of transmission parameters on customer opinion of transmission qualiy P. 10-P.29 Subscribers lines and sets P.300-P.399 Subscribers lines and sets P.30-P.39 Transmission standards P.40-P.49 Objective measuring apparatus P.500-P.599 - - Objective measuring
3、 apparatus P.50-P.59 Objective electro-acoustical measurements P.60-P.69 Measurements related to speech loudness Methods for objective and subjective assessment of quality P.70-P.79 P.800-P.999 Methods for objective and subjective assessment of quality P.80-P.99 For further details, please refer to
4、ITU-T List of Recommendations. FOREWORD The -T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (IT). The IT-T is responsible for studying technical, operating and tariff questions and issuing Recommen- dations on them with a view to standa
5、rdizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommndations on these topics. The approval of Recommendations by th
6、e Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). ITU-T Recommendation P.51, was revised by ITU-T Study Group 12 (1993-1996) and was approved under the WTSC Resolution No. 1 procedure on the 30th of August 1996. NOTE In this Recommend
7、ation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. O ITU 1997 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, inclu
8、ding photocopying and microfilm, without permission in writing from the ITU. Recommendation P.51 (08/96) i CONTENTS 1 Scope 2 Normative references . 3 Object . Acoustic characteristics of the artificial mouth 5.1 Nonnalised free-field response . : . 5.2 Normalised obstacle diffraction 5.3 Maximum de
9、liverable sound pressure level . 5.4 Distortion 5.5 Linearity 6 Miscellaneous . 6.1 Delivery conditions . 6.3 Stray magnetic field Declaration of model type . 4 Definitions 5 6.2 Stability . 6.4 Page 1 1 1 1 2 2 5 6 6 6 6 6 7 7 7 11 Recommendation P.51 (08/96) - STDOITU-T RECMN P.51i-ENGL 199b LiBb2
10、591 Clb2Li058 b27 SUMMARY The Recommendation specifies the acoustical and electrical characteristics of the Artificial Mouth used for telephonometric measurements. The sound radiation patterns are specified at a number of points in front of the mouth, as well as the sound difiaction characteristics
11、occurring by inserting a reference obstacle in the sound field generated by the mouth. Also the dynamic range of the generated sound is specified, as well as the linearity characteristics of the device. The proposed revision of this Recommendation affects the latter aspects, namely the distortion an
12、d output linearity requirements of the Artificial Mouth. . Recommendation P.51 (08/96) 111 Recommendation P.51 ARTIFICIAL MOUTH (Helsinki, 1993; revised in 1996) 1 Scope This Recommendation specifies the artificial mouth for telephonometric use. The methods of use of the artificial mouth are outside
13、 the scope of this Recommendation. 2 Normative references The following Recommendations, and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and
14、 other references are subject to revision; all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid IT-T Recommendations is regularly published.
15、 - ITU-T Recommendation P.50 (1993), ArtiJicial voices. - ITU-T Recommendation P.64 (1993), Determination of sensitivity/fiequency characteristics of local telephone systems. - CCITT Recommendation O. 13 1 (1988), Quantizing distortion measuring equipment using a pseudo-random noise test signal. 3 O
16、bject The artificial mouth is a device that approximates the acoustic field generated by the human mouth in the near field. It is used for measuring objectively the sending characteristics of handset-equipped telephone sets as specified in Recommendation P.64. It may also be used for measuring the s
17、ending characteristics of loudspeaking telephones at distances up to 0.5 m from the lip plane, but the accuracy with which it reproduces the sound field is slightly reduced. 4 Definitions For the purposes of this Recommendation, the following definitions apply: 4.1 radiation pattern similar to those
18、 of the average human mouth. artificial mouth: A device consisting of a loudspeaker mounted in an enclosure and having a directiviw and 4.2 lip ring: Circular ring of thin rigid rod, having a diameter of 25 mm and less than 2 mm thick. It shall be constructed of non-magnetic material and be solidly
19、fixed to the case of the artificial mouth. The lip ring defines both the reference axis of the mouth and the mouth reference point. 4.3 orifice. lip plane: Outer plane of the lip ring. The lip plane is normally different fiom the plane of the mouth simulator 4.4 reference axis: The line perpendicula
20、r to the lip plane containing the centre of the lip ring. 4.5 It shall be vertically oriented in order to reproduce the acoustic field generated by a person in the upright position. vertical plane: A plane containing the reference axis that divides the artificial mouth into symmetrical halves. 4.6 h
21、orizontally oriented in order to reproduce the acoustic field generated by a person in the upright position. horizontal plane: The plane containing the reference axis, perpendicular to the vertical plane. It shall be 4.7 mouth reference point (MRP): The point on the reference axis, 25 mm in front of
22、 the lip plane. Recommendation P.51 (08/96) 1 4.8 normalised free-field response: Difference in dB between the third-octave spectrum level of the signal delivered by the artificial mouth at a given point in the free field kd the third-octave spectrum level of the signal delivered simultaneously at t
23、he MRP. The characteristic is measured by generating the artificial voice (see Recommendation P.50) a speech-shaped random noise, a pink noise, or other adequate wideband signals. On-axis displacement from the lip plane (mm) 12.5 50 1 O0 140 4.9 reference obstacle: Disc constructed of hard, stable a
24、nd non-magnetic material, such as brass, having a diameter of 63 mm and 5 mm thick. In order to measure the normalised obstacle dimaction of the mouth simulator, it shall be fitted with a ?4 inch pressure microphone, mounted at the centre with the diaphragm flush with the disc surface facing the art
25、ificial mouth. Off-axis; perpendicular displacement (mm) O O O O 4.10 normalised obstacle diffraction: Difference in dB between the third-octave spectrum level of the acoustic pressure delivered by the artificial mouth at the surface of the reference obstacle and the third-octave spectrum level of t
26、he pressure simultaneously delivered at the point on the reference axis, 500 mm in front of the lip plane. The characteristic is defined for positions of the reference obstacle in front of the artificial mouth, with the disc axis coinciding with the reference axis, and is measured by generating the
27、artificial voice (see Recommendation PSO), a speech-shaped random noise, a pink noise, or other adequate wideband signais. 4.11 artificial voice: A mathematically defined signal which reproduces human speech characteristics, relevant to the characterisation of linear and non-linear telecommunication
28、 systems. It is intended to give a satisfactory correlation between objective measurements and tests with real speech. 4.12 or other electric devices. electrical artificial voice: The artificial voice produced as an electric signal, for testing transmission channels 4.13 complies with the same time
29、and spectral specifications as the electrical artificial voice. acoustic artificial voice: Acoustic signal at the MRP (Mouth Reference Point) of the artificial mouth. It 5 Acoustic characteristics of the artificial mouth 5.1 Normalised free-field response The normalised free-field response is specif
30、ied at 17 points: ten in the near field and seven in the far field. Near-field points are listed in Table 1, while far-field points are listed in Table 2. NOTE - It shall be noticed that points in Table 2 lie on a plane parallel to the lip plane. TABLE 1P.51 Coordinates of points in the near field M
31、easurement point 1 2 3 4 5 6 7 8 9 10 O O 25 25 25 25 20 horizontal 40 horizontal 20 horizontal 40 horizontal 20 vertical (downwards) 40 vertical 2 Recommendation P.51 (08/96) - STDmITU-T RECMN P-51-ENGL 177b m 4b2571 Ob24Dbl 113 D Distance from the lip plane (mm) TABLE 2P.51 Coordinates of points i
32、n the far field Azimuth angle Elevation angle (horizontal) (vertical) (degree) (degree) Measurement point 11 12 13 14 15 16 17 500 500 500 500 500 500 500 O O O +IS O +3 O O -15 O -3 O 15 O 30 O Table 3 provides the normalised free-field response of the artificial mouth, together with tolerances, fo
33、r the bandwidth between 100 Hz and 8 kHz. The requirements at each point not lying in the vertical plane shall also be met by the correspondent point in the symmetrical half-space. The characteristic shall be checked by using appropriate microphones, as specified in Table 4. Pressure microphones sha
34、ll be oriented with their axes perpendicular to the sound direction, while free-field microphones shall be oriented with their axes parallel to the direction of sound. If a compressor microphone is used with the artificial mouth, it (or an equivalent dummy) shall be left in place while checking the
35、normalised free-field response. Frequency (Ha 1 O0 125 160 200 250 315 400 500 63 O 800 1 O00 I250 1600 2000 2500 3150 4000 5000 6300 8000 TABLE 3aIP.51 Normalised free-field response on axis in the near field Measurement point 4.2 4.2 4.2 4.0 4.0 4.0 4.0 4.1 4.2 4.2 4.1 3.9 3.8 3.6 3.5 3.6 3.7 3.7
36、3.8 3.8 2 (dB) -5.0 -5.0 -5.0 -5.0 -5.0 -5.0 -5.0 -5.0 -4.9 -4.8 -4.8 -4.8 -4.8 -4.7 -4.6 -4.6 -4.6 -4.5 -4.5 -4.9 3 (dB) -11.0 -10.9 -10.7 -10.7 -10.6 -10.6 -10.6 -10.6 -10.5 -10.5 -10.4 -10.2 -10.0 -10.0 -9.4 -9.4 -9.7 -9.7 -9.7 -10.0 -13.6 -13.6 -13.6 -13.3 -13.2 -13.2 -13.2 -13.2 -13.4 -13.4 -12
37、.9 -12.7 -12.7 -12.7 -12.3 -12.0 -12.3 -12.6 -12.6 -12.7 Tolerance (dB) fl.5 111.5 fl.5 fl.5 fl.5 -1.5/+1 -1.5/+1 -1.5/+1 - 1.5/+1 51.0 fl.O +1 .o +I .o 51.0 I1.0 fl.O f1.5 +I .5 -1.5/+2 -1.5/+2 .l Recommendation PSI (08/96) 3 TABLE 3bP.51 Normalised free-field response off axis in the near field I
38、a) The measurements on the human mouth at point 5 are quite scattered, so the response at this point is only indicatively provided and no tolerance apply. I TABLE 3cR.51 Normalised free-field response in the far field , Frequency range (100 HZ - 8 Hz) Measurement point I Tolerance I (dB) I (dB) Resp
39、onse 11 12 13 14 15 16 17 -24.0 -24.0 -25.0 -24.0 -25.0 -24.0 -25.0 -314 -314 t 3.0 -3/+4 t 3.0 -3/+4 f 3.0 4 Recommendation P.51 (08/96) Measurement point 1,2,5,6,7,8,9, 10 3,4 11, 12, 13, 14, 15, 16, 17 MRP 5.2 Normalised obstacle diffraction The normalised obstacle diffraction of the artificial m
40、outh is defined at three points on the references axis, as specified in Table 5. If a compressor microphone is used with the artificial mouth, it (or an equivalent dummy) shall be left in place while checking the normaliced obstacle diffraction. Microphone size (maximum) Microphone equalisation (inc
41、h) 1 14 Pressure 112 Pressure 1 Freelfield i 14 Pressure Frequency 250 315 400 500 630 800 1 O00 1250 1600 2000 2500 3150 4000 5000 6300 8000 TABLE 5P.51 Normalised obstacle diffraction Measurement point 34.2 34.0 34.0 33.2 33.2 33.9 33.8 33.3 33.0 32.1 31.3 31.0 30.9 30.6 31.0 31.0 31.6 33.2 33.7 3
42、2.0 a) Only indicative values - tolerances not specified. 28.5 28.5 28.8 28.0 28.0 28.5 28.5 27.9 27.5 26.6 25.9 25.8 26.0 26.7 27.8 28.0 28.8 28.4 27.5 24.5 20 (50 mm) (dB) 23.2 22.9 22.9 22.1 22.0 22.5 22.4 21.9 21.5 20.9 20.3 20.3 21.1 22.0 24.7 24 .O 24.3 23.9 24.0 19.5 +3/-2 +3/-2 +3/-2 +3/-2 +
43、3/-2 - 1 /+2.5 - 1 /+2.5 - 1 /+2.5 -1/+2.5 -1/+2.5 -11+2.5 -1/+2.5 -1/+2.5 -1/+2.5 -1/+2.5 -11t2.5 a) 4 a) a) Recommendation P.51 (08/96) 5 5.3 Maximum deliverable sound pressure level 100 HZ - 125 Hz The artificial mouth shall be able to deliver steadily the acoustic artificial voice at sound press
44、ure levels up to at least +6 dBPa at the MRF. 2nd harmonic 3nd harmonic 10% 10% 5.4 Distortion 125 HZ - 200 HZ 200 HZ - 8 kHZ 5.4.1 Harmonic distortion 4% 4% 1% 1% When delivering sine tones, with amplitudes up to +6 dBPa at the MRP, the harmonic distortion of the acoustic signal (delivered at the M
45、RP) shall comply with the limits specified in Table 6. TABLE 6P.51 Maximum harmonic distortion of the artificial mouth Additionally to the requirement of Table 6, when delivering sine tones with frequencies between 1004 Hz and 1025 Hz with a level up to 10 dBPa the total harmonic distortion (2nd and
46、 3rd harmonics) of the artificial mouth measured at the MRP shall not exceed 1.5%. 5.4.2 Total distortion When delivering noise signals according to Recommendation 0.131 with levels up to +5 dBPa at the MRP, the total distortion of the artificial mouth measured at the MRE shall not exceed 1.5%. 5.5
47、Linearity Positive or negative variation of 6 dB of the feeding electrical signal shall produce corresponding variations of 6 dB f 0.5 dB at the MRP for output pressures in the range fiom -14 dBPa to +6 &Pa. This requirement shall be met both for complex excitations, such as the artificial voice, an
48、d for sinusoidal excitations in the range fiom 100 Hz to 8 kHz. NOTE -Better and less temperature dependent linearity performances can be achieved by controlling the electrical excitation current instead of the feeding voltage. For applications requiring better performances than here specified and e
49、xtended dynamic ranges, it is recommended to individually calibrate the artificial mouth used and to compensate the measured data by taking into account the calibration results. An effective alternative technique also consists in monitoring the generated acoustic pressure by means of a measurement microphone placed at the acoustic outlet of the artificial mouth. 6 Miscellaneous 6.1 Delivery conditions The artificial mouth shall be delivered by the manufacturer with the mechanical fixtures required to place the % inch calibration microphone at the MRP, as speci
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