1、 International Telecommunication Union ITU-T P.342TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (06/2009) SERIES P: TERMINALS AND SUBJECTIVE AND OBJECTIVE ASSESSMENT METHODS Voice terminal characteristics Transmission characteristics for narrow-band digital loudspeaking and hands-free telephony te
2、rminals Recommendation ITU-T P.342 ITU-T P-SERIES RECOMMENDATIONS TERMINALS AND SUBJECTIVE AND OBJECTIVE ASSESSMENT METHODS Vocabulary and effects of transmission parameters on customer opinion of transmission quality Series P.10 Voice terminal characteristics Series P.30 P.300 Reference systems Ser
3、ies P.40 Objective measuring apparatus Series P.50 P.500 Objective electro-acoustical measurements Series P.60 Measurements related to speech loudness Series P.70 Methods for objective and subjective assessment of speech quality Series P.80 P.800Audiovisual quality in multimedia services Series P.90
4、0 Transmission performance and QoS aspects of IP end-points Series P.1000 Communications involving vehicles Series P.1100 For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T P.342 (06/2009) i Recommendation ITU-T P.342 Transmission characteristics for narrow-band digit
5、al loudspeaking and hands-free telephony terminals Summary Recommendation ITU-T P.342 provides audio performance requirements for digital hands-free and loudspeaking telephony terminals using, in the telephone band (300-3400 Hz), the waveform encoding according to Recommendations ITU-T G.711 (PCM at
6、 both 64 kbit/s and 56 kbit/s) and ITU-T G.726 (ADPCM 32 kbit/s). This Recommendation does not deal with audio performance requirements for digital telephones using coding schemes other than waveform encoding and at bit rates lower than 32 kbit/s. Source Recommendation ITU-T P.342 was approved on 22
7、 June 2009 by ITU-T Study Group 12 (2009-2012) under Recommendation ITU-T A.8 procedures. ii Rec. ITU-T P.342 (06/2009) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (IC
8、Ts). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication
9、 Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of infor
10、mation technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agen
11、cy. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some
12、other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or im
13、plementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development proc
14、ess. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongl
15、y urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2010 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T P.342 (06/2009) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Defi
16、nitions and abbreviations. 2 3.1 Definitions 2 3.2 Abbreviations . 2 4 Test configuration. 3 4.1 Electrical interface specifications. 3 4.2 Test arrangement 3 4.3 Test conditions 6 4.4 Test signals . 8 4.5 Test signal levels 9 4.6 Accuracy of calibrations. 10 5 Technical requirements. 10 5.1 Sending
17、 characteristics . 10 5.2 Receiving characteristics 14 5.3 Echo path loss characteristics. 19 5.4 Delay. 20 Rec. ITU-T P.342 (06/2009) 1 Recommendation ITU-T P.342 Transmission characteristics for narrow-band digital loudspeaking and hands-free telephony terminals 1 Scope This Recommendation provide
18、s audio performance requirements for hands-free and loudspeaking telephones using, in the telephone narrow-band (300-3400 Hz), the waveform encoding according to ITU-T G.711 (PCM at both 64 kbit/s and 56 kbit/s) and ITU-T G.726 (ADPCM 32 kbit/s). Audio performance requirements for headset terminals
19、are included in ITU-T P.310. IP terminals are not included in this Recommendation. Audio performance requirements for digital telephones using coding schemes other than waveform encoding and at bit rates lower than 32 kbit/s are under study. 2 References The following ITU-T Recommendations and other
20、 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 other references are subject to revision; users of this Recommendation are therefore encouraged t
21、o investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document,
22、the status of a Recommendation. ITU-T G.122 Recommendation ITU-T G.122 (1993), Influence of national systems on stability and talker echo in international connections. ITU-T G.131 Recommendation ITU-T G.131 (1996), Control of talker echo. ITU-T G.223 Recommendation ITU-T G.223 (1988), Assumptions fo
23、r the calculation of noise on hypothetical reference circuits for telephony. ITU-T G.711 Recommendation ITU-T G.711 (1988), Pulse Code Modulation (PCM) of voice frequencies. ITU-T G.726 Recommendation ITU-T G.726 (1990), 40, 32, 24, 16 kbit/s Adaptive Differential Pulse Code Modulation (ADPCM). ITU-
24、T O.41 Recommendation ITU-T O.41 (1994), Psophometer for use on telephone-type circuits. ITU-T P.51 Recommendation ITU-T P.51 (1996), Artificial mouth. ITU-T P.57 Recommendation ITU-T P.57 (2005), Artificial ears. ITU-T P.58 Recommendation ITU-T P.58 (1996), Head and torso simulator for telephonomet
25、ry. ITU-T P.64 Recommendation ITU-T P.64 (2007), Determination of sensitivity/frequency characteristics of local telephone systems. ITU-T P.79 Recommendation ITU-T P.79 (2007), Calculation of loudness ratings for telephone sets. ITU-T P.310 Recommendation ITU-T P.310 (2003), Transmission characteris
26、tics for telephone-band (300-3400 Hz) digital telephones. 2 Rec. ITU-T P.342 (06/2009) ITU-T P.340 Recommendation ITU-T P.340 (2000), Transmission characteristics and speech quality parameters of hands-free terminals. ITU-T P.501 Recommendation ITU-T P.501 (2000), Test signals for use in telephonome
27、try. ITU-T P.581 Recommendation ITU-T P.581 (2000), Use of head and torso simulator (HATS) for hands-free terminal testing. ISO 266 ISO 266:1997, Acoustics Preferred frequencies. IEC 61672-1 IEC 61672-1:2002, Electroacoustics Sound level meters Part 1: Specifications. 3 Definitions and abbreviations
28、 3.1 Definitions This Recommendation defines the following terms: 3.1.1 double talk: An operation mode, where two users are speaking simultaneously. 3.1.2 ear-drum reference point (DRP): A point located at the end of the ear canal, corresponding to the ear-drum position. 3.1.3 ear reference point (E
29、RP): A virtual point for geometric reference located at the entrance to the listeners ear, traditionally used for calculating telephonometric loudness ratings. 3.1.4 group-audio terminal: A speakerphone set primarily designed for use by several users, which will not be equipped with a handset. 3.1.5
30、 hands-free reference point (HFRP): A point located on the axis of the artificial mouth, at 50 cm from the lip ring, where the level calibration is made in free field. It corresponds to the measurement point 11, as defined in ITU-T P.51. 3.1.6 hands-free terminal (HFT): A telephone set that does not
31、 require the use of hands during the communications session. Examples are headset, speakerphone and group-audio terminal. 3.1.7 HATS hands-free reference point (HATS HFRP): Corresponds to a reference point “n“ from ITU-T P.58, where “n“ is one of the points numbered from 11 to 17 and defined in Tabl
32、e 6A of ITU-T P.58 (coordinates of far-field front point). The HATS HFRP depends on the location(s) of the microphones of the terminal under test: the appropriate axis lip-ring/HATS HFRP shall be as close as possible to the axis lip-ring/HFT microphone under test. 3.1.8 loudspeaking function: Functi
33、on of a handset telephone using a loudspeaker associated with an amplifier as a telephone receiver. It shall be used with a handset to transmit send signals. 3.1.9 single talk: An operation mode, where only one user is speaking. 3.1.10 speakerphone set: A telephone set using a loudspeaker as a telep
34、hone receiver with or without an embedded microphone as a transmitter; it may be used without a handset. 3.2 Abbreviations This Recommendation uses the following abbreviations: AEC Acoustic Echo Control AGC Automatic Gain Control CSS Composite Source Signal DRP ear-Drum Reference Point ERP Ear Refer
35、ence Point HATS Head And Torso Simulator Rec. ITU-T P.342 (06/2009) 3 HFRP Hands-Free Reference Point HFT Hands-Free Terminal LRGP Loudness Rating Guard-ring Position LST LoudSpeaking Terminal MRP Mouth Reference Point RLR Receiving Loudness Rating SLR Sending Loudness Rating TCL Terminal Coupling L
36、oss TCLw Weighted Terminal Coupling Loss 4 Test configuration 4.1 Electrical interface specifications Clauses 4.1 to 4.2 of ITU-T P.310 shall apply in this Recommendation. 4.2 Test arrangement By choosing different test equipments, two methods can be used to make hands-free and loudspeaking measurem
37、ent objectively: the conventional method (using a free-field microphone together with a discrete P.51 artificial mouth) and the HATS method. The artificial mouth shall conform to ITU-T P.51. All measurement values produced by HATS are intended to be free-field equalized. If not specified, HATSs righ
38、t ear is used for the receive measurement. More details such as the exact calibration and equalization procedures as well as the combination of the two ear signals for the purpose of measurements can be found in ITU-T P.581. All effects including test table and measurement equipment are considered a
39、 part of the measurement. NOTE It is recognized that the two test methods may give different results. While the HATS is intended to simulate the hands-free situation in a more realistic way, the conventional set-up is less sensitive to e.g., asymmetric constructions of devices under test. Difference
40、s in the tests results may result from the different orientation of the artificial mouth, from the diffraction effect of the HATS in sending and receiving and from the different physical position of the artificial head compared to the position of the free-field microphone. These effects and their im
41、pact on the measurement are still under study. 4.2.1 Desktop hands-free terminal 4.2.1.1 Conventional method If a free-field microphone together with a discrete P.51 artificial mouth is used, the desktop HFT is placed on a test table according to ITU-T P.340. As shown in Figure 1, the mouth axis and
42、 the microphone axis are coincident with the straight line drawn between point C and point B. For measurements in the sending direction, the artificial mouth is positioned at point C. For receiving direction, the artificial mouth shall be replaced by the measuring microphone. The centre of the micro
43、phone grid shall be positioned at point C, with its axis coincident with line CB. 4 Rec. ITU-T P.342 (06/2009) For TCL and stability loss measurement, the set is positioned but not used. Lip ringB50cmCFigure 1 Measurement configuration for the desktop hands-free terminal using a discrete P.51 artifi
44、cial mouth and a free-field microphone, side view 4.2.1.2 HATS method When a HATS is used, the centre of the lip-ring of HATS shall also be located at point C as defined in Figure 1, but the reference axis of the mouth ought to be horizontal, as illustrated in Figure 2. For TCL and stability loss me
45、asurement, the set is positioned but not used. P.342(09)_F02HATSLip ring centreC30cm40 cmB50cmFigure 2 Measurement configuration for the desktop hands-free terminal using HATS, side view 4.2.2 Double unit desktop speakerphone terminal For desktop speakerphone terminals with detached microphone and s
46、peaker, the standard test position is shown in Figure 3. For desktop speakerphone terminals with more pieces, the test arrangement shall be modified to what it is stated in the instruction manual of the terminal under test (TUT). Rec. ITU-T P.342 (06/2009) 5 P.342(09)_F03Position ofsingle unit HFTCe
47、ntre linethroughhousing600 mmFront edgeof test table400mmPosition of double unit HFT48.6ABFigure 3 Measurement configuration for the desktop speakerphone terminal with detached microphone and speaker (top view) 4.2.3 Other types of hands-free terminals Group-audio terminals or speakerphones designed
48、 for non-desktop positioning, for example, videophony and multimedia terminals, should be tested with the appropriate position. This position shall be defined as the recommended test position (RTP). The RTP should be obtained from the manufacturer, and should be based on the products intended use. I
49、f RTP has not been defined, then the HATS HFRP will be point n (far field) from Table 6A of ITU-T P.58. Headset terminal positioning is described in ITU-T P.310. 4.2.4 Loudspeaking function 4.2.4.1 Conventional method When a free-field microphone together with a discrete P.51 artificial mouth is used, measurements in the sending direction shall be made with the handset placed at LRGP as described in ITU-T P.64. Receiving measurements of loudspeaking function are made with the same test position employed in deskto
