1、 International Telecommunication Union ITU-T P.341TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (06/2005) SERIES P: TELEPHONE TRANSMISSION QUALITY, TELEPHONE INSTALLATIONS, LOCAL LINE NETWORKS Subscribers lines and sets Transmission characteristics for wideband (150-7000 Hz) digital hands-free tel
2、ephony terminals ITU-T Recommendation P.341 ITU-T P-SERIES RECOMMENDATIONS TELEPHONE TRANSMISSION QUALITY, TELEPHONE INSTALLATIONS, LOCAL LINE NETWORKS Vocabulary and effects of transmission parameters on customer opinion of transmission quality Series P.10 Subscribers lines and sets Series P.30 P.3
3、00 Transmission standards Series 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 quality Series P.80 P.800Audiovisual quality in multimedi
4、a services Series P.900 Transmission performance and QoS aspects of IP end-points Series P.1000 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. P.341 (06/2005) i ITU-T Recommendation P.341 Transmission characteristics for wideband (150-7000 Hz) digital hands-free t
5、elephony terminals Summary This revised Recommendation provides audio performance requirements for wideband audio (7 kHz) hands-free telephones. Associated test methods for verifying wideband audio performance are contained in Annex A. Requirements and test methods are specified for the major audio
6、transmission parameters affecting wideband audio, including levels, frequency response, noise, distortion, spurious signals and echo path. Wideband audio represents a considerable departure from traditional telephony, offering significantly improved quality. The main revision encompassed by this ver
7、sion of the Recommendation is to adopt the wideband loudness rating algorithm as in Annex G/P.79. Source ITU-T Recommendation P.341 was approved on 6 June 2005 by ITU-T Study Group 12 (2005-2008) under the ITU-T Recommendation A.8 procedure. ii ITU-T Rec. P.341 (06/2005) FOREWORD The International T
8、elecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. 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 t
9、hem with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication 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
10、-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information 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 use
11、d for conciseness to indicate both a telecommunication administration and a recognized operating agency. 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 R
12、ecommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some 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 an
13、y party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation 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 Prope
14、rty Rights, whether asserted by ITU members or others outside of the Recommendation development process. 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, imp
15、lementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2005 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec
16、. P.341 (06/2005) iii CONTENTS Page 1 Scope 1 2 Normative references 1 3 Definitions and abbreviations. 2 4 Sending characteristics . 2 4.1 Loudness rating 2 4.2 Sensitivity/frequency characteristics 3 4.3 Noise. 3 4.4 Distortion 4 4.5 Discrimination against out-of-band input signals. 4 5 Receiving
17、characteristics 4 5.1 Loudness rating 4 5.2 Sensitivity/frequency characteristics 5 5.3 Noise. 5 5.4 Distortion 6 5.5 Spurious out-of-band receiving signals 6 6 Echo path loss characteristics . 6 6.1 Weighted Terminal Coupling Loss (TCLw) 6 6.2 Stability loss . 6 7 Delay. 6 Annex A Objective measure
18、ment methods for wideband hands-free telephones using the reference codec approach 7 A.1 Introduction 7 A.2 Electrical interface specifications. 7 A.3 Electro-acoustic measurement considerations 8 A.4 Sending measurements . 12 A.5 Receiving measurements 13 A.6 Echo path loss measurements. 14 A.7 Del
19、ay measurements. 14 ITU-T Rec. P.341 (06/2005) 1 ITU-T Recommendation P.341 Transmission characteristics for wideband (150-7000 Hz) digital hands-free telephony terminals 1 Scope This Recommendation provides audio performance requirements and test methods for hands-free telephones capable of transmi
20、tting an audio bandwidth extending beyond the conventional telephony bandwidth of 300 to 3400 Hz, to a bandwidth of approximately 150 to 7000 Hz. Such telephones are known as wideband audio telephones, and will make use of digital encoding schemes such as in ITU-T Rec. G.722 1. Wideband audio teleph
21、ones are expected to be used in new services such as high quality audio conferencing, videoconferencing and multimedia applications. The requirements listed in this Recommendation are primarily applicable to telephones using G.722 1 encoding at 64 kbit/s, but should also be used as the basis of requ
22、irements for other wideband audio encoding schemes. This is still under study in ITU-T Study Group 12. The measurement method for delay is still under study. General information on HFTs, which includes switching characteristics, can be found in ITU-T Rec. P.340 3 and information on acoustic echo con
23、trollers in ITU-T Rec. G.167 16. For loudspeaking telephones (see ITU-T Rec. P.10 15) which do not provide full hands-free operation, the relevant parts of this Recommendation may be used. Conventional telephone band (300-3400 Hz) digital hands-free telephones using encoding according to ITU-T Recs
24、G.711 12 and G.726 13 are covered by ITU-T Rec. P.342 7. 2 Normative references The following ITU-T 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 val
25、id. All Recommendations and other references are subject to revision; 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 ITU-T Recommendations
26、 is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. 1 ITU-T Recommendation G.722 (1988), 7 kHz audio coding within 64 kbit/s. 2 ITU-T Recommendation P.310 (2003), Transmission characteristics for
27、 telephone band (300-3400 Hz) digital telephones. 3 ITU-T Recommendation P.340 (2000), Transmission characteristics and speech quality parameters of hands-free terminals. 4 ITU-T Recommendation P.51 (1996), Artificial mouth. 5 ITU-T Recommendation P.57 (2002), Artificial ears. 6 ITU-T Recommendation
28、 P.64 (1999), Determination of sensitivity/frequency characteristics of local telephone systems. 7 ITU-T Recommendation P.342 (2000), Transmission characteristics for telephone band (300-3400 Hz) digital loudspeaking and hands-free telephony terminals. 8 ITU-T Recommendation P.79 (1999), Calculation
29、 of loudness ratings for telephone sets. 2 ITU-T Rec. P.341 (06/2005) 9 IEC 61672-2 (2003), Electroacoustics Sound level meters Part 2: Pattern evaluation tests. 10 ISO 3:1973, Preferred numbers Series of preferred numbers. 11 ITU-T Recommendation G.122 (1993), Influence of national systems on stabi
30、lity and talker echo in international connections. 12 ITU-T Recommendation G.711 (1988), Pulse code modulation (PCM) of voice frequencies. 13 ITU-T Recommendation G.726 (1990), 40, 32, 24, 16 kbit/s Adaptive Differential Pulse Code Modulation (ADPCM). 14 ITU-T Recommendation P.311 (2005), Transmissi
31、on characteristics for wideband (150-7000 Hz) digital handset telephones. 15 ITU-T Recommendation P.10 (1998), Vocabulary of terms on telephone transmission quality and telephone sets. 16 ITU-T Recommendation G.167 (1993), Acoustic echo controllers. 17 ITU-T Recommendation P.501 (2000), Test signals
32、 for use in telephonometry. 3 Definitions and abbreviations This Recommendation defines the following terms: 3.1 Acoustic Reference Level (ARL): The acoustic level at MRP which results in a 10 dBm0 output at the digital interface. 3.2 Hands-free Reference Point (HFRP): A point located on the axis of
33、 the artificial mouth, at 50 cm from the outer plane of the lip ring, where the level calibration is made under free-field conditions. It corresponds to measurement point No. 11 defined in ITU-T Rec. P.51 4. This Recommendation also uses the following abbreviations. Relevant abbreviations in ITU-T R
34、ec. P.10 15 will also apply: CSS Composite Source Signal HFT Hands-free Terminal MRP Mouth Reference Point RLR Receiving Loudness Rating SLR Sending Loudness Rating TCL Terminal Coupling Loss TCLw Weighted Terminal Coupling Loss 4 Sending characteristics 4.1 Loudness rating Following the approach us
35、ed for narrow-band hands-free telephones in ITU-T Rec. P.340 3, the levels in the hands-free send direction are related to those in wideband handset mode (see ITU-T Rec. P.311 14) with an allowance of 5 dB for higher talking levels and the difference in speaking position. The value of SLR shall ther
36、efore be +9 dB, measured in terms of wideband loudness rating according to Annex G/P.79 8. NOTE The overload point for wideband audio is currently defined as +9 dBm0 1. Should this overload point be changed in future revisions of 1, then the Loudness Rating requirements of this Recommendation should
37、 also be revised accordingly. The same concept applies in case this Recommendation is used for ITU-T Rec. P.341 (06/2005) 3 specifying the electroacoustic requirements of digital telephone sets using wideband audio coders with a different overload point. 4.2 Sensitivity/frequency characteristics The
38、 sending sensitivity/frequency characteristics shall fall between the upper and lower limits given in Table 1, and shown in Figure 1. All sensitivities are in dB on an arbitrary scale. Table 1/P.341 Sending sensitivity/frequency characteristics Frequency (Hz) Upper limit (dB) Lower limit (dB) 100 4
39、125 4 7 200 4 4 1000 4 4 5000 (Note) 4 6300 9 7 8000 9 NOTE The limits for intermediate frequencies lie on a straight line drawn between the given values on a logarithmic (frequency) linear (dB) scale. Figure 1/P.341 Hands-free sending characteristic 4.3 Noise With the microphone acoustically muted
40、(equivalent to an ambient noise level of 30 dBA), the noise in the sending direction at the digital interface shall not exceed 68 dBm0 (A-weighted). 4 ITU-T Rec. P.341 (06/2005) 4.4 Distortion The distortion in the sending direction shall be measured in terms of the total distortion (harmonic and qu
41、antizing) arising from the application of 200 Hz, 1 kHz and 6 kHz tones applied separately. The limits shall be as shown in Table 2. Table 2/P.341 Distortion in sending direction Signal-to-distortion ratio limit (dB) Sending level (dB re ARL) 200 Hz 1 kHz 6 kHz +18 to 20 29.0 35.0 29.0 30 25.0 26.5
42、25.0 46 11.0 12.5 11.0 NOTE 1 These limits only apply up to the maximum sound pressure level which can be produced by the artificial mouth (+10 dBPa). NOTE 2 The limits for signal-to-total distortion ration for intermediate sending levels lie on straight lines drawn between the given values on a lin
43、ear (dB sending level) linear (dB ratio) scale. 4.5 Discrimination against out-of-band input signals The level of any in-band image frequencies resulting from application of input signals at 8 kHz and above shall be attenuated by at least 25 dB compared to the output level of a 1-kHz input signal. 5
44、 Receiving characteristics 5.1 Loudness rating Following the approach used for narrow-band hands-free telephones in ITU-T Rec. P.340 3, the levels in the hands-free receiving direction are, in principle, the same as those in wideband handset mode. The nominal value of RLR shall then be +2 dB. The RL
45、R value shall be met for at least one setting of the receiving volume control (when manually operated). For HFTs equipped only with automatic (receiving) gain control, the RLR measured with an input signal of 15 dBm0 shall be higher by 10 to 15 dB than the RLR measured with an input signal of 30 dBm
46、0. The nominal RLR shall be included in the measured range. The RLR measured with an input signal of 30 dBm0 shall be 7 dB. NOTE The overload point for wideband audio is currently defined as +9 dBm0 1. Should this overload point be changed in future revisions of 1, then the Loudness Rating requireme
47、nts of this Recommendation should also be revised accordingly. The same concept applies in case this Recommendation is used for specifying the electroacoustic requirements of digital telephone sets using wideband audio coders with a different overload point. ITU-T Rec. P.341 (06/2005) 5 5.2 Sensitiv
48、ity/frequency characteristics The receiving sensitivity/frequency characteristics shall fall between the upper and lower limits given in Table 3, and shown in Figure 2. All sensitivities are in dB on an arbitrary scale. Table 3/P.341 Receiving sensitivity/frequency characteristics Frequency (Hz) Upp
49、er limit (dB) Lower limit (dB) 100 6 160 6 7 200 6 4 250 6 4 400 4 4 1000 4 4 5000 4 4 6300 4 7 8000 4 NOTE The limits for intermediate frequencies lie on straight lines drawn between the given values on a logarithmic (frequency) linear (dB) scale. Figure 2/P.341 Hands-free receiving characteristic 5.3 Noise The A-weighted quiescent noise in the receiving direction shall not exceed 49 dBPa (A). If a receiving volume control is provided, the requiremen
