1、 International Telecommunication Union ITU-T P.64TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (11/2007) SERIES P: TELEPHONE TRANSMISSION QUALITY, TELEPHONE INSTALLATIONS, LOCAL LINE NETWORKS Objective electro-acoustical measurements Determination of sensitivity/frequency characteristics of local
2、telephone systems Recommendation ITU-T P.64 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. Rec. ITU-T P.64 (11/2007) i Recommendation ITU-T P.64 Determination of sensitivity/frequency characteristics of local telephone syst
5、ems Summary Recommendation ITU-T P.64 is mainly concerned with electro-acoustical measurements required for supplying sensitivity/frequency characteristics suitable for use in calculating loudness ratings, or estimating other subjectivity-determined quantities. For this purpose, measurements under r
6、eal 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-consuming and not reproducible with
7、 great precision. This Recommendation describes measurement methods using recommended forms of artificial mouths and artificial ears (see Recommendations ITU-T P.51 and P.57). This Recommendation applies mainly to local telephone systems (LTSs) with handset telephones; however, the principles also a
8、pply to other types of telephones. Annexes D and E define handset positions to be used with HATS according to P.58 and P.57 type 3.2, 3.3 and 3.4 artificial ears. Allowance is given to placing the handset in a way which best represents its intended use. Annex F describes correspondence between measu
9、rements using the loudness rating guard-ring position (LRGP) and the head and torso simulator (HATS) position. Source Recommendation ITU-T P.64 was approved on 13 November 2007 by ITU-T Study Group 12 (2005-2008) under Recommendation ITU-T A.8 procedure. ii Rec. ITU-T P.64 (11/2007) FOREWORD The Int
10、ernational Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical,
11、operating and tariff questions and issuing Recommendations on them 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 tur
12、n, 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 information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE
13、 In this Recommendation, the expression “Administration“ is used 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.
14、g. interoperability or applicability) and compliance with the Recommendation 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 su
15、ggest that compliance with the Recommendation is required of any 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 ev
16、idence, validity or applicability of claimed Intellectual Property 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
17、 may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2008 All rights reserved. No part of this publication may
18、 be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T P.64 (11/2007) iii CONTENTS Page 1 Scope 1 2 References 1 3 Abbreviations . 2 4 Sending sensitivities of the LTS. 2 5 Receiving sensitivities of the LTS 3 6 Artificial mouth and voice 4 7 Artificial ear
19、. 4 8 Definition of sending sensitivity of an LTS . 4 9 Definition of receiving sensitivity of an LTS. 5 10 Definitions of talker and listener sidetone sensitivities of an LTS. 5 11 Methods for determining SmJ, SJe, SmeST, SRNSTand SM6 Annex A Definitions of mouth reference point and ear reference p
20、oint 11 Annex B The application of complex terminating impedances when measuring SLR and RLR . 12 B.1 Complex impedance terminations 12 B.2 Impedance converter 12 B.3 Differences when measuring a telephone set with a complex impedance using 600 ohm terminations . 15 Annex C Definition of the speakin
21、g position for measuring loudness ratings of handset telephones. 18 C.1 Geometry defining a speaking position 18 C.2 Geometry defining a change in speaking position . 19 C.3 Simplification through the use of the position of the ear reference point 19 C.4 Vector representation of the reference points
22、 19 Annex D Definition of handset positions for measuring loudness ratings and frequency responses using the P.57 type 3.4 artificial ear on HATS 21 D.1 General . 21 D.2 Definition of the standard handset position 21 D.3 Definition of the flat handset position 22 D.4 Definition of the alternative ha
23、ndset position for measuring loudness ratings and frequency responses using the P.57 type 3.4 artificial ear on HATS . 22 Annex E Definition of handset positions for measuring loudness ratings and frequency responses using the P.57 types 3.2 and 3.3 artificial ear on HATS 24 E.1 Definition of standa
24、rd handset position for measuring loudness ratings and frequency responses using the P.57 types 3.2 and 3.3 artificial ear on HATS . 24 iv Rec. ITU-T P.64 (11/2007) Page E.2 Definition of the alternative handset position for measuring loudness ratings and frequency responses using the P.57 type 3.3
25、artificial ear on HATS . 25 Annex F Correspondence between measurements using the LRGP and the HATS position . 27 Bibliography 28 Rec. ITU-T P.64 (11/2007) 1 Recommendation ITU-T P.64 Determination of sensitivity/frequency characteristics of local telephone systems 1 Scope The sending, receiving or
26、sidetone sensitivity/frequency characteristic of a local telephone system (LTS) is usually measured directly. NOTE 1 The sending, receiving or sidetone sensitivity/frequency characteristic can also be calculated provided that the relevant information of the telephone line and feeding bridge is known
27、. Some of the information required for sidetone is outside the scope of existing Recommendations. NOTE 2 The same principles also apply to the measurement of microphones and earphones. Since electro-acoustical measurements of the type being considered may be required for different purposes, it is im
28、portant to distinguish the following: a) supplying the designer of a transducer with information concerning the success he has achieved in aiming at a given sensitivity/frequency response; b) checking that the manufactured product meets the specified requirements; c) supplying sensitivity/frequency
29、characteristics suitable for use in calculating loudness ratings or estimating other subjectivity-determined quantities. This Recommendation is mainly concerned with c), but the principle is also applicable to a) and b). For these purposes, especially for c), measurements under real conditions must
30、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-consuming and not reproducible with great precision. Th
31、is Recommendation describes measurement methods using recommended forms of artificial mouths and artificial ears (see ITU-T P.51 and ITU-T P.57). This Recommendation applies mainly to LTSs with handset telephones. However, the principles also apply to other types of telephones. Specific consideratio
32、ns for headsets are described in ITU-T P.380 and, for loudspeaker telephones, ITU-T P.340. See ITU-T P.76 for general principles concerning the determination of loudness ratings. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this
33、 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 to investigate the possibility of applying the most recent editi
34、on 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, the status of a Recommendation. ITU-T G.111 Recommendation ITU-
35、T G.111 (1993), Loudness ratings (LRs) in an international connection. ITU-T P.10 Recommendation ITU-T P.10/G.100 (2006), Vocabulary for performance and quality of service. ITU-T P.50 Recommendation ITU-T P.50 (1999), Artificial voices. ITU-T P.51 Recommendation ITU-T P.51 (1996), Artificial mouth.
36、2 Rec. ITU-T P.64 (11/2007) 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 telephonometry. ITU-T P.76 Recommendation ITU-T P.76 (1988), Determination of loudness ratings; fundamental principles. ITU-T P.78 Recom
37、mendation ITU-T P.78 (1996), Subjective testing method for determination of loudness ratings in accordance with Recommendation P.76. ITU-T P.79 Recommendation ITU-T P.79 (2007), Calculation of loudness ratings for telephone sets. ITU-T P.340 Recommendation ITU-T P.340 (2000), Transmission characteri
38、stics and speech quality parameters of hands-free terminals. ITU-T P.380 Recommendation ITU-T P.380 (2003), Electro-acoustic measurements on headsets. ITU-T Q.552 Recommendation ITU-T Q.552 (2001), Transmission characteristics at 2-wire analogue interfaces of digital exchanges. 3 Abbreviations This
39、Recommendation uses the following abbreviations: DRP Drum Reference Point ECRP EarCap Reference Point EEP Ear canal Entrance Point ERP Ear Reference Point FFT Fast Fourier Transform HATS Head and Torso Simulator LRGP Loudness Rating Guard-ring Position LSTR Listener SideTone Rating LTS Local Telepho
40、ne System MRP Mouth Reference Point RLR Receive Loudness Rating SLR Send Loudness Rating STMR SideTone Masking Rating 4 Sending sensitivities of the LTS For the present purposes, the sending sensitivity of a local telephone system is specified in terms of the free-field sound pressure at a reference
41、 point in front of the mouth1, 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
42、 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 _ 1The mouth reference point used in this Recommendation is defined in Annex A. Rec. ITU-T P.64 (11/2007) 3 position in front of the mouth and the outp
43、ut 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-field sound pressure and that of the electrical output from the microphone. Artificial mouths suffer from imperfect representation of the source impeda
44、nce and field distribution that applies to real mouths. 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
45、 mouthpiece properly with respect to an ear reference point; this ensures that longer handsets are measured with a greater mouth-to-microphone distance than is the case for shorter handsets. The success of using a given handset measuring position for measurement of sensitivity/frequency characterist
46、ics 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 this Recommendation, the telephone handset shall be located as defined in Annex C. The
47、 handset positions to be used with HATS according to ITU-T P.58 and type 3.3 and 3.4 pinna simulators are defined in Annexes D and E. Special problems are encountered when making measurements with real mouths and real voices, even under controlled talking conditions. Under such circumstances, the so
48、und 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 a
49、nechoic surroundings and is affected by obstruction from the handset under test. Other methods have been also tried and none seem satisfactory so far. 5 Receiving sensitivities of the LTS The type 1 artificial ear (see ITU-T P.57 to be specified in b-IEC 60318-1) 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
