1、 International Telecommunication Union ITU-T P.79TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (11/2007) SERIES P: TELEPHONE TRANSMISSION QUALITY, TELEPHONE INSTALLATIONS, LOCAL LINE NETWORKS Measurements related to speech loudness Calculation of loudness ratings for telephone sets ITU-T Recommend
2、ation P.79 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.300 Transmission standards Series
3、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 multimedia services Series P.900 Transmiss
4、ion 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.79 (11/2007) i ITU-T Recommendation P.79 Calculation of loudness ratings for telephone sets Summary ITU-T Recommendation P.79 describes the preferred me
5、thod for calculating loudness ratings mainly in the case of local telephone systems which transmit a band of frequencies not exceeding about 180-4500 Hz. The purpose of using loudness ratings for telephone sets is two-fold: first, to provide the transmission planner with an adequate measure of how t
6、he sets perform in the network; second, to enable valid and unambiguous comparison between sets. Therefore, to avoid confusion, this version of this Recommendation contains only those telephone set loudness ratings which are of interest for these purposes. The current revision of ITU-T Recommendatio
7、n P.79 is intended to clarify the application fields for Annexes A and G. This Recommendation incorporates in Annex A the description of narrow-band loudness ratings which is applicable for narrow-band and “dual-mode“ narrow-band/wideband end-to-end transmission, including terminals. Annex G is inte
8、nded to apply only for end-to-end wide-band transmission (100 Hz to 7 kHz) between wideband terminals. Source ITU-T Recommendation P.79 was approved on 13 November 2007 by ITU-T Study Group 12 (2005-2008) under the ITU-T Recommendation A.8 procedure. ii ITU-T Rec. P.79 (11/2007) FOREWORD The Interna
9、tional 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, oper
10、ating 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 turn, p
11、roduce 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 In
12、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.g. i
13、nteroperability 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 sugges
14、t 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 eviden
15、ce, 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 may
16、 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 be
17、reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. P.79 (11/2007) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Abbreviations and acronyms 2 4 Loudness rating parameters for telephone sets. 2 5 General algorithm for loudness rating calculations 3 6 Calculati
18、on of SLR and RLR 3 7 Calculation of STMR 4 8 Calculation of LSTR. 5 Annex A Fundamental principles of loudness rating calculations 6 A.1 Introduction 6 A.2 Definitions and symbols concerning sound pressures, sensitivities and transmission losses . 6 A.3 Structure of the theoretical model 8 A.4 Valu
19、es of the parameters 12 A.5 Calculation of loudness ratings 15 Annex B Fundamental principles of calculation of sidetone masking 21 B.1 Calculation from first principles. 21 B.2 Calculation of STMR using W weights 22 B.3 Comments on sealed versus unsealed conditions for the calculation of STMR . 23
20、B.4 Calculation of LSTR using W weights . 24 Annex C An alternative form of the loudness rating algorithm 25 Annex D Weighting coefficients for the band 100-8000 Hz 27 Annex E Calculation of the listeners sidetone factor D . 28 E.1 General . 28 E.2 Non-linear microphones and/or circuitry . 28 E.3 Li
21、near microphones and circuitry. 28 Annex F Computation of the sidetone sensitivity SmeST30 Annex G Wideband loudness rating algorithm. 31 ITU-T Rec. P.79 (11/2007) 1 ITU-T Recommendation P.79 Calculation of loudness ratings for telephone sets 1 Scope This Recommendation describes the preferred metho
22、d for calculating loudness ratings in the following cases: Narrow-band local telephone systems (which transmit a band of frequencies not exceeding about 180-4500 Hz). “Dual-Mode“ narrow-band/wideband end-to-end transmissions, including terminals, (respectively 300-3400 Hz and 100-7000 Hz). Wide-band
23、 only end-to-end transmission (100 Hz to 7 kHz) between wide-band terminals. The purpose of using loudness ratings for telephone sets is two-fold: first, to provide the transmission planner with an adequate measure of how the sets perform in the network; second, to enable valid and unambiguous compa
24、rison between sets. Therefore, to avoid confusion, this version of this Recommendation contains only those telephone set loudness ratings which are of interest for these purposes. Annex A contains the fundamental principles of loudness rating calculations and explains the relations between ITU-T P.7
25、6, ITU-T P.78 and this Recommendation as well as the physical basis of this Recommendation. Annex B explains the fundamental concept of the sidetone masking rating (STMR) used for evaluation of the talkers sidetone. Annex C gives an alternative form of the loudness rating algorithm which is useful f
26、or estimating the relative importance of how the sensitivity in different frequency bands influences the loudness rating value. Annex D provides, as a reference only, Wi-weights for OLR, SLR and RLR over the wider band 100-8000 Hz. Annex E describes how the listeners sidetone factor D can be determi
27、ned. Annex F shows how the sidetone sensitivity SmeSTcan be computed from the send and receive sensitivity and impedance data. Annex G gives a set of W weights suitable for the calculation of sending and receiving loudness ratings of wideband (100 to 7000 Hz) only terminals. 2 References The followi
28、ng 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 valid. All Recommendations and other references are subject to revision; users of this Recomme
29、ndation 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 is regularly published. The reference to a document within this Recommendation does not gi
30、ve it, as a stand-alone document, the status of a Recommendation. ITU-T G.111 ITU-T Recommendation G.111 (1993), Loudness ratings (LRs) in an international connection. ITU-T P.48 ITU-T Recommendation P.48 (1988), Specification for an intermediate reference system. 2 ITU-T Rec. P.79 (11/2007) ITU-T P
31、.51 ITU-T Recommendation P.51 (1996), Artificial mouth. ITU-T P.57 ITU-T Recommendation P.57 (2005), Artificial ears. ITU-T P.64 ITU-T Recommendation P.64 (2007), Determination of sensitivity/frequency characteristics of local telephone systems. ITU-T P.76 ITU-T Recommendation P.76 (1988), Determina
32、tion of loudness ratings; fundamental principles. ITU-T P.78 ITU-T Recommendation P.78 (1996), Subjective testing method for determination of loudness ratings in accordance with Recommendation P.76. ITU-T P.310 ITU-T Recommendation P.310 (2003), Transmission characteristics for telephone band (300-3
33、400 Hz) digital telephones. ITU-T P.340 ITU-T Recommendation P.340 (2000), Transmission characteristics and speech quality parameters of hands-free terminals. ITU-T Handbook ITU-T Handbook on Telephonometry, 1992. 3 Abbreviations and acronyms This Recommendation uses the following abbreviations and
34、acronyms: JLR Junction Loudness Rating LSTR Listener Sidetone Rating OLR Overall Loudness Rating RLR Receive Loudness Rating SLR Send Loudness Rating STMR Sidetone Masking Rating 4 Loudness rating parameters for telephone sets In transmission planning and for regulatory purposes, the following loudn
35、ess rating parameters for telephone sets are of interest: send loudness rating (SLR); receive loudness rating (RLR). For 2-wire sets, SLR and RLR are to be determined for an appropriate range of feeding currents and subscriber cables. The talkers sidetone is characterized by the sidetone masking rat
36、ing (STMR), usually determined for a representative range of terminations. The listeners sidetone is characterized by the listeners sidetone rating (LSTR), which is a characterization of the room noise picked up via the electric sidetone path. However, in transmission planning it is often more usefu
37、l to evaluate listeners sidetone performance of a set indirectly by the difference: D = LSTR STMR D is a parameter of the telephone set which is independent of the termination. Therefore, the formulae for calculation of D are given in Annex E. ITU-T Rec. P.79 (11/2007) 3 5 General algorithm for loud
38、ness rating calculations The general algorithm for calculation of loudness ratings (LRs) is of the form: ()=211.01010log10NNiWSmiimLR (5-1) where: m a constant (in the order of 0.2). The summation is to be performed at frequencies Fi, spaced 1/3 octave apart. Wiweighting coefficient (different for t
39、he various LRs). Sithe sensitivity at frequency Fiof the electro-acoustic path under consideration. NOTE 1 Siis to be determined by the methods described in ITU-T P.64 for analogue 2-wire handsets. Digital sets are measured according to clause B.6 of ITU-T P.310 and hands-free sets according to clau
40、se 4.5.1 of ITU-T P.340. NOTE 2 One can also use the designation “electro-acoustic loss“ Li= Si. NOTE 3 When calculating SLR and RLR, one must only include those parts of the frequency band where an actual signal transmission can occur in order to ensure that the additivity property of LRs is retain
41、ed. Therefore, only the frequency band 200-4000 Hz is used. 6 Calculation of SLR and RLR In Equation 5-1, m = 0.175. The weighting coefficients Wsiand Wriare given in Table 1. Table 1 Weighting factors Wifor SLR and RLR Band No. Mid-frequency (Hz) Send WsiReceive Wri 4 200 76.9 85.0 5 250 62.6 74.7
42、6 315 62.0 79.0 7 400 44.7 63.7 8 500 53.1 73.5 9 630 48.5 69.1 10 800 47.6 68.0 11 1000 50.1 68.7 12 1250 59.1 75.1 13 1600 56.7 70.4 14 2000 72.2 81.4 15 2500 72.6 76.5 16 3150 89.2 93.3 17 4000 117.0 113.8 NOTE These weights are 0.3 dB smaller than those provided in the original version of this R
43、ecommendation in the CCITT Blue Book, Vol. V, to allow for the change in loudness of the IRS over the reduced bandwidth. 4 ITU-T Rec. P.79 (11/2007) The Si-values apply as follows. For SLR from the artificial mouth to an (equivalent) 600-ohm electrical interface: Si= SmJ (Fi) (6-1) For RLR from an (
44、equivalent) 600-ohm electrical interface to the artificial ear, including a consideration of the earcap leakage LE: Si= SJe(Fi) LE(Fi) (6-2) Normally, the receive sensitivity is measured with the artificial ear acoustically sealed to the earcap (see ITU-T P.64). If the earcap is of a conventional sh
45、ape and the receiver is somewhat similar to the type used in the IRS, the LE-values in Table 2 are to be used. Table 2 Leakage correction LEused for sealed measurements on an IRS-type receiver Frequency (Hz) LE(dB) Frequency (Hz) LE (dB) 200 8.4 1000 2.3 250 4.9 1250 1.2 315 1.0 1600 0.1 400 0.7 200
46、0 3.6 500 2.2 2500 7.4 630 2.6 3150 6.7 800 3.2 4000 8.8 If a more advanced artificial ear, incorporating a simulated leak, is used, no LE-correction is needed, i.e., LE= 0 in Equation 6-2. (See also ITU-T P.57.) Also for hands-free telephones, LE= 0. 7 Calculation of STMR In Equation 5-1, m = 0.225
47、. The weighting coefficients WMSIare given in Table 3. The Si-values apply from the artificial mouth to the artificial ear (for the same set) via the electric sidetone path, caused by impedance mismatches for analogue 2-wire sets or a designed bridging circuit between send and receive for digital se
48、ts. Si= SmeST (Fi) (7-1) NOTE Most often the sidetone measuring set-up consists of an unloaded subscriber line (or its electrical equivalent) terminated by a physical, nominal impedance which may be complex. Then the curve SmeST(f) can be adequately represented by the frequency points spaced 1/3 oct
49、ave apart. However, if the termination consists of a 2-wire port of a digital exchange, the sidetone response SmeST(f) may vary very rapidly with frequency, so that the 1/3-octave spacing is too coarse. This happens when the loss through the exchange is low and there are strong reflections at the other 2-wire port of the connection. In this case, a talker would notice both sidetone and echo so that a formal calculation of STMR is less relevant. ITU-T Rec. P.79 (11/2007) 5 Table 3 Weighting f
