1、 I n t e r n a t i o n a l T e l e c o m m u n i c a t i o n U n i o n ITU-T P.834 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (06/2015) SERIES P: TERMINALS AND SUBJECTIVE AND OBJECTIVE ASSESSMENT METHODS Methods for objective and subjective assessment of speech quality Methodology for the deriv
2、ation of equipment impairment factors from instrumental models Recommendation ITU-T P.834 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
3、characteristics Series P.30 P.300 Reference systems 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 speech quality Series P.80 P.80
4、0 Audiovisual quality in multimedia services Series P.900 Transmission performance and QoS aspects of IP end-points Series P.1000 Communications involving vehicles Series P.1100 Models and tools for quality assessment of streamed media Series P.1200 Telemeeting assessment Series P.1300 Statistical a
5、nalysis, evaluation and reporting guidelines of quality measurements Series P.1400 Methods for objective and subjective assessment of quality of services other than voice services Series P.1500 For further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T P.834 (06/2015) i Recom
6、mendation ITU-T P.834 Methodology for the derivation of equipment impairment factors from instrumental models Summary Recommendation ITU-T P.834 gives a methodology for deriving equipment impairment factors (Ies) for digital signal processing devices, namely low bit-rate codecs. The Ie values are in
7、tended to be used as an input to the E-model (see Recommendation ITU-T G.107). The methodology specified in this Recommendation makes use of instrumental models (so-called “objective methods“), e.g., of the model defined in Recommendation ITU-T P.862. It is to be considered as supplementary to the m
8、ethodology based on auditory listening-only tests, described in Recommendation ITU-T P.833. It will provide valid Ie values only for those codecs for which the used instrumental model produces meaningful estimations. This Recommendation includes an electronic attachment containing speech material. H
9、istory Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T P.834 2002-07-14 12 11.1002/1000/6084 1.1 ITU-T P.834 (2002) Cor. 1 2005-01-27 12 11.1002/1000/7828 2.0 ITU-T P.834 2015-06-29 12 11.1002/1000/12516 Keywords E-model, equipment impairment factor, impairment factor method, instru
10、mental model, low bit-rate codecs, objective method. _ * To access the Recommendation, type the URL http:/handle.itu.int/ in the address field of your web browser, followed by the Recommendations unique ID. For example, http:/handle.itu.int/11.1002/1000/11830-en. ii Rec. ITU-T P.834 (06/2015) FOREWO
11、RD The International 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 t
12、echnical, 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 whi
13、ch, 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 information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and
14、 IEC. NOTE 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
15、 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 other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words
16、 does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTSITU 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 concer
17、ning the evidence, 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 pat
18、ents, which 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 2015 All rights reserved. No part of this publ
19、ication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T P.834 (06/2015) iii Table of Contents Page 1 Scope . 1 2 References . 1 3 Introduction . 2 4 Experimental set-up and data processing . 3 4.1 Input speech material 4 4.2 Reference conditions 4
20、4.3 Processing of speech material 6 4.4 Calculation of MOS estimations using the instrumental model . 7 5 Derivation of equipment impairment factors 7 6 Interpretation of instrumentally derived equipment impairment factor values 9 Annex A Speech material . 10 Appendix I Calculation of equipment impa
21、irment factors from scores provided by the instrumental model described in ITU-T P.862 . 16 Bibliography. 17 Electronic attachment: Freely-available speech material described within the Recommendation. Rec. ITU-T P.834 (06/2015) 1 Recommendation ITU-T P.834 Methodology for the derivation of equipmen
22、t impairment factors from instrumental models 1 Scope This Recommendation1 describes the methodology for deriving equipment impairment factors (Ies) using instrumental models. The equipment impairment factors derived by this methodology are intended to be used in the E-model (see ITU-T G.107). The m
23、ethodology is to be considered as supplementary to the one based on auditory listening-only tests described in ITU-T P.833. It will provide valid Ie values only for those codecs for which the instrumental model used produces meaningful estimations. 2 References The following ITU-T Recommendations an
24、d 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 Recommendation are therefore encou
25、raged 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 give it, as a stand-alone doc
26、ument, the status of a Recommendation. ITU-T G.107 Recommendation ITU-T G.107 (2015), The E-model: a computational model for use in transmission planning. ITU-T G.113 Recommendation ITU-T G.113 (2007), Transmission impairments due to speech processing. ITU-T G.711 Recommendation ITU-T G.711 (1988),
27、Pulse code modulation (PCM) of voice frequencies. ITU-T G.712 Recommendation ITU-T G.712 (2001), Transmission performance characteristics of pulse code modulation channels. ITU-T G.726 Recommendation ITU-T G.726 (1990), 40, 32, 24, 16 kbit/s Adaptive Differential Pulse Code Modulation (ADPCM). ITU-T
28、 G.727 Recommendation ITU-T G.727 (1990), 5-, 4-, 3- and 2-bit/sample embedded adaptive differential pulse code modulation (ADPCM). ITU-T G.728 Recommendation ITU-T G.728 (2012), Coding of speech at 16 kbit/s using low-delay code excited linear prediction. ITU-T G.729 Recommendation ITU-T G.729 (201
29、2), Coding of speech at 8 kbit/s using conjugate-structure algebraic-code-excited linear prediction (CS-ACELP). ITU-T P.800 Recommendation ITU-T P.800 (1996), Methods for subjective determination of transmission quality. ITU-T P.810 Recommendation ITU-T P.810 (1996), Modulated noise reference unit (
30、MNRU). _ 1 This Recommendation includes an electronic attachment containing speech material. 2 Rec. ITU-T P.834 (06/2015) ITU-T P.830 Recommendation ITU-T P.830 (1996), Subjective performance assessment of telephone-band and wideband digital codecs. ITU-T P.833 Recommendation ITU-T P.833 (2001), Met
31、hodology for derivation of equipment impairment factors from subjective listening-only tests. ITU-T P.862 Recommendation ITU-T P.862 (2001), Perceptual evaluation of speech quality (PESQ): An objective method for end-to-end speech quality assessment of narrowband telephone networks and speech codecs
32、. ITU-T P.Sup23 ITU-T P-series Recommendations Supplement 23 (1998), ITU-T coded-speech database. 3 Introduction The equipment impairment factor method of ITU-T G.113 is now the only one recommended by ITU-T for describing the subjective effects of digital processes other than pure pulse code modula
33、tion (PCM) on the integral quality for transmission planning purposes. It is based on the principle that individual transmission impairments can be transformed into “psychological factors“, and that these psychological factors are additive on a “psychological scale“. It is assumed that the transmiss
34、ion rating scale underlying the E-model of ITU-T G.107 has the properties of such a “psychological scale“. In transmission planning of modern telecommunication networks, it is important to consider the combined effects of different types of impairments occurring simultaneously in a connection. This
35、is performed by computational models like the E-model. Individual sources of degradations, such as a non-optimum overall loudness rating or sidetone path attenuation, talker echo attenuation and delay, quantizing distortion, and absolute delay, are transformed into so-called impairment factors. Degr
36、adations due to low bit-rate codecs are taken into account by means of an equipment impairment factor. Whereas interrelationships exist between the other impairment factors due to the underlying instrumentally measurable quantities of the connection (e.g., loudness ratings), the equipment impairment
37、 factor is, by its very definition, independent of all the other impairment factors. It is only dependent on the digital process whose perceptual characteristics it aims to model. The final transmission rating for the entire connection is calculated from all the individual impairment factors, by sub
38、tracting them from a basic signal-to-noise ratio. For asynchronous tandems of multiple codecs of the same type, or of multiple codecs of different types, it is assumed that individual equipment impairment factors are additive. The overall equipment impairment factor for the chain of codecs is then c
39、alculated as a simple sum of all the individual Ies. Experimental test data provide evidence that this simple additivity is not satisfied for all the potential combinations of codecs b-ITU-T COM12-69 and b-Mller. In some cases, order effects exist, i.e., the tandem of codec A followed by codec B res
40、ults in a different degradation to codec B followed by codec A. These deviations from the pure additivity property still have to be examined in more detail. Equipment impairment factors have been introduced as a simplified measure of the perceptual effects of non-waveform codecs on the integral tran
41、smission quality from mouth to ear, for narrow-band (3003400 Hz) handset telephony. They are in no way an exact description of the effects related to each individual codec or codec tandem, which may be very diverse in their perceptual nature. Instead, they represent the relative degradation in compa
42、rison to other impairments occurring in a connection. In order to provide guidance on the quantitative amount of impairment introduced by such codecs, a framework of equipment impairment factors for the most common non-waveform codecs has been derived; Appendix I of ITU-T G.113. Its derivation is ba
43、sed on numerous subjective listening-only tests carried out in different test laboratories, so as to guarantee stable values for all the codecs under investigation so far, as well as their relations to each other. If new equipment impairment factor values for different codecs have to be derived, the
44、n the overall consistency with the established framework Rec. ITU-T P.834 (06/2015) 3 is of primary importance, so that results are obtained that are valid for network planning. The methodology described in this Recommendation was designed to fulfill this requirement. Two methodologies are currently
45、 recommended for the derivation of equipment impairment factors: this Recommendation and ITU-T P.833. The methodology described in ITU-T P.833 is based on the results of auditory listening-only tests. Consequently, equipment impairment factors derived by that methodology will reflect the incremental
46、 amount of degradation caused by the speech codec, as it is experienced by a human listener irrespective of any auditory modelling (like in ITU-T P.862), which might not be valid for all types of codecs. The approach in this Recommendation, which is based on instrumental models (so-called “objective
47、 methods“), requires that the models used provide valid estimations of auditory judgements. Only in this case the equipment-derived impairment factors will be valid. The methodology described has been tested with the model defined in ITU-T P.862, and results were found to be satisfactory in most cas
48、es; see b-ITU-T D029. Subjective tests, even if carefully designed and carried out under controlled conditions, cannot provide quality ratings that are 100 per cent reproducible under the same conditions. As a consequence, equipment impairment factors derived from one test according to the ITU-T P.8
49、33 methodology will differ to a certain extent if compared to another test. Equipment impairment factors that are derived by instrumental models are 100 per cent reproducible if the speech data and processing algorithms are precisely defined. This fact, however, does not imply a higher validity of the Ies derived according to the methodology of this Recommendation. In contrast, stable Ie values for a new codec can only be defined when the instrumental model has proven its validit
