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.807 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (02/2016) SERIES P: TERMINALS AND SUBJECTIVE AND OBJECTIVE ASSESSMENT METHODS Methods for objective and subjective assessment of speech quality Subjective test methodolo
2、gy for assessing speech intelligibility Recommendation ITU-T P.807 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
3、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.800 Audiovisual quality i
4、n 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 analysis, evaluation and
5、 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.807 (02/2016) i Recommendation ITU-T P.807 S
6、ubjective test methodology for assessing speech intelligibility Summary Recommendation ITU-T P.807 describes a subjective testing methodology for assessing speech intelligibility in communications settings, systems and devices. The method provides a percent correct intelligibility score based on a t
7、wo-alternative, forced-choice task where the stimulus is one of the two words from a pair of words, i.e., a test item. Half of the test items are rhyming word-pairs (i.e., they differ only in the initial consonant) and half are alliterative word-pairs (i.e., they differ only in the final consonant).
8、 The two critical consonants in each test item differ only in a single distinctive feature (see Annex A for a description of distinctive features). In addition to a score for overall intelligibility, the method provides scores for each of six distinctive features: voicing, nasality, sustention, sibi
9、lation, graveness and compactness. These scores may be used to diagnose the specific cause of impairments leading to degradation of speech intelligibility. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T P.807 2016-02-29 12 11.1002/1000/12750 Keywords Diagnostic assessment o
10、f intelligibility, distinctive features, speech intelligibility testing. * 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.80
11、7 (02/2016) FOREWORD 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 responsi
12、ble 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 Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-
13、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 information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative
14、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 agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandat
15、ory 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 other obligatory language such as “must“ and the negative equivalents are used to express requirements. The
16、 use of such words 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
17、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 process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property
18、, 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 strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2016 All rights reserved. No
19、 part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T P.807 (02/2016) iii Table of Contents Page 1 Scope . 1 2 References . 1 3 Definitions 1 3.1 Terms defined elsewhere 1 3.2 Terms defined in this Recommendation . 1 4 Abbreviat
20、ions and acronyms 2 5 Conventions 2 6 Description of the ITU-T P.807 testing methodology 2 6.1 Need for an ITU-T intelligibility testing method . 2 6.2 Rhyme tests 3 6.3 Intelligibility test method ITU-T P.807 . 4 6.4 ITU-T P.807 test results . 6 Annex A ITU-T P.807 and distinctive features 12 Appen
21、dix I Example instructions for the ITU-T P.807 test 14 Bibliography. 17 Rec. ITU-T P.807 (02/2016) 1 Recommendation ITU-T P.807 Subjective test methodology for assessing speech intelligibility 1 Scope This Recommendation describes a subjective testing methodology for assessing speech intelligibility
22、 in communications settings, systems and devices. The ITU-T P.807 test methodology has been tested and was found to be appropriate for assessing speech intelligibility of telecommunications systems (e.g., speech codecs), including channel impairments and background noise conditions and for terminals
23、 and devices (e.g., handsets, intercom systems). It is designed for use with naive subjects and requires little in the way of specialized equipment or software. The method applies to word intelligibility and does not address intelligibility of phrases or sentences. The method described here applies
24、to North American English. However, the method could be adapted to other languages or dialects taking into account the appropriate set of distinctive features for the language. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this t
25、ext, 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 edition
26、 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 P.800 Recommendation ITU-T
27、P.800 (1996), Methods for subjective determination of transmission quality. 3 Definitions 3.1 Terms defined elsewhere None. 3.2 Terms defined in this Recommendation This Recommendation defines the following terms: 3.2.1 compactness: Distinctive feature that distinguishes compact phonemes from diffus
28、e phonemes. Compact phonemes are produced by constriction toward the rear of the vocal tract; diffuse phonemes by constriction near the middle. Compact phonemes are characterized by the concentration of spectral energy in the mid-frequency range; diffuse phonemes by the distribution of energy over m
29、ore-widely separated spectral peaks. 3.2.2 graveness: Distinctive feature that distinguishes grave phonemes from acute phonemes. Grave phonemes are produced by constriction toward the anterior of the vocal tract; acute by constriction in the middle of the tract. Grave phonemes are distinguished amon
30、g other things by the origin and direction of second-formant transitions. Grave consonants always involve relatively steep upward transitions of the second formant. Acute consonants usually involve downward second-formant transitions, depending on vowel environment and the phoneme involved. In gener
31、al, grave phonemes are characterized by greater concentration of low-frequency spectral energy than are acute phonemes. 2 Rec. ITU-T P.807 (02/2016) 3.2.3 nasality: Distinctive feature that distinguishes nasal phonemes from non-nasal phonemes. Nasals are produced by lowering of the velum, allowing a
32、ir to escape through the nasal passages; non-nasals by closing the nasal passages. Nasal phonemes are distinguished by relatively pronounced resonances at circa 200, 800, and 2200 Hz and by the presence of nulls throughout the frequency range. 3.2.4 sibilation: Distinctive feature that distinguishes
33、 sibilated phonemes from non-sibilated phonemes. Sibilants involve extreme constriction of the vocal tract that produces turbulence and high-frequency noise. Sibilant consonants are characterized by higher-frequency noise and greater duration than their non-sibilant counterparts. 3.2.5 sustention: D
34、istinctive feature that distinguishes sustained phonemes from interrupted phonemes. Sustained phonemes are produced by incomplete constriction of the vocal tract; interrupted phonemes by complete constriction of the tract at some point. Sustained phonemes are distinguished by their gradual onset and
35、 by the presence of mid-frequency noise, interrupted by their abrupt onset. Sustained phonemes have characteristic durational and high-frequency cues that distinguish them from their interrupted counterparts. 3.2.6 voicing: Distinctive feature that distinguishes voiced phonemes from unvoiced phoneme
36、s. Voiced phonemes involve free vibration of the vocal cords; unvoiced phonemes do not. Voiced phonemes are distinguished from their unvoiced counterparts, or cognates, by the presence of periodicity, and, in particular, by the time of onset in periodicity. In voiced consonants, preceding vowels ten
37、d to be of greater duration than in the case of unvoiced consonants. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: 2AFC 2-Alternative, Forced-Choice ACR Absolute Category Rating AMR-WB Adaptive Multirate Codec Wideband ANSI American National Standard
38、s Institute DALT Diagnostic Alliteration Test DRT Diagnostic Rhyme Test HATS Head And Torso Simulator IPA International Phonetic Alphabet MOS Mean Opinion Score MRT Modified Rhyme Test RF Radio Frequency SNR Signal to Noise Ratio 5 Conventions None. 6 Description of the ITU-T P.807 testing methodolo
39、gy 6.1 Need for an ITU-T intelligibility testing method In recent years, there has been increased interest in testing systems or devices for intelligibility. This is especially relevant for “speech enhancement“ techniques and algorithms, e.g., noise Rec. ITU-T P.807 (02/2016) 3 reduction and bandwid
40、th extension, where subjective evaluation has concentrated on speech quality and little is known about the effects of such algorithms on speech intelligibility. The purpose of this Recommendation is to provide such a method. Most of the subjective testing methodologies, standardized under ITU-T Stud
41、y Group 12 (SG12), involve the use of relatively large panels of naive listeners, typically a minimum of 32 subjects. This practice has several advantages: 1) there is no need for extensive selection or training of test subjects and 2) the test results can be generalized to the general population of
42、 users of the communication systems being tested. The American National Standards Institute (ANSI) standard S3.2 b-ANSI specifies that the diagnostic rhyme test (DRT) and modified rhyme test (MRT) use small panels of highly trained and motivated expert listeners to provide stable and reliable result
43、s. This has led to the use of panels of eight or fewer test subjects. For practical purposes, this has limited these methods to the relatively few test laboratories that can maintain a panel of trained listeners for routine intelligibility testing. In addition to the methods that use individual word
44、s as stimuli, there are a number of test methods that use longer segments of speech (phrases or sentences) as the test stimuli. These methods have often been deemed impractical for routine testing. The primary criticisms are that sentence-based intelligibility tests are inefficient. The duration of
45、a trial for such longer stimuli, limits the data collection rate to ten or fewer responses per minute of testing, whereas the use of single word-stimuli can raise that response rate by a factor of three. Furthermore, sentence tests typically have little control for the effects of context. With singl
46、e-word stimuli, there is no context, so context cannot be a confounding factor. 6.2 Rhyme tests The two most widely used intelligibility tests, the MRT b-House and the DRT b-Voiers, are described in ANSI standard S3.2 b-ANSI. Both of these test methods use single syllable stimuli in a multiple-choic
47、e task, six choices for the MRT and two choices for the DRT. Both methods express their intelligibility scores in terms of percent correct adjusted for chance (i.e., adjusted for guessing). The MRT is a test of consonant discrimination in both the initial (rhyming) and the final (alliterative) posit
48、ions in single-syllable words while the DRT only tests consonants in the initial position. There is, however, a derivative of the DRT that uses the same principles and structure as the DRT, but tests final consonants, i.e., the diagnostic alliteration test (DALT). The approach used here is a combina
49、tion of DRT items and DALT items to test both initial and final consonants. Each MRT item includes six response alternatives where the relevant consonants of those alternatives can differ in one to six distinctive features. An analysis of discrimination errors in the results of Miller-Nicely b-Miller shows that a vast majority of errors in consonant discrimination occur for single distinctive-feature oppositions. Furthermore, the error rate decreases monotonically with increases in the number of distinctive-feature differences. This finding suggests that th
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