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14、TIA WITHOUT SUCH LIMITATIONS. TIA/EIA-102.BABBTable of Contents1. Introduction . 11.1 Scope 11.2 Overview 22. Revision History 33. References . 44. Definitions. 55. Speech Data Bases. 65.1 Speech Data Base Requirements 75.2 Speech Data Base Reference Conditions . 75.3 Speech Data Base for MOS Test 7
15、6. Production of Digital Vocoder Recorded Tapes . 106.1 Equipment List . 106.2 Vocoder Test Platform Operation Check . 106.3 Test Setup. 116.3.1 Audio Levels . 126.3.2 Channel Error Randomizer 126.4 Vocoder Testing . 136.4.1 Vocoder Setup. 136.4.2 System Reset . 136.4.3 Channel Error Test 146.4.4 Re
16、duced Level Input Test 146.4.5 Clean Channel Test . 146.4.6 Reference Processing 147. Subjective Evaluation of Speech Quality 157.1 Stimulus Recording Preparation. 157.1.1 Experiment Randomization. 157.2 MOS Evaluation Laboratory 177.3 Transmission Quality Testing 177.3.1 Conducting the MOS Listenin
17、g Test. 187.4 Reporting of Results. 198. MOS Result Analysis 218.1 ANOVA Calculation 218.2 Newman-Keuls Analysis 279. Disclosure of MOS Test Result. 36Annex A. Tables. 39Annex B. Vocoder Test Platform Description . 51Annex C. C Source Files 58TIA/EIA/102.BABBiiThis page intentionally left blank.TIA/
18、EIA/102.BABB11. IntroductionThis standard details definitions and methods of measurement for testing conformance ofspeech codecs used in Project 25 Digital Land Mobile Radio Equipment to the referencespeech codec defined for Project 25. The Project 25 speech codec is defined in Project25 Vocoder Des
19、cription, TIA-102.BABA, reference 13. The purpose of this standard isto assure that a speech codec in any given piece of Project 25 Equipment is compliantwith TIA-102.BABA.Section 5 will discuss the speech data base that was chosen to be used in the vocodertesting and comparison. Section 6 contains
20、the details of the vocoder testing as well asthe speech data base used for the testing. Section 7 discusses the design of the listeningtests themselves. Section 8 discusses the overall evaluation procedure of the vocodercombinations. Section 9 describes the disclosure of the MOS test results. Lastly
21、, anannex is included which contains additional detail.1.1 ScopeThis document specifies the procedures to be employed to test that implementations ofTIA-102.BABA compatible speech codecs comply with the standard. This speech codecis the Improved Multi-Band Excitation (IMBETM, a trademark of Digital
22、Voice SystemsInc.) system described in TIA-102.BABA, Project 25 Vocoder Description. The IMBEspeech codec is used to digitally encode the speech signal and provide forward errorcontrol for transmission at a data rate of 7200 b/s.The need for this standard arises from the fact that implementations of
23、 speech coders donot need to have identical numerical precision in the internal arithmetic operations to becompatible. Since individual designers implement algorithms in different manners, it isnot possible to create a standard set of test vectors to assess conformance to a standard.This document de
24、scribes a series of tests that are used to test conformance to thespecification. These tests do not necessarily ensure that the speech codecs operatesatisfactorily under all possible input signals and it is still a requirement of themanufacturer to ensure that his implementation operates in a consis
25、tent manner. Thepurpose of these tests is to test for standard compliance. The manufacturer is encouragedto provide the highest possible performance but it is not the purpose of these tests todetermine that performance.The testing of the codecs is based upon subjective tests which employ listening t
26、ests tojudge overall speech quality.This standard takes the approach of defining a reference speech codec and then eachmanufacturer tests his implementation relative to the reference. All possiblecombinations of test codec to reference codec are evaluated. The reference speech codecis based upon the
27、 Digital Voice Systems Incorporated implementation of the IMBEalgorithm on the VC-20 Project 25 hardware card.TIA/EIA/102.BABB2Reference (VC-20)Reference (VC-20)Vocoder Under TestVocoder Under TestEncoders DecodersAudio SourceAudio ComparisonFour CombinationsFigure 1-1 Encoder and Decoder Test Combi
28、nations1.2 OverviewThe way that the implementation of the speech coder is tested is by comparing it with astandardized reference implementation. The test works by interoperating the testedvocoder with the reference in all combinations of encode and decode pairs, to verify thataudio is encoded and de
29、coded such that listeners perceive little difference. Thesecombinations of speech coder pairs are diagrammed in figure 1-1.The audio quality of each combination of encoder and decoder is subjectively rated.These ratings are then compared with each other to determine if they are statisticallyequivale
30、nt. The vocoder under test passes the test if the ratings show no significantstatistical variation.The speech quality performance issue is difficult to quantify since it is a subjective issue.There is no known objective measurement that can be performed to rate the acceptabilityof the speech coder p
31、erformance to a human listener. Because of this the performanceevaluation must rely upon subjective testing. The subjective testing involves the use of apanel of listeners who rate the vocoders performance on a 5 point scale. Since opinionsof listeners will vary, the result from a number of listener
32、s is obtained and averaged toobtain an overall score.To evaluate the overall speech quality it is necessary to conduct an experiment in acontrolled manner so that unintentional variation in the scoring is avoided. The purposeof the testing is to determine differences in performance among the differe
33、nt vocodercombinations. The confidence we have that any apparent differences in performance aredue to random statistical variation and not vocoder defects will depend upon how well weprevent differences from occurring in the testing of the various vocoder combinations. Inaddition, the judgment as to
34、 the effect of various impairments upon the vocodercombinations will depend upon how well the introduction of those impairments iscontrolled. The statistical controls for the experiment are given in section 7.The listening test also evaluates the vocoder combinations under a variety of testcondition
35、s. The test conditions were chosen to be representative of those expected to beexperienced in a land mobile radio environment. The test is organized so that each testcondition tests only one aspect of system performance. Hence only a limited number ofoperating conditions are tested. To test all poss
36、ible operating conditions would lead to atest that would be too unwieldy to conduct. The operation of the vocoder with variouschannel impairments, various talkers and speaking volumes is determined through the useof a Mean Opinion Score (MOS) test.The vocoder implementations are electrically interco
37、nnected through a device that isintended to provide the standardized test conditions given above. This device is calledTIA/EIA/102.BABB3the Vocoder Test Platform. A detailed description is given in Annex B. A block diagramof how the Vocoder Test Platform interconnects the vocoders is given in figure
38、 1-2. Theuse of the Test Platform for testing is given in detail in section 6.Voice EncoderVoice Decoderi0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0
39、i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0i0Source AudioOutput AudioVocoder Test PlatformEIA-422 InterfacesFigure 1-2 Vocoder Test Platform Audio FlowThe overall plan of the test for the vocoder is outlined in figure 1-3. The test
40、 begins withthe source audio material. There are several conditions that the source material mustsatisfy, and these are covered in section 5. The source audio material is then passedthrough the vocoder test platform and the different vocoder combinations, with differenttest conditions, to produce a
41、recording of output audio. This procedure is given in section6. The output audio is then randomized in order, and commingled with audio that hascalibrated noise, i.e., Modulated Noise Reference Units (MNRUs) to provide samplessuitable for a listening test. The MNRU audio is also processed by the Voc
42、oder TestPlatform. The randomization step, together with the listening test, is described in section7. The listening step then produces MOS scores, which are statistically analyzed forvariations that are beyond the random expected variations in such an experiment. Thisanalysis is described in sectio
43、n 8. The result of the test is then presented in section 9,which describes a spreadsheet for this analysis.Get Source Audio Material.(section 5)Use the Vocoder Test Platform to test the vocoderimplementation under various test conditions.Also process the MNRU material with the Test Platform.(section
44、 6)Randomize the order of the Output Audio samples.(section 7)Conduct a Listening Test of the audio samples to getMOS results.(section 7)Statistically analyze the MOS results to detect anyexcessive variations.(section 8)TIA/EIA/102.BABB4Present the results in a spreadsheet.(section 9)Figure 1-3 MOS
45、Test Plan2. Revision HistoryVersion 0.0, 22 June 1995, initial version of the document.Version 1.0, 27 October 1995, incorporates numerous comments.Version 2.0, 10 May 1996, adjusted levels, added test software in Annex C.Version 2.1, 18 June 1996, added brief description of source material recordin
46、g.Version 2.2, 24 September 1996, modified ANOVA and N-K tables from letter ballot.TIA/EIA/102.BABB53. References1 IEEE Subcommittee on Subjective Measurements, “IEEE Speech Quality MeasureRecommendation“, IEEE Trans. on Audio RADC-TR-85-46, March 1985.3 J.D. Tardelli, J. LeBlanc and P. Gatewood, “R
47、ADC/EEV Diagnostic Rhyme TestSystem Improvements“, Chapter 8. “DRT/DAM Mastering Program“, Appendix A“DRT/DAM Master Library“; RADC-TR-89-256, November 1989.4 W.D. Voiers “Diagnostic Acceptability Measure for Speech CommunicationSystems“, Proc. 1977 IEEE ICASSP, Hartford, CN. pp 204-207, May 1977.5
48、S.R. Quackenbush, T.P. Barnwell and M.A. Clements, Objective Measures ofSpeech Quality, Prentice Hall, Englewood Cliffs, NJ, 1988. ISBN 0-13-629056-6.6 J.T. Sims and J.D. Tardelli, “The Effects of Controlled Speech Level Input on theIntelligibility Testing of Speech Compression Algorithms“, Proc. of
49、 1985 IEEEICASSP, pp. 430-433.7 J.T. Sims, “A Speech-To-Noise Ratio Measurement Algorithm“, JASA, V78, Num.5, pp. 1671-1674, 1985.8 P.T. Brady, “Equivalent Peak Level: A Threshold-Independent Speech-LevelMeasure“, JASA, V44, pp. 695-699, 1968.9 G.F. Sandy and J.E. Parker, “Digital Voice Processor Consortium Final ReportAPPENDIX A“, MITRE Corp. MTR-84W00053-02, McLean, VA, March 1982.10 CCITT “Telephone Transmission Quality“, Blue Book, series P recommendations,Volume V, Rec. P.81, pages 198ff.11 CCITT “Telephone Transmission Quality“, Blue Book, series P recomme
