Subjective testing of existing and proposed communication systems is an important element of network planning and equipment design. With the evolution over the years of world telecommunications, the nature and levels of impairments experienced by system users have changed,and as a consequence, a variety of subjective testing procedures have come into existence. Discusses the technologies, communications services, and applications that support effective network strategic planning.

Because of the diversity of subjective testing methods, it is not possible, in general, to compare speech quality measurements from different laboratories. A recent experiment had the aim of determining whether comparable results can be obtained when the same test is performed in several different countries. Tape recordings of speech samples in the native languages of Britain, Canada, France, Italy, Japan, Norway, and the United States were processed by 38 communications circuits in the Communications Methods Research Department of Bell Laboratories. Recordings of the processed speech were returned to each location for evaluation, on a five-point scale, by native listeners. The communications circuits included white noise and speechmodulated noise references, pulse code modulation (PCM) references and four adaptive differential PCM (ADPCM) test circuits, with bit rates between 16 and 48 kbits/s, each with four binary error rates. An important part of the data analysis was estimation of the quality of the 16 ADPCM conditions at location B , given measurements of ADPCM quality at location A and knowledge of reference-circuit quality measured at A and at B . The subjective testing data indicate that a reasonably accurate estimate of ADPCM quality at location B is the quality measured at A adjusted by an additive constant which is the difference between average reference-circuit measurements at B and at A . The accuracy of this estimate is equivalent to that of a subjective test at location B with about seven evaluations of each transmission condition. Three physical measurements are less reliable guides to subjective quality. They lead to estimates with less accuracy than the average of three subjective ratings per circuit.

An IEEE meeting on subjective testing of voiceband codecs

Subjective Quality of the Same Speech Transmission Conditions in Seven Different Countries

Because of the diversity of testing methods, it is not possible, in general, to compare speech quality measurements from different laboratories. A recent experiment had the aim of determining whether comparable results can be obtained when the same test is performed in several different countries. Speech samples in the native languages of Britain, Canada, France, Italy, Japan, Norway and the United States were processed by 38 communications circuits at Bell Laboratories. Recordings of the processed speech were returned to each location for evaluation, on a five-point scale, by native listeners. The communications circuits included 22 references and 16 adaptive differential pcm (adpcm) test circuits. An important part of the data analysis was estimation of the quality of the 16 adpcm conditions at one location given measurements of adpcm quality elsewhere. The results indicate that a reasonably accurate estimate of adpcm quality at location B is the quality measured at A adjusted by an additive constant. The accuracy of this estimate is equivalent to that of a subjective test at location B with about seven evaluations of each transmission condition.

Subjective quality of the same speech transmission conditions in seven different countries

Digital techniques are more and more often used in telecommunications networks. How would these techniques affect the quality of transmitted speech? The use of subjective testing is generally necessary to answer this question. In this paper a degradation category rating test, which is a speech-adapted procedure of the one used for image testing, is proposed to distinguish among good telephone quality codecs. A comparative study of the sensitivity of the method and that of a classic opinion rating test is reported. It shows that the resolution of the degradation category rating test is twice that of a classic opinion rating test within good telephone quality domain. Subjective performances of various 32 kbit/s A.D.P.C.M codecs, including the effects of transmission errors and tandem connections, using degradation category rating tests are also presented.

An IEEE meeting on subjective testing of voiceband codecs

Citations

Subjective Quality of the Same Speech Transmission Conditions in Seven Different Countries

Subjective quality of the same speech transmission conditions in seven different countries

Quality evaluation of 32 kbit/s coded speech by means of degradation category ratings

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