In recent years, the problem of measuring the subjective quality of processed speech has been given considerable attention. One motivation for this interest is the need for test procedures that can provide valid and reliable measures of the performance of speech-communication systems. It has long been recognized that a high level of speech intelligibility, as measured with conventional word- or sentence-intelligibility tests, is a necessary but hardly sufficient condition for effective communication and user acceptance of a system. Nevertheless, there has been little progress in the development of suitable test procedures that measure attributes of speech other than intelligibility. this survey of presently available methods for measuring such attributes will attempt to illustrate the various difficulties that are encountered in dealing with the concept of speech quality. Some of these difficulties can probably be traced to the fact that speech-quality measures, in contrast to intelligibility measures, are not based on -right- and -wrong- listener responses. Rather, listeners make speech-quality judgements along one or more psychological continua. Because of the nature of the problem to be discussed, this survey cannot be exhaustive.
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