Speech quality evaluation using "phoneme-specific" sentences

A new approach is described for the design of speech materials used in subjective speech quality evaluation. Speech sounds are classified by their acoustic properties, and sentences are composed so as to concentrate all sounds with similar properties within one sentence. As a test of the method, subjective quality data were collected, using both a rank ordering and a rating task, from a set of 12 linear predictive vocoders, whose parameters were chosen so as to equate their bit rates at 2600 bps. The results show that the method can reliably reveal small differences in quality, and also yields information that can be of diagnostic help in determining the causes of quality degradation by a particular vocoder. A set of phoneme-specific sentences is appended.