Factors influencing ratings of speech naturalness in augmentative and alternative communication

The concept of speech naturalness has been used in the field of speech-language pathology as a clinical measure of perceptual quality of “normal” and “not normal” speech. Whereas measures of intelligibility have been commonly used to assess the quality of voice output augmentative and alternative communication (AAC) devices using DECTalk™ speech, measures of speech naturalness have not. Three studies were conducted to determine the effects of manipulation of rate, pitch, and pause on ratings of speech naturalness by naive listeners of DECTalk synthetic speech. The results indicate that DECTalk speech characterized by faster rate and no added pauses was perceived as being more natural than speech with slow rate and added pauses. Manipulation of pitch had no effect on naturalness ratings.