Interactions between speech coders and disordered speech

We examined the impact of standard speech coders currently used in modern communication systems, on the quality of speech from persons with common speech and voice disorders. Four standardized coders, viz. G. 728 LD-CELP, GSM 6.10 RPE-LTP, FS1016 CELP, FS1015 LPC and the recently proposed US Federal Standard 2400 bps MELP were evaluated with speech samples collected from 30 disordered talkers. Objective speech quality measures, including the auditory distance parameter based on the measuring normalizing blocks technique, and the perceptual speech quality measure, and subjective impressions of speech coder performance were used to assess the interaction between speech coder and speech disorder. Objective speech quality measures revealed that the performance of the LD-CELP and GSM RPE-LTP coders was not measurably influenced by the type of input speech, and that MELP, FS1015 LPC and to a certain extent FS1016 CELP exhibited degraded performance with speech samples from disordered talkers. Results from perceptual experiments were in contrast with the objective measures of speech quality; ratings of speech coder performance indicated that the listeners are less sensitive to coder-induced distortions with abnormal speech samples.