Interaction of speech coders and atypical speech I: Effects on speech intelligibility

We investigated how standard speech coders, currently used in modern communication systems, affect the intelligibility of the speech of persons who have common speech and voice disorders. Three standardized speech coders (viz., GSM 6.10 [RPE-LTP], FS1016 [CELP], FS1015 [LPC]) and two speech coders based on subband processing were evaluated for their performance. Coder effects were assessed by measuring the intelligibility of vowels and consonants both before and after processing by the speech coders. Native English talkers who had normal hearing identified these speech sounds. Results confirmed that (a) all coders reduce the intelligibility of spoken language; (b) these effects occur in a consistent manner, with the GSM and CELP coders providing the least degradation relative to the original unprocessed speech; and (c) coders interact with individual voices so that speech is degraded differentially for different talkers.