EFFECTS OF SINGLE-BAND SYLLABIC AMPLITUDE COMPRESSION ON TEMPORAL SPEECH INFORMATION IN NONSENSE SYLLABLES AND IN SENTENCES

The effects oi single-band amplitude compression on the use by subject s with normal hearing of temporal speech information were assessed usi ng speech stimuli that had been processed to remove most spectral info rmation before being compressed. The resulting signal-related-noise (S RN) stimuli isolated the effects of compression on the temporal inform ation in speech by making ii: impossible for subjects to identify stim ulus items on the basis of speciral speech information. Subjects with normal hearing listened to /aCa/ SRN disyllables that had been subject ed to single-band compression at various combinations of compression r atio (GR) and time constants (TC). Performance was reduced only in the most severe compression condition (CR = 8; TC = 50), and then only sl ightly. Additional testing showed that subjects could use both periodi city and compression-overshoot artifactual information-in addition to envelope information-to identify the compressed /aCa/ stimuli. When a list of IO context-controlled sentences was converted to SRN and compr essed at GR = 8 and TC = 50, the ability of subjects with normal heari ng to identify the sentences was significantly affected. Results estab lished that (a) subjects with normal hearing differ widely in their ab ilities to use temporal information for speech identification, even af ter training; (b) subjects can learn to use both temporal Envelope and periodicity information for identification of disyllables, even thoug h; (c) subjects with normal hearing need envelope but not periodicity information to identify SRN sentences in a closed set. These results s uggest that single-band compression at CR = 8 and TC = 50 would be und esirable for persons with limited ability to resolve speech spectral i nformation. it is currently not known how less severe compression cond itions would affect envelope information in sentences.