Effects of single-band syllabic amplitude compression on temporal speech information in nonsense syllables and in sentences.

Abstract

The effects of single-band amplitude compression on the use by subjects with normal hearing of temporal speech information were assessed using speech stimuli that had been processed to remove most spectral information before being compressed. The resulting signal-related-noise (SRN) stimuli isolated the effects of compression on the temporal information in speech by making it impossible for subjects to identify stimulus items on the basis of spectral speech information. Subjects with normal hearing listened to /aCa/ SRN disyllables that had been subjected to single-band compression at various combinations of compression ratio (CR) and time constants (TC). Performance was reduced only in the most severe compression condition (CR = 8; TC = 50), and then only slightly. Additional testing showed that subjects could use both periodicity and compression-overshoot artifactual information--in addition to envelope information--to identify the compressed /aCa/ stimuli. When a list of 10 context-controlled sentences was converted to SRN and compressed at CR = 8 and TC = 50, the ability of subjects with normal hearing to identify the sentences was significantly affected. Results established that (a) subjects with normal hearing differ widely in their abilities to use temporal information for speech identification, even after training; (b) subjects can learn to use both temporal envelope and periodicity information for identification if disyllables, even though; (c) subjects with normal hearing need envelope but not periodicity information to identify SRN sentences in a closed set. These results suggest that single-band compression at CR = 8 and TC = 50 would be undesirable for persons with limited ability to resolve speech spectral information. It is currently not known how less severe compression conditions would affect envelope information in sentences.