The Intelligibility of Speech Processed by Delayed Long-Time-Averaged Compression Amplification

Abstract

Conventional compression amplification introduces undesirable distortion when brief (several milliseconds or less) time constants are utilized, and reacts too sluggishly for longer time constants. We have devised a method of processing speech in which the average power of the waveform over intervals of several tens of milliseconds is measured continuously and is used to determine the gain to be applied to the waveform at the center of each interval. The resulting amplitude-compressed signal is delayed by one-half the length of the averaging interval. Tape-recorded monosyllabic word lists are processed by a digital computer and the resulting tapes are compared with originals for intelligibility, in quiet and in noise, by hearing-impaired and by normal subjects. Preliminary results show that the intelligibility of the processed tapes is selectively superior under some conditions to that of the original tapes. [This study was supported by a grant from the Research Development Fund and by the cooperation of the Artificial Intelligence Laboratory, Stanford University.]