Difference limen for amplitude compression of speech

It is postulated that the amount of information carried by speech can be altered by speech modifications which can be perceived aurally. Therefore, amplitude compression might increase intelligibility if a reduction of level differences between strong and weak speech sound is perceivable. Difference limen for attack (TA) and release (TR) times of compression for various compression ratios (CR's) based on a quality change was determined by the adjustment or ABX methods. A 1.7-s-long utterance with approximately constant maximal rms levels of words was submitted to wide-band compression. Masking noise added after compression at −10 dB (re speech) equalized the noise background for various conditions. The smaller the CR or the TA, the shorter the TR had to be to provide a perceptible change in quality; e.g., experienced normally hearing subjects needed TR equal to or smaller than 420 and 250 ms to discriminate a quality change when CR = 5 and TA equal to 10 and 3 ms, respectively, from linear amplification. Naive normally hearing listeners needed a much shorter TR (between 30 and 40 ms for the same conditions). Testing of hearing impaired listeners is presently in progress. [Work supported by NIH NS 12946.]