Effects of compression on the use of onset time differences to detect one tone in the presence of another

It is easier to hear one of two notionally "simultaneous" tone complexes if the onset of the masker complex is delayed relative to that of the signal. However, the ability to use onset asynchrony as a cue may be reduced when using amplitude compression, due to distortion of the onset of sounds (overshoot effects). We assessed how fast- and slow-acting five-channel compression affects the ability to use onset asynchrony to detect one (signal) complex tone when another (masking) complex tone is played almost simultaneously. A 2: 1 compression ratio was used with normal-hearing subjects and individual compression ratios and gains recommended by the CAM2 hearing aid fitting method were used for hearing-impaired subjects. For the normal-hearing subjects, performance improved with increasing onset asynchrony in all conditions. The improvement was greatest with fast compression and least with no compression. Preliminary results for the hearing-impaired subjects indicate smaller but similar effects of onset asynchrony and a greater benefit of compression. The benefit of compression probably occurs because compression increases the level of the part of the signal that occurs before the masker relative to the masker.