Design and evaluation of a two-channel compression hearing aid.

The design of a two-channel compression hearing aid for persons with moderate sensorineural hearing losses with recruitment is described. The aid applies slow-acting automatic gain control (AGC) to the whole signal, and then splits the signal into two bands, with separate fast-acting (syllabic) AGC in each band. Trials evaluating the aid have shown that it allows speech in quiet to be understood over a wide range of sound levels without any need to adjust the controls on the aid. It also gives speech intelligibility in noise superior to that allowed by a comparable linear (non-compression) aid, a comparable single-channel compression aid, and by unaided listening. Pilot experiments comparing two different methods for fitting the aid suggest that fitting using speech as the test signal is superior to fitting using narrow band tonal signals.