Digital audio gain control for hearing aids

It is suggested that the digital realization of an audio gain controller can bypass some of the problems commonly encountered with analog hearing aid automatic gain controllers, such as accurate setting of its input/output state characteristic (SC). The author describes the embedding of a digital audio gain controller in a TMS32010 DSP (digital signal processor). Its SC is graphically programmable to any desired shape, and its dynamic characteristics are controlled by the input instant envelope. The latter is obtained by nonlinear filtering (demodulation through log conversion). It is shown that this method avoids overshoots and high-to-low level masking while minimizing waveform distortion