Programmable master hearing aid with adaptive noise reduction using a TMS320-20
Norbert Dillier · 2003
A TMS320-20-based coprocessor in a PDP 11/73 was chosen as key element of a programmable digital master hearing aid. The system includes 16-bit A/D (analog-to-digital) and D/A with antialiasing filters, programmable attenuators, and a touch-screen terminal for patient interaction. A multiband compression table with amplitude correction factors for 64 frequency bands is generated from estimated loudness growth or isoloudness functions of hearing-aid candidates and transferred via DMA (direct memory access) into the TMS320-20 data RAM. Processing steps for input signals include A/D-conversion at 10 kHz, radix-4-FFT (fast Fourier transform) frequency-dependent amplitude spectrum modification, inverse FFT, windowed overlap-add, D/A-conversion. Prior to amplitude compression, the amplitude spectrum may be modified by an adaptive pseudocepstrum noise-reduction algorithm.>