The effects of compression ratio and release-time on loud speech and noise signals, processed by a simulated non-linear hearing aid
Erik M. Schmidt · Proceedings of the International Symposium on Auditory and Audiological Research · 2007
This study investigated the effect of compression ratio and release time on hearing aid wearers’ impressions of loud input signals. Two speech and noise signals, differing in spectra and signal-to-noise ratio, were processed in a model compressor with sixteen combinations of compression ratio and release time. The RMS input level of the signals was 75 dB SPL. Subjects rated the processed signals on categorical scales, in regard to loudness, speech clarity, noisiness and overall acceptance. With a compression ratio between 1.5:1 and 2:1 and a release time of 4000-ms, the highest degree of speech clarity and the lowest possible noisiness was achieved, while still maintaining a positive rating on the acceptance-scale. When shorter release times of 40 and 400-ms were used, ratings of acceptance declined when the compression ratio was 3:1 or greater. Thus, the preferred setting appears to be long release times in combination with a low compression ratio - providing the listener with a realistic loudness for the signal. When faster regulation is needed the compression ratio should not exceed 3:1.