The role of modulation characteristics on the interaction between hearing aid compression and signal-to-noise ratio

Abstract

Hearing aids use compression amplification to provide greater gain to lower amplitude sounds than higher amplitude sounds. When there are two signals (i.e., speech-in-noise) hearing aids alter the signal-to-noise ratio (SNR) by disproportionately increasing the lower amplitude signal compared to the higher amplitude signal. The purpose of the present study was to examine the relationship between hearing aid compression and SNR alteration along a continuum of signal modulation characteristics. Sentence stimuli were combined with either 1-, 2-, or 6-talker modulated noise at a range of SNRs. Speech-in-noise signals were processed at a range of reverberation times with the speech and noise signals co-located. Stimuli were then processed at a range of compression release times (RT) using a hearing aid simulation which mimicked six-channel hearing aid processing. Signals were acoustically analyzed using a digital inversion method which employed phase cancellation to separate speech and noise signals at the output of the compressor. This enabled us to quantify changes to SNR as a result of compression. Results indicated that shorter RTs altered SNR more than longer RTs; however, reverberation reduced or eliminated the differences among RTs. Additionally, less modulated maskers lead to poorer output SNRs than modulated maskers. [Work supported by NIH.]