Amplitude Compression in Hearing Aids
Amplitude compression in hearing aids should reduce too strong signals without distorting them. While the distortion of the waveform of steady-state signals is prevented, the envelope curve of rapidly changing signals is usually deformed by so-called overshoots and undershoots. During overshoots the waveform may also be distorted. The purpose of this work was to investigate if the distortion during overshoots would have a detrimental effect on the performance of the hearing aids available on the market. Intelligibility tests were performed with commercial hearing aids with amplitude compression with various values of time constants of compression, harmonic distortion, and distortion during overshoots. Ten normal hearing listeners were presented with speech from a modified rhyme test (MRT) with a signal-to-noise ratio (S/N) of -2 dB or +2 dB. An indication of a detrimental effect of the distortion during overshoots may be seen on the results at S/N = + 2 dB. Nevertheless, as the various hearing aids used in this study differ in several parameters simultaneously, a study should follow using a compression amplifier with distortion during overshoots individually controllable.
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