Background: Multichannel wide-dynamic-range compression (WDRC) is a widely adopted amplification
scheme in modern digital hearing aids. It attempts to provide individuals with loudness
recruitment with superior speech intelligibility and greater listening comfort over
a wider range of input levels. However, recent surveys have shown that compression
processing (operating in the nonlinear regime) usually reduces the long-term signal-to-noise
ratio (SNR).
Purpose: The purpose of this study was to determine the long-term SNR in an adaptive compression-ratio
(CR) amplification scheme called adaptive wide-dynamic-range compression (AWDRC),
and to determine whether this concept is better than static WDRC amplification at
improving the long-term SNR for speech in noise.
Design and Study Sample: AWDRC uses the input short-term dynamic range to adjust the CR to maximize audibility
and comfort. Various methods for evaluating the long-term SNR were used to observe
the relationship between the CR and output SNR performance in AWDRC for seven typical
audiograms, and to compare the results with those for static WDRC amplification.
Results: The results showed that the variation of the CR in AWDRC amplification can maintain
the comfort and audibility of the output sound. In addition, the average long-term
SNR improved by 0.1–5.5 dB for a flat hearing loss, by 0.2–3.4 dB for a reverse sloping
hearing loss, by 1.4–4.8 dB for a high-frequency hearing loss, and by 0.3–5.7 dB for
a mild-to-moderate-sloping high-frequency hearing loss relative to static WDRC amplification.
The output long-term SNR differed significantly (p < .001) between static WDRC and AWDRC amplification.
Conclusions: The results of this study show that AWDRC, which uses the characteristics of the
input signal to adaptively adjust the CR, provides better long-term SNR performance
than static WDRC amplification.
Key Words
Hearing aids - adaptive compression amplification - long-term SNR - AWDRC