title: Measuring the long-term SNRs of static and adaptive compression amplification techniques for speech in noise.
abstract: 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).
  
  
  OBJECTIVE
  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.
  
  
  METHODS
  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.
authors.affiliation: Institute of Biomedical Engineering, National Yang-Ming University, Taipei, Taiwan.
authors.forename: Ying-Hui
authors.initials: YH
authors.lastname: Lai
authors.forename: Pei-Chun
authors.initials: PC
authors.lastname: Li
authors.forename: Kuen-Shian
authors.initials: KS
authors.lastname: Tsai
authors.forename: Woei-Chyn
authors.initials: WC
authors.lastname: Chu
authors.forename: Shuenn-Tsong
authors.initials: ST
authors.lastname: Young
mesh_terms: D001309:Auditory Threshold; D004867:Equipment Design; D005500:Follow-Up Studies; D006310:Hearing Aids / Q000592:standards*; D006316:Hearing Loss, High-Frequency / Q000503:physiopathology* / Q000534:rehabilitation; D006319:Hearing Loss, Sensorineural / Q000503:physiopathology* / Q000534:rehabilitation; D006801:Humans; D013067:Speech Perception / Q000502:physiology*; D013997:Time Factors