Auditory perceptual efficacy of nonlinear frequency compression used in hearing aids: A review

Abstract

Many patients with sensorineural hearing loss have a precipitous high-frequency loss with relatively good thresholds in the low frequencies. This present paper briefly introduces and compares the basic principles of four types of frequency lowering algorithms with emphasis on nonlinear frequency compression (NLFC). A review of the effects of the NLFC algorithm on speech and music perception and sound quality appraisal is then provided. For vowel perception, it seems that the benefits provided by NLFC are limited, which are probably related to the parameter settings of the compression. For consonant perception, several studies have shown that NLFC provides improved perception of high-frequency consonants such as /s/ and /z/. However, a few other studies have demonstrated negative results in consonant perception. In terms of sentence recognition, persistent use of NLFC might provide improved performance. Compared to the conventional processing, NLFC does not alter the speech sound quality appraisal and music perception as long as the compression setting is not too aggressive. In the subsequent section, the relevant factors with regard to NLFC settings, time-course of acclimatization, listener characteristics, and perceptual tasks are discussed. Although the literature shows mixed results on the perceptual efficacy of NLFC, this technique improved certain aspects of speech understanding in certain hearing-impaired listeners. Little research is available on speech perception outcomes in languages other than English. More clinical data are needed to verify the perceptual efficacy of NLFC in patients with precipitous high-frequency hearing loss. Such knowledge will help guide clinical rehabilitation of those patients.

Effects of nonlinear frequency compression on the acoustic properties and recognition of speech sounds in Mandarin Chinese

“…To help hearing-impaired individuals gain audibility to a wider range of acoustical information, a diversity of hearing aid techniques have been proposed and implemented (see Simpson, 2009;Simpson et al, 2017;Mao et al, 2017). Contemporary frequency-lowering techniques are designed to bring high-frequency information to low-frequency regions so that the inaudible speech information becomes accessible to the hearing-impaired listeners.…”

“…Among the studies on NLFC, there are multiple factors that may account for the individual variability and inconsistent results in the recognition of frequency-lowered speech (Mao et al, 2017). Researchers identified two types of resources: intrinsic and extrinsic factors (Alexander, 2013).…”

Speech Perception and Sound-Quality Rating with an Adaptive Nonlinear Frequency Compression Algorithm in Mandarin-Speaking Hearing Aid Users

“…Frequency lowering, a signal-processing technique that essentially shifts inaudible high-frequency information to the audible lower-frequency region, has been widely used in hearing aids to help hearing-impaired listeners gain accessibility to the linguistic information contained in the highfrequency region (see Simpson, 1 Mao et al, 2 and Simpson et al 3 for reviews). Among the various types of frequencylowering techniques, nonlinear frequency compression (NLFC) has drawn a great deal of attention from hearing aid research community.…”

“…Among the various types of frequencylowering techniques, nonlinear frequency compression (NLFC) has drawn a great deal of attention from hearing aid research community. 1,2 In contrast to linear frequency compression, where all frequency components are lowered by a constant factor, the NLFC algorithm uses a predefined cut-off frequency (CT) and compression ratio (CR) such that all input signals above the CT are compressed into the output frequency area that is between the CT and the maximum output frequency of the NLFC algorithm. Higher frequencies above the CT are compressed in greater amounts than lower frequencies above the CT.…”

“…As reviewed in Mao et al, 2 Simpson et al, 3 and Akinseye et al, 10 there have been several studies evaluating the efficacy of NLFC with different parameter settings on speech perception in hearing-impaired listeners (e.g., Alexander and Rallapalli, 6 Brennan et al, 11 Ching et al, 12 Glista et al, 13 Wolfe et al, [14][15][16] Wright et al, 17 McCreery et al, 31 Hopkins et al 32 ). Only a few studies provided data regarding speech perception of English-speaking hearing-impaired people using adaptive NLFC-fitted hearing devices with different parameter settings, which might be because the adaptive NLFC is a newly developed algorithm and has not been widely adopted yet.…”