Abstract
BackgroundRecently two major manufacturers of hearing aids introduced two distinct frequency-lowering techniques that were designed to compensate in part for the perceptual effects of high-frequency hearing impairments. The Widex “Audibility Extender” is a linear frequency transposition scheme, whereas the Phonak “SoundRecover” scheme employs nonlinear frequency compression. Although these schemes process sound signals in very different ways, studies investigating their use by both adults and children with hearing impairment have reported significant perceptual benefits. However, the modifications that these innovative schemes apply to sound signals have not previously been described or compared in detail.MethodsThe main aim of the present study was to analyze these schemes'technical performance by measuring outputs from each type of hearing aid with the frequency-lowering functions enabled and disabled. The input signals included sinusoids, flute sounds, and speech material. Spectral analyses were carried out on the output signals produced by the hearing aids in each condition.ConclusionsThe results of the analyses confirmed that each scheme was effective at lowering certain high-frequency acoustic signals, although both techniques also distorted some signals. Most importantly, the application of either frequency-lowering scheme would be expected to improve the audibility of many sounds having salient high-frequency components. Nevertheless, considerably different perceptual effects would be expected from these schemes, even when each hearing aid is fitted in accordance with the same audiometric configuration of hearing impairment. In general, these findings reinforce the need for appropriate selection and fitting of sound-processing schemes in modern hearing aids to suit the characteristics and preferences of individual listeners.
Highlights
Two major hearing-aid (HA) manufacturers have recently introduced frequency-lowering sound processing schemes
The findings of the present study provide technical explanations for the perceptual benefits reported with use of both the linear frequency transposition (LFT) and nonlinear frequency compression (NLFC) frequency-lowering schemes
The input signals delivered to each HA comprised a sinusoid with slowly increasing frequency, a sequence of notes played on a flute, and four words chosen to contain many phonemes with dominant high-frequency components
Summary
Two major hearing-aid (HA) manufacturers have recently introduced frequency-lowering sound processing schemes. These schemes are technically dissimilar, they are both intended for HA users who have relatively poor hearing at high frequencies. Many people with sensorineural impairment have poorer hearing at high frequencies than at lower frequencies, as indicated by hearing sensitivity recorded on a pure-tone audiogram In such cases, other aspects of auditory perception in addition to sound sensitivity are often affected. The Widex ‘‘Audibility Extender’’ is a linear frequency transposition scheme, whereas the Phonak ‘‘SoundRecover’’ scheme employs nonlinear frequency compression These schemes process sound signals in very different ways, studies investigating their use by both adults and children with hearing impairment have reported significant perceptual benefits. The modifications that these innovative schemes apply to sound signals have not previously been described or compared in detail
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