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. 2013 Mar;17(1):54-68.
doi: 10.1177/1084713813480856.

Nonlinear frequency compression: effects on sound quality ratings of speech and music

Vijay Parsa  1 , Susan Scollie, Danielle Glista, Andreas Seelisch
Affiliations

Nonlinear frequency compression: effects on sound quality ratings of speech and music

Vijay Parsa et al. Trends Amplif. 2013 Mar.

Abstract

Frequency lowering technologies offer an alternative amplification solution for severe to profound high frequency hearing losses. While frequency lowering technologies may improve audibility of high frequency sounds, the very nature of this processing can affect the perceived sound quality. This article reports the results from two studies that investigated the impact of a nonlinear frequency compression (NFC) algorithm on perceived sound quality. In the first study, the cutoff frequency and compression ratio parameters of the NFC algorithm were varied, and their effect on the speech quality was measured subjectively with 12 normal hearing adults, 12 normal hearing children, 13 hearing impaired adults, and 9 hearing impaired children. In the second study, 12 normal hearing and 8 hearing impaired adult listeners rated the quality of speech in quiet, speech in noise, and music after processing with a different set of NFC parameters. Results showed that the cutoff frequency parameter had more impact on sound quality ratings than the compression ratio, and that the hearing impaired adults were more tolerant to increased frequency compression than normal hearing adults. No statistically significant differences were found in the sound quality ratings of speech-in-noise and music stimuli processed through various NFC settings by hearing impaired listeners. These findings suggest that there may be an acceptable range of NFC settings for hearing impaired individuals where sound quality is not adversely affected. These results may assist an Audiologist in clinical NFC hearing aid fittings for achieving a balance between high frequency audibility and sound quality.

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Conflict of interest statement

Declaration of Conflicting Interests: The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Figures

Figure 1.
Figure 1.
Narrowband spectrograms of a speech stimulus “Would you please give us the facts? She arrived home early that night” spoken by a female talker that was processed through different frequency compression settings. Note. (a) No nonlinear frequency compression, (b) frequency compression with CF = 4000 Hz and CR = 2:1, (c) frequency compression with CF = 3000 Hz and CR = 2:1, and (d) frequency compression with CF = 2000 Hz and CR = 2:1.
Figure 2.
Figure 2.
Screenshot of the MUSHRA software used to gather the quality ratings of frequency-compressed speech stimuli.
Figure 3.
Figure 3.
Mean speech quality ratings for the four groups of listeners, averaged across the two male talkers. Note. NFC settings are denoted by the CR and CF parameters.
Figure 4.
Figure 4.
Mean speech quality ratings for the four groups of listeners, averaged across the two female talkers. Note. NFC settings are denoted by the CR and CF parameters.
Figure 5.
Figure 5.
Averaged NH and HI quality ratings for the speech in quiet condition. Note. NFC settings are denoted by the CF parameter.
Figure 6.
Figure 6.
Averaged NH and HI quality ratings for the speech in noise condition. Note. The frequency compression settings are denoted by the CF parameter.
Figure 7.
Figure 7.
Average rating of contemporary music. Note. The score appears on the left axis and processing condition on the bottom axis. Darker are lighter bars denoting NH and HI ratings, respectively. Whiskers on the top of the bar graph show one positive standard deviation.
Figure 8.
Figure 8.
Average rating of classical music. Note. The score appears on the left axis and processing condition on the bottom axis. Darker are lighter bars denoting NH and HI ratings, respectively. Whiskers on the top of the bar graph show one positive standard deviation.
See this image and copyright information in PMC

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