The effects of nonlinear signal processing on speech intelligibility in noise are difficult to evaluate. Often, the effects are examined by comparing speech intelligibility scores with and without processing measured at fixed signal to noise ratios (SNRs) or by comparing the adaptive measured speech reception thresholds corresponding to 50% intelligibility (SRT50) with and without processing. These outcome measures might not be optimal. Measuring at fixed SNRs can be affected by ceiling or floor effects, because the range of relevant SNRs is not know in advance. The SRT50 is less time consuming, has a fixed performance level (i.e., 50% correct), but the SRT50 could give a limited view, because we hypothesize that the effect of most nonlinear signal processing algorithms at the SRT50 cannot be generalized to other points of the psychometric function.
In this article, we tested the value of estimating the entire psychometric function. We studied the effect of wide dynamic range compression (WDRC) on speech intelligibility in stationary, and interrupted speech-shaped noise in normal-hearing subjects, using a fast method-based local linear fitting approach and by two adaptive procedures.
The measured performance differences for conditions with and without WDRC for the psychometric functions in stationary noise and interrupted speech-shaped noise show that the effects of WDRC on speech intelligibility are SNR dependent.
We conclude that favorable and unfavorable effects of WDRC on speech intelligibility can be missed if the results are presented in terms of SRT50 values only.
1Department of Clinical and Experimental Audiology, Academic Medical Center, Amsterdam, The Netherlands; 2Department of Otorhinolaryngology and Head & Neck Surgery, and 3Brain Center Rudolf Magnus, University Medical Center Utrecht, Utrecht, The Netherlands.
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The authors have no conflicts of interest to disclose.
Received October 9, 2014; accepted July 16, 2016.
Address for correspondence: Koenraad S. Rhebergen, PhD, Department of Otorhinolaryngology and Head & Neck Surgery, University Medical Center Utrecht, Room F02.5. 57, PO Box F02.504, Postbus 85500, 3508 GA Utrecht, The Netherlands. E-mail: firstname.lastname@example.org