Comparison of a short-time speech-based intelligibility metric to the speech transmission index and intelligibility data.

Several algorithms have been shown to generate a metric corresponding to the Speech Transmission Index (STI) using speech as a probe stimulus [e.g., Goldsworthy and Greenberg, J. Acoust. Soc. Am. 116, 3679-3689 (2004)]. The time-domain approaches work well on long speech segments and have the added potential to be used for short-time analysis. This study investigates the performance of the Envelope Regression (ER) time-domain STI method as a function of window length, in acoustically degraded environments with multiple talkers and speaking styles. The ER method is compared with a short-time Theoretical STI, derived from octave-band signal-to-noise ratios and reverberation times. For windows as short as 0.3 s, the ER method tracks short-time Theoretical STI changes in stationary speech-shaped noise, fluctuating restaurant babble and stationary noise plus reverberation. The metric is also compared to intelligibility scores on conversational speech and speech articulated clearly but at normal speaking rates (Clear/Norm) in stationary noise. Correlation between the metric and intelligibility scores is high and, consistent with the subject scores, the metrics are higher for Clear/Norm speech than for conversational speech and higher for the first word in a sentence than for the last word.

Effect of slow-acting wide dynamic range compression on measures of intelligibility and ratings of speech quality in simulated-loss listeners.

The purpose of this study was twofold: (a) to determine the extent to which 4-channel, slow-acting wide dynamic range amplitude compression (WDRC) can counteract the perceptual effects of reduced auditory dynamic range and (b) to examine the relation between objective measures of speech intelligibility and categorical ratings of speech quality for sentences processed with slow-acting WDRC. Multiband expansion was used to simulate the effects of elevated thresholds and loudness recruitment in normal hearing listeners. While some previous studies have shown that WDRC can improve both speech intelligibility and quality, others have found no benefit. The current experiment shows that moderate amounts of compression can provide a small but significant improvement in speech intelligibility, relative to linear amplification, for simulated-loss listeners with small dynamic ranges (i.e., flat, moderate hearing loss). This benefit was found for speech at conversational levels, both in quiet and in a background of babble. Simulated-loss listeners with large dynamic ranges (i.e., sloping, mild-to-moderate hearing loss) did not show any improvement. Comparison of speech intelligibility scores and subjective ratings of intelligibility showed that listeners with simulated hearing loss could accurately judge the overall intelligibility of speech. However, in all listeners, ratings of pleasantness decreased as the compression ratio increased. These findings suggest that subjective measures of speech quality should be used in conjunction with either objective or subjective measures of speech intelligibility to ensure that participant-selected hearing aid parameters optimize both comfort and intelligibility.