Effects of Adaptation Rate and Noise Suppression on the Intelligibility of Compressed-Envelope Based Speech

Abstract

Temporal envelope is the primary acoustic cue used in most cochlear implant (CI) speech processors to elicit speech perception for patients fitted with CI devices. Envelope compression narrows down envelope dynamic range and accordingly degrades speech understanding abilities of CI users, especially under challenging listening conditions (e.g., in noise). A new adaptive envelope compression (AEC) strategy was proposed recently, which in contrast to the traditional static envelope compression, is effective at enhancing the modulation depth of envelope waveform by making best use of its dynamic range and thus improving the intelligibility of envelope-based speech. The present study further explored the effect of adaptation rate in envelope compression on the intelligibility of compressed-envelope based speech. Moreover, since noise reduction is another essential unit in modern CI systems, the compatibility of AEC and noise reduction was also investigated. In this study, listening experiments were carried out by presenting vocoded sentences to normal hearing listeners for recognition. Experimental results demonstrated that the adaptation rate in envelope compression had a notable effect on the speech intelligibility performance of the AEC strategy. By specifying a suitable adaptation rate, speech intelligibility could be enhanced significantly in noise compared to when using static envelope compression. Moreover, results confirmed that the AEC strategy was suitable for combining with noise reduction to improve the intelligibility of envelope-based speech in noise.

A Study of Joint Effect on Denoising Techniques and Visual Cues to Improve Speech Intelligibility in Cochlear Implant Simulation

“…Using vocoder simulations for the NH listeners under various background noise, speech maskers or numbers of electrodes were found in many previous studies as the proven strategy to understand and further provide basic information on the speech processing in CI users [55], [56], [57], [58], [59], [25], [60]. However, vocoder simulations were not used for estimating the precise level of performance for each single CI user.…”

Improving the Intelligibility of Speech for Simulated Electric and Acoustic Stimulation Using Fully Convolutional Neural Networks

“…Amplitude Envelope and Spectrogram Analyses on Vocoded Speech In addition to waveform and spectrogram plots, amplitude envelope plots are another useful tool for analyzing time-varying signals [97,98]. Previous studies [85,97,98] have reported a positive correlation between the modulation depth of the amplitude envelope and speech intelligibility. It has also been shown that the middle frequency band is more important for speech intelligibility than the low-and high-frequency bands.…”

“…In addition, vocoder has a profound impact on CI research. Using vocoder, speech signals are processed to simulate the sound heard by CI users, and the simulations are presented to NH participants for listening tests for various purposes, such as predicting the general pattern of speech recognition performance of CI users [14,[63][64][65]. Research using vocoder simulations may solve patient-recruitment issues as well as avoid patient-specific confounding factors, such as neural surviving patterns [64,66].…”

Improved Environment-Aware–Based Noise Reduction System for Cochlear Implant Users Based on a Knowledge Transfer Approach: Development and Usability Study (Preprint)

“…The participants were instructed to repeat verbally what they had heard. We evaluated the speech intelligibility under each test condition using the word correct rate (WCR) [38][39][40][41][42] calculated as the ratio between the number of correctly identified words and the total number of words. To further prevent participant fatigue, tests were paused for 5 minutes every 30 minutes.…”