The Relative Importance of Spectral and Temporal Resolution for Fricative Identification

Allison A. Witte

Committee:

Joshua Alexander, Ph.D. (Chair)

Keith Kluender, Ph.D.

Previous studies have indicated the importance of high frequency cues for fricative identification. It is unknown how much temporal and spectral detail must be maintained in the high frequency signal for accurate fricative identification. Understanding the cues necessary for transmission of high-frequency speech information can help inform signal processing strategies intended to preserve or enhance them in hearing aids and cochlear implants. Results from multiple studies suggest that gross spectral and temporal information is sufficient for conveying these high frequency cues. This study aims to determine how the number of independent bands and the amount of temporal detail influences fricative identification in normal-hearing listeners. We hypothesize that vocoding the temporal envelope over a finite number of bands will lead to equivalent speech identification as the intact wideband signal. Fricatives spoken by 3 female talkers in an /iC/ context were vocoded using 1-4 channels per Equivalent Rectangular Band (3-12 channels total) with envelop cutoff frequencies ranging from 8 to 128 Hz. Results will help provide an understanding about the appropriate settings and hearing losses for current frequency lowering techniques as well as suggest ways in which future techniques might be designed to most effectively transmit wideband information over a narrower band.