For years the major focus in speech acoustics has been on the frequency range below approximately 5 kHz. Human speech and the human voice generate acoustical energy up to 20 kHz. Evidence is accruing that high-frequency energy (energy above 5 kHz) in speech and voice contributes to percepts of quality, localization, and intelligibility. The proposed research is intended to be an initial step in the long-range goal of characterizing high-frequency energy in speech, with particular regard for its perceptual role, its potential for modification during speech production, and its generation mechanism. In this study, a database of high-fidelity recordings of talkers will be used for broad acoustical analysis and general characterization of high-frequency energy, as well as specific characterization of phoneme category, speech intensity level, and mode of production by their high-frequency energy content. Directionality of radiation of high-frequency energy from the mouth will also be examined. The recordings will be used for perceptual experiments wherein listeners will be asked to discriminate between speech and voice samples that differ only in high-frequency energy content. Listeners will also be subjected to intelligibility-in- noise tasks with samples that have been modified only in high-frequency content. The combination of these experiments will reveal (1) the ability of human listeners to detect high-frequency energy modification, and (2) the phonetic value of high-frequency energy in speech.
The relevance of this project to public health lies in its efforts to elucidate the effect on human communicative behavior when high-frequency energy in speech is lost or altered, which may be incurred by factors such as hearing loss, noisy environmental conditions, telephony, audio data compression (such as mp3 compression), electronic sound reinforcement, or sound recording and playback. Previous research has already shown that high-frequency energy affects speech intelligibility, word-learning in normal-hearing and hearing-impaired children, speech localization, and qualitative percepts of speech and voice (e.g. 'naturalness'). Thus, this project will provide particularly valuable insight regarding the need for representation of the high-frequency range in augmentative hearing devices, including hearing aids, cochlear implants, and auditory brainstem implants;the results of this project may also impact the evaluation and management of speech, voice, and language disorders, as well as the development of training techniques for the enhancement of speech and voice.
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