THE HEARING-AID INPUT - A PHONEMIC APPROACH TO ASSESSING THE SPECTRALDISTRIBUTION OF SPEECH

Objectives: The long-term goal is to investigate the feasibility of us ing real speech as a stimulus for electroacoustic evaluation of nonlin ear hearing aids. The goals of the present study were to determine the spectral envelope of speech from acoustic measures of phoneme tokens in running speech, to compare the results with published data on long- term average speech spectra, to measure intertalker differences of spe ctral envelope, and to explore the extent to which the intensity varia tion within and across talkers might be minimized by frequency-selecti ve amplification and automatic gain control. Design: Seven phonemes we re selected to represent the extremes of frequency and intensity in En glish. Recordings were made of five men and five women producing sylla ble strings constructed from these phonemes. One-third octave spectra were prepared from the phoneme tokens. The frequencies and intensities of 13 key points in these spectra were measured and used to estimate individual and group spectral envelopes. Results: The group spectral e nvelope was similar to that derived from published data on the long-te rm average spectrum of speech, but there were marked intertalker diffe rences. Some of the differences were gender-related. The overall dynam ic range of intensity in these data was 53 dB. Frequency-dependent lev el adjustment (an 11 dB high-frequency boost) reduced this range to 42 dB, and a combination of frequency-dependent and subject-dependent le vel adjustment (analogous to 2-band automatic gain control) reduced it to 37 dB. Conclusion: A phonemic approach to determining the spectral envelope of speech offers insights that are not available from long-t erm average spectra and could offer advantages in the evaluation of no nlinear hearing aids.