A. Boothroyd et al., THE HEARING-AID INPUT - A PHONEMIC APPROACH TO ASSESSING THE SPECTRALDISTRIBUTION OF SPEECH, Ear and hearing, 15(6), 1994, pp. 432-442
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.