Processing the telephone speech signal for the hearing impaired.
Speech intelligibility scores from 16 subjects with sensorineural hearing loss were evaluated using a digitized version of the California Consonant Test that was presented via headphones through a 300 to 3000 Hz bandpass filter to simulate the telephone band. Each subject was tested with an unprocessed signal that was frequency-equalized to compensate for the individual's hearing loss, and a signal that was equalized and compressed by the use of a compressor compression technique. Subjects were tested at three sound pressure levels above a pure-tone average threshold for frequencies 1 and 2 kHz. Two digital signal processing techniques designed to compensate for high-frequency hearing loss were examined: frequency domain processing and time domain processing. Frequency domain involved modification of the short-term spectrum obtained through a fast Fourier transform, whereas time domain processing involved passing the signal through a bank of finite impulse response filters. Both techniques showed significant intelligibility improvements (15-30%). In a second experiment, 16 additional subjects with high-frequency hearing loss compared an amplified telephone signal to three processed signals: (1) 6 dB per octave emphasis; (2) a signal frequency equalized for their hearing loss; and (3) a signal that was equalized for their hearing loss and was compressed according to their uncomfortable loudness levels. Most subjects preferred the signal with the 6 dB per octave emphasis.
Terry
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M
Department of Communication Disorders and Speech Science, University of Colorado, Boulder.
Bright
K
K
Durian
M
M
Kepler
L
L
Sweetman
R
R
Grim
M
M
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004560:Electricity; D005260:Female; D006310:Hearing Aids; D006311:Hearing Disorders; D006801:Humans; D008297:Male; D008875:Middle Aged; D012815:Signal Processing, Computer-Assisted; D013061:Speech Acoustics; D013065:Speech Intelligibility; D013689:Telephone / Q000295:instrumentation*; D013997:Time Factors