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 (15-3070). 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. (Ear Hear 13 2:70-79)
Speech intelligibility scores from hearing-impaired subjects were evaluated using a computerized version of the California consonant test. The speech signal was presented through a 300-to 3000-Hz bandpass filter (to simulate a telephone signal) via earphones. Each subject was tested with an unprocessed signal, with a signal that was amplified and equalized to compensate for the individual's hearing loss, and with a signal that was amplified, equalized, and compressed using compressor compression. Subjects were tested at three sound pressure levels above threshold. Two modes of digital processing were examined: processing in the frequency domain, that is, modification of the short-term spectrum obtained through an FFT; and processing in the time domain, that is, passing the signal through a bank of bandpass FIR digital filters whose gains had been adjusted to fit the hearing loss of the subject. Results for 12 subjects with sensorineural hearing loss show significant improvement in intelligibility scores (15%–30%) using both processing techniques. [Work supported by US West.]
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