Enhancement of speech intelligibility for hearing‐impaired subjects for a telelphone bandwidth

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 (...