Evaluation of critical bandwidth using digitally processed speech

Existing literature suggests that the hearing mechanism deals with incoming speech material by filtering the signals into a series of frequency bands. The width of these bands has been referred to as the critical band, that is, the perceptual frequency bandwidth observed in a variety of psychoacoustic contexts. Digital processing techniques have been developed for altering available recorded speech materials so that the frequency resolution available in the resultant stimuli may be controlled. Tapes have been produced wherein the frequency bandwidth resolution is limited to no better than one critical band and these tapes have been used in intelligibility testing. Some existing research indicates that the critical band is significantly widened in many individuals with sensorineural hearing loss of cochlear etiology. The digital processing routines described above were also used in developing tape recorded materials with bandwidth resolution limits considerably wider than the normal critical band. The bandwidths chosen for this stage of the digital processing were based on empirical observations of the critical band of sensorineural hearing impaired patients.