The gammachirp auditory filter and its application to speech perception

We review the gammachirp (GC) auditory filter and its use in speech perception research. The GC was originally developed to explain the asymmetric, auditory filter shapes derived in notched-noise (NN) masking studies, and the strongly compressive input-output function observed in the mammalian cochlea. This compressive GC was fitted to a very large collection of notched-noise (NN) masking thresholds measured with a wide range of stimulus levels and center frequencies. The fit showed how the GC auditory filter could explain NN masking throughout the domain of human hearing with a relatively small number of parameters, only one of which was level dependent. Subsequently, a dynamic, compressive GC filterbank (dcGC-FB) was developed to simulate time-domain cochlear processing. This dcGC-FB has been used to cancel the peripheral compression of normal hearing and thereby simulate the most common forms of hearing loss. This simulator allows normal hearing listeners to experience the difficulties of hearing impaired listeners. It has been used in training courses for speech-language-hearing therapists and psychoacoustic experiments. The dcGC-FB has also been used for modeling speaker size perception and predicting speech intelligibility with GEDI (the gammachirp envelope distortion index).