Figure 2.

Harmonic resolvability and cross-channel structure. A, Amplitude and phase spectrum of two gammatone filters. Only a pure tone of frequency f (“Input” waveform) is attenuated in the same way by the two filters (red and blue waveforms: filter outputs). At that frequency, the delay between the outputs of the two filters is δ = Δφ/f. B, If several harmonic components fall within the bandwidths of the two filters, then the outputs of the two filters differ (no cross-channel similarity). C, Excitation pattern produced on the cochlea by a harmonic complex. Top, Amplitude versus center frequency of gammatone filters. Bottom, Spectrum of harmonic complex and of gammatone filters. Harmonic components are resolved when they can be separated on the cochlear activation pattern. Higher-frequency components are unresolved because cochlear filters are broader. D, Resolved components produce cross-channel similarity between many pairs of filters (as in A). Unresolved components produce little cross-channel structure (as in B). E, Thus, the vibration pattern produced by resolved components displays both within-channel and cross-channel structure (left), while unresolved components only produce within-channel structure (right).