Oscillations, Waves, and Interactions - GWDG

42 A. Kohlrausch and S. van de Par
Figure 3. Responses of a linear
basilar-membrane model at resonance
frequency 1100 Hz to the three harmonic
maskers with fundamental frequency
100 Hz shown in Fig. 1. The top
panel shows the zero-phase signal, the
middle panel the negative Schroeder
phase and the bottom panel the positive
Schroeder phase complex. Reused
with permission from Ref. [9]. Copyright
1995, Acoustical Society of America.
The most important conclusion was that, for the right choice of input parameters,
the phase characteristic of a Schroeder-phase stimulus matches quite closely this
phase characteristic of the auditory filter, at least in the spectral region of maximum
transfer of the filter. Since Schroeder-phase stimuli come in two flavours, one version,
the negative Schroeder-phase stimulus, will have the same phase characteristic as the
auditory filter while the positive Schroeder-phase stimulus has a phase spectrum
that is opposite to that of the filter. In the transfer through a filter, the input
phase spectrum and the filter phase spectrum add to give the phase spectrum of the
output signal. For the positive Schroeder phase, we thus have the situation of phase
compensation, and the resulting filtered signal at the output of the auditory filter
has a nearly constant phase of all components. Conceptually, this situation is quite
similar to pulse compression through frequency modulation, as it is used in radar
and sonar technology. In a way, the positive Schroeder-phase stimuli are matched in
their phase characteristic to the auditory filters as they are realized mechanically in
the inner ear.
This interpretation has some interesting consequences: if a specific Schroederphase
stimulus is optimally matched in its phase to the inner ear filter at a certain