ITDs are frequency-independent physically yet frequency-dependent perceptually.

Evidence

Because the speed of sound does not vary with frequency, the time for a sound to travel from one ear to another does not depend on frequency. Consequently, both high-frequency and low-frequency sounds will produce an ITD of a fixed amount. However, the availability of this information to the ear does depend on frequency. A fixed delay corresponds to a different number of cycles for a low-frequency sound than for a highfrequency sound. — Jennifer Lentz, Psychoacoustics- Perception of Normal…, 1462

Categorization

• DEFINE: Frames the key distinction between physical ITD and its perceptual availability by frequency, prefiguring the phase-ambiguity problem for high frequencies.