The auditory system resolves frequency within critical bands: components within one band interact, components in separate bands do not

The critical band is the auditory system’s fundamental unit of frequency resolution, first identified by Harvey Fletcher (1940) through masking experiments. Within one critical band (~100 Hz wide at low frequencies, ~1/3 octave at high frequencies), tones interact perceptually: they mask each other, fuse in timbre perception, and contribute to perceived roughness. Tones in separate critical bands are perceived more independently. The critical band determines: (1) Masking: a loud tone masks softer tones within its critical band. (2) Timbre fusion: partials within a critical band contribute less distinguishable timbre than those spread across bands. (3) Roughness and dissonance: two tones within a critical band sound rough; those more than one band apart are consonant. There are approximately 24 critical bands (Bark scale) spanning the hearing range.

Examples

At 1 kHz, the critical band is approximately 160 Hz wide. A 1000 Hz and 1100 Hz tone played together create beating and roughness—they fall within one critical band. A 1000 Hz and 2000 Hz tone played together sound relatively smooth—in separate critical bands.

Assessment

Explain why a dense cluster of frequencies around 500 Hz masks more effectively than the same cluster spread across 500–2000 Hz. Use the concept of critical bands in your answer.