Continuous tone sensation begins around 20-30 Hz pulse rate

The boundary between hearing a fluttering succession of distinct pulses and perceiving a continuous tone lies somewhere between 8 Hz and 30 Hz, with most estimates converging around 20-30 Hz. Below this rate, listeners hear individual impulses as rhythm. Above it, the impulses fuse into a continuous pitch via forward masking and perceptual integration. This threshold is the pivot point of the rhythm-pitch continuum: increasing pulse rate gradually shifts the percept from rhythm to drone to pitch. The exact boundary depends on the waveform, amplitude envelope, and listener.

Examples

A pulse train at 4 Hz sounds like a slow rhythm. At 15 Hz it sounds like a fast flutter. At 25 Hz it begins to have a pitch quality. At 50 Hz it is a clear pitch.

Assessment

At what pulse rate does a series of sound impulses begin to be perceived as a continuous tone? What is this called in the context of granular synthesis, and why does it matter for designing grain density parameters?