Pitch-synchronous granular synthesis aligns grain envelopes with the waveform period to reduce audio artifacts

In pitch-synchronous granular synthesis, overlapping grain envelopes are designed to be synchronous with the frequency of the grain waveform, so successive grains overlap in phase with the fundamental. This avoids the amplitude cancellations and spectral artefacts that arise when arbitrary grain boundaries cut across the waveform at random phase. It is used when a clean, pitched output is needed — speech synthesis, formant manipulation, sustained melodic tones. The cost is that the pitch must be known or estimated to set the synchronisation period, making pitch-synchronous synthesis less suitable for unpitched or noisy sources than asynchronous methods.

Examples

Synthesising a sustained 220 Hz vowel: grain length set to one period (about 4.54 ms), each grain starting where the previous period ends, gives a clean harmonic spectrum. Random boundary placement would instead produce phase-cancellation sidebands.

Assessment

Explain why phase-aligning grain boundaries reduces artefacts in pitched granular synthesis. Give a source type where pitch-synchronous synthesis is impractical. Compare the spectral output of pitch-synchronous vs asynchronous synthesis on the same pitched source.