Granulation enables independent control of pitch and duration

Pitch-time changing by granulation segments a sampled sound into grains, then independently manipulates playback rate and grain count to achieve separate control over pitch and duration. To double duration without changing pitch: clone each grain (two grains per original), keeping playback rate constant. To halve duration: delete every other grain. To shift pitch up by one octave without changing duration: double the playback sampling rate AND clone every grain (restoring the duration). To shift pitch down an octave: halve the playback rate AND delete every other grain. For arbitrary ratios, use proportional resampling with grain cloning and deletion. The grain envelope preserves local frequency content during the manipulation.

Examples

Time-stretch a vocal phrase by 3x: segment into 20ms grains, clone each grain 3 times. Pitch-shift up a fifth (1.498x) without changing duration: resample at 1.498x rate, then delete grains to restore original length.

Assessment

Describe the granulation algorithm for shifting a sound’s pitch up by one octave while keeping its duration unchanged. What operation on grains restores the duration after pitch-shifting?