Granular synthesis changes a sound's duration independently of its pitch

Because a grain’s pitch is fixed by the waveform inside it, not by the rate at which grains are triggered or the rate at which the playback head advances through the source, the two are decoupled — the passage of time can be changed independently of pitch. To slow a sound, advance the playback position through the source more slowly (overlapping or repeating grains) while reading each grain’s internal content at its normal rate: duration lengthens but pitch stays constant. To shift pitch without changing tempo, hold the position advance at full rate and read grains faster or slower. This is fundamentally different from slowing tape, which changes pitch together with speed; a common misconception is that changing playback rate achieves time-stretching. The overlap parameter fills the temporal gaps between grains — too little overlap causes audible dropout — and at extreme stretch ratios the grain repeat/overlap becomes audible as a stuttering, smeared, or ‘frozen’ artefact. This is the theoretical basis for the pitch-preserving time-stretch in every modern DAW.

Examples

Advance very slowly through a spoken-voice file while emitting grains: speech is stretched and smeared with pitch intact. A 100 BPM bassline stretched to 80 BPM by overlapping grains more heavily — same pitch, slower tempo. DAW modes like Ableton’s Complex Pro apply the same grain-based idea.

Assessment

Explain why moving slowly through a source with a granular engine lengthens duration without dropping pitch, whereas slowing tape does not. To play a 120 BPM loop at 90 BPM with unchanged snare pitch, which granular parameters change and which stay constant? Name the artefact that appears if grain overlap is too low or the stretch ratio is extreme.