A granular texture sounds the same played backwards because the grain is time-invariant

Truax draws an analogy to quantum physics: at the grain level, time is reversible. Reversing an individual grain — even one derived from natural sound — leaves it perceptually unchanged, and consequently a whole granular texture played backwards sounds the same as played forwards. This time-invariance is a direct result of the grain’s brevity and of the statistical, non-narrative way grains are layered: there is no long-term temporal envelope or gesture to reverse. The property is surprising because ordinary recorded sound is highly direction-dependent (attacks become reversed swells). It is also the basis for pitch-preserving time manipulation: because a grain’s content is direction- and rate-independent, playback through a sample can be slowed or sped without altering pitch.

Examples

Reverse the audio of a dense granular cloud built from a cymbal sample: it sounds essentially identical forwards and backwards, whereas reversing the raw cymbal recording turns its sharp attack into a swell.

Assessment

Explain why a granular texture is perceptually reversible while an ordinary recording is not. Connect grain time-invariance to the ability to time-stretch without changing pitch.