The grain envelope shape determines the spectral spread and character of a grain

Beyond duration, the shape of a grain amplitude envelope strongly colors the grain spectrum and its perceived character. The classical Gaussian envelope is the smoothest and gives the cleanest, most compact spectrum (highest sidelobe about -42 dB down). A quasi-Gaussian (Tukey/cosine-taper) keeps smooth attack and decay but adds a longer sustain, raising perceived amplitude while broadening the spectrum (highest sidelobe about -18 dB). A band-limited sinc envelope imposes a strong modulation, giving bubbling or frying textures. Asymmetric envelopes carry perceptual meaning: an expodec (sharp attack, exponential decay) articulates percussive rhythm and is useful as a convolution impulse response, while its reverse, the rexpodec, makes granulated sounds seem played backward even when they are not. Envelope choice is therefore a primary sound-design control, independent of grain duration or waveform.

Examples

Pure Gaussian 30ms grain: clean pitched tone. Quasi-Gaussian of the same duration: louder but buzzier (broader spectrum). Expodec grains: percussive, rhythm-articulating cloud. Rexpodec grains: same material sounds reversed.

Assessment

You have a granular cloud that sounds too clean and needs more percussive articulation. Which grain envelope would you switch to, and what perceptual cue distinguishes an expodec grain from its rexpodec reverse?