env

Apply an attack ramp and exponential decay envelope to a signal.

Signature

signal.env(attack_s, decay_s) -> Signal
// or equivalently:
env(signal, attack_s, decay_s) -> Signal

• attack_s — linear ramp from silence to full at the start of the buffer. 0.0 means “no ramp” (the buffer starts at full amplitude on sample 0).
• decay_s — exponential decay time constant. Larger values = longer ring. The envelope falls to 1/e (≈ 37%) after decay_s seconds and to ~5% after 3 × decay_s.

The envelope is applied multiplicatively per-sample; the source buffer’s length is unchanged.

Example

// A quick "click" that decays to inaudible in ~150 ms:
sine(2000.0, 0.2).env(0.001, 30.0)

// A long ringing tone — 4-second time constant means it's still
// at ~6% after 12 seconds. Combine with a finite buffer length.
sine(220.0, 8.0).env(0.01, 4.0).gain(0.4)

// No attack (hard onset, used for percussive transients):
noise("white", 0.05).env(0.0, 100.0).gain(0.5)

Why exponential

Exponential decay matches the way natural resonators (strings, bells, hulls) lose energy and is what listeners associate with “ringing”. Linear decay sounds artificial — it stays loud and then suddenly stops.

Future variants

A separate ADSR envelope (attack/decay/sustain/release) and a data-driven multi-segment envelope will land when patches that need them justify the API surface.