Contour

ATMOSYNTH built-in module

A shape a note makes for something else to follow, as a Moog’s contour makes it: it rises from nothing to one and falls back, each stage a capacitor charging or emptying rather than a straight line. It makes no sound. Patch it into a modulation input — a filter’s Cutoff above all — and how far it moves what it reaches is set there. Delay waits before it begins. Attack is the time from nothing to one: it charges fast off the mark and arrives still moving, which is the snap a hardware envelope has and a straight line lacks. Hold keeps it at one. Decay falls to the Sustain level, which it holds while the key is down, and Release falls to nothing once the key is let go, from wherever the shape had got to, mid-attack included. Decay and Release are the time a whole fall from one to nothing takes. What each sets is how fast the shape falls, as on an analog envelope, so a decay to a sustain of a half, or a release from below one, arrives sooner than its knob says. Loop, while the key is held, takes the decay back round to the delay and the attack rather than resting at the sustain, so a held note becomes a slow wave of the contour’s own shape, falling to the sustain level each time round. Let go, it releases from wherever it was. Velocity is how much the strength a key was struck with counts. At nothing it counts for nothing; at one a key struck at half strength takes the shape half as high. A bass that barks only when it is dug into is a filter this opens, with Velocity turned up. A note slid into under a glide is the same note moved, so the shape carries on where it was and keeps the strength it was struck with; a new note starts from nothing. This module carries code because an envelope the vocabulary can draw is laid down by the clock at the moment a key goes down: it cannot stop an attack where it reaches one from wherever it began, nor go round again for as long as a key nobody can see the end of is held.