irise -- rise time in seconds. A zero or negative value signifies no rise modification.
idur -- overall duration in seconds. A zero or negative value will cause initialization to be skipped.
idec -- decay time in seconds. Zero means no decay. An idec > idur will cause a truncated decay.
kamp, xamp -- input amplitude signal.
Rise modifications are applied for the first irise seconds, and decay from time idur - idec. If these periods are separated in time there will be a steady state during which amp will be unmodified. If linen rise and decay periods overlap then both modifications will be in effect for that time. If the overall duration idur is exceeded in performance, the final decay will continue on in the same direction, going negative.