frac32 decay time
bool32.risingfalling trigger
frac32buffer.positive envelope output
frac32.u.map d
int32_t val;
val = 0;
if (inlet_trig > 0)
val = 1 << 27;
else
val -= ___SMMUL(val, (param_d + inlet_d) >> 1);
outlet_env = val;