[sdiy] ADSR Trigger/Retrigger behaviour

[Tom Wiltshire]

On 27 Jun 2014, at 14:08, Justin Owen <juzowen at gmail.com> wrote:
> Most diagrams show the Attack section starting from whatever output level the ADSR was at when the Trigger was received. Two examples are this one from MFOS (top right):
> 
> http://www.musicfromouterspace.com/analogsynth_new/ADSR001/ADSR001_cyclediags.gif
> 
> and the diagram in the Doepfer A-140 manual.
> 
> ...so is this standard? The ADSR rests to the Attack stage but the Attack starts at whatever level it was at when the Trigger was received - or (perhaps just in an ideal world...) would you expect the Attack stage to be reset fully and start from 0V?

Starting from 0V would make an abrupt drop in the output level and a nasty click in whatever you fed the envelope to. So it's much better to start from the existing level, whatever that is. Yes, I'd say it's as close to standard as the synth world gets, which is to say everyone seems to do it that way.

There's  a related question of whether the attack time should remain the same (e.g. do the whole attack time) or whether it should be proportional to it's starting point. The first way means that higher starting levels give a much shallower attack slope, although they keep the same time. The other way is to keep the slope constant, but adjust the time. This second way means notes played after notes with slow releases get shorter attacks.

The CEM3310 and SSM2056 env gen chips start from the current level like your diagrams. They also keep the slope constant, so starting further up gives shorter attack times.

HTH,
Tom