[sdiy] CEM3310/CEM3312 envelope level control (was Re: MIDI Velocity on analog synths)

[Tom Wiltshire]

Thanks for pointing that out, Michael. I'd never have spotted it otherwise.

The relevant ECO is ECO405, for anyone else who wants to have a look.

Both chips provide a connection to the comparator that switches from the Attack to the Decay stage. By feeding a voltage in there, Oberheim have changed the level at which the unit switches. This is virtually identical to what the CEM3312 does, although the 3312 breaks out the top of the voltage divider that feeds the comparator too, so you can stick the voltage in a slightly different place.

In both cases, it's not the same effect as a true VCA following the envelope, since you need to scale the Sustain level in conjunction with any changes to the Peak CV. But it makes the hardware simpler at the expense of another multiply in the software, and that was the name of the game I guess.

Tom


On 7 Feb 2014, at 02:56, Michael E Caloroso <mec.forumreader at gmail.com> wrote:

> Actually the CEM3310 does have a CV input that varies amplitude of the
> envelope.  Oberheim figured out how to do it in the OB8, it's in one
> of their ECOs.
> 
> MC
> 
>> What the CEM3310 doesn't have that the CEM3312 added is the Level CV to
>> avoid a separate VCA for amount control.