[sdiy] Modulated ADSR Generator

[Matthew Smith]

Quoth Dave Manley at 10/07/11 02:44...
> This is what I intended for the CV input - scale all times together.
> One obvious use: keyboard CV affects overall envelope time, which
> mimic many instruments - high notes decay faster.  You don't have to
> sample the CV often, only at the trigger event, or only at each segment
> start.

Aha! That's good news. The lower the sample rate, the better. Not that 
I'm really worried about jitter in an application like this, even when 
in LFO mode, but the less that's going on at any given time, the better.

> What will you do if the gate ends during the attack phase?  Immediately
> go to release, or let the full time for each segment complete?  There
> are advantages to both approaches, so there's another option.

Both :-) I take the points regarding having too many options, but want 
to provide maximum flexibility. So would probably have some basic 
options, then 'advanced' settings.

> Will you support inverted envelopes?

If it would be useful.

At this stage, the important thing is to make sure all the hardware that 
might be needed will be there.  Think I'll be going for two pots and two 
CVs - possibly with switchable pull-up resistors on the CV inputs so 
that they can also be used as footswitch inputs. (I'd do this by routing 
the analogue inputs back to spare IO pins, via a 10k resistor. In 
"normal" mode, the IO pins would be configured as inputs (high Z,) then 
switchable to outputs at logic 1 for when a switch is required.)

Trigger and gate signals to be opto-isolated with socketed DIP isolators 
for easy replacement when they get fried. (Will probably be the only 
non-SMD components, barring connectors.)

Get the hardware right, and the rest is all a matter of firmware. And 
yes, Dan, C source, Eagle CAD files will be published. If there is 
interest, I'll also source bare boards and fully assembled/tested units. 
(I'm including an ISP connector so they can be easily re-flashed with 
new/different firmware.) Not going for a "standard" modular form-factor 
at this point as I'm just trying to get it as small as possible to keep 
costs down and to fit all modules behind as small a (single) front panel 
as I can manage.

As my PCB guy does everything in threes, I might figure out a way of 
ganging three together so they can operate of a common trigger/gate 
pair. With the DCO I'm working on producing three simultaneous outputs 
(fundamental, -1 8ve, -2 8ve,) I'd like to be able to have them with 
their own envelopes.

Cheers

M

-- 
Matthew Smith

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