[sdiy] Modulated ADSR Generator

[Matthew Smith]

Quoth Tim Parkhurst at 09/07/11 16:07...
...
> I'd probably include an input to scale the output level. Could be
> useful when driven with a velocity CV. The only thing is that you
> might not have the bit resolution to avoid stepping at very low output
> levels.

OK. From the response so far (thanks Dave, Paul, Tim,) I'd say that the 
analogue inputs should be:

6 x pots
2 x CV

Device is clocked at 12MHz, so I just need to be mindful of how fast I 
can sample my inputs. Pots obviously not an issue - people can't twiddle 
that fast ;-)

Anyone suggest a reasonable minimum CV sample rate? (I'll be running at 
4x minimum as there will be 4-sample averaging done to remove glitches.)

> What are the parameters you have in there now? I can see an overall
> Time CV as being very useful. Some other ideas might be Segment Shape
> (Lin, Log, Rev Log), Delay, or a second Release Time (like a sustain
> pedal effect).

I'm going to try to be as flexible as possible so that there will be so 
that there will be 8 or more parameters, of which you can assign 6 to 
the pots. Ditto on the two CVs - provide a choice of what they end up doing.

We had a discussion on the merits of various paramters back in February. 
(I'd forgotten that Andre Majorel suggested CV input back then.)

Parameters for the knobs would be:

* Attack time
* Attack shape
* Decay time
* Decay shape
* Hold level
* Sustain level
* Release time
* Release shape

...of which you get to assign six. I *could* do an analogue multiplex on 
more pots, but I'm trying to keep this simple both in terms of hardware 
and software.

So, I could either have extra parameters to which the CVs could be 
assigned, modulate the knob settings (5V CV in gives 100% the value set 
on a specified knob) or assign CVs directly to knob parameters.

If it transpires that I only need a minimal CV sampling rate, I may be 
able to just have 8 CV channels, which can be switched (with a physical 
SPDT switch) between external input and a set of 8 pots. The more 
flexible it can be, the better.

Looks like I'm going to need an LCD and a rotary encoder/switch for all 
those assignments ;-)

Note to self: Zener-clamp inputs to prevent Fried Microcontroller Syndrome.

Cheers

M

-- 
Matthew Smith

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