[sdiy] Digital pots for polyphonic portamento..

[Jean-Pierre Desrochers]

> Are you planning to use a MAX551 for each voice?

Yes.
Velocity, Pitch bend, Mod wheel, After touch, CC0, CC1
will have 8bits DAC's each.
I have a bunch of DAC0800 on hand for it so...
Software method.. Good idea! But I don't want to load
the 'analysis' time for each received MIDI bytes to CV outs.. wondering..
I'm using a PIC16F877 at 20mHz.
JP

----- Original Message ----- 
From: "Simon Brouwer" <simon.oo.o at xs4all.nl>
To: <Synth-diy at dropmix.xs4all.nl>
Sent: Wednesday, March 04, 2009 4:38 PM
Subject: Re: [sdiy] Digital pots for polyphonic portamento..


> Colin f schreef:
>>
>>> I'm building my MIDI2CV mono/poly module and have one question..
>>> I'm gonna have 6 voices CV's outs on my polyphonic mode
>>> and want to use a portamento pot that would control all 6 voices
>>> at the same time. I was guessing to use 3 dual 1meg digital pots (6 pots 
>>> overall)
>>> (Analog Device AD5242) and 6 caps to make the porta voltage glidings..
>>> Those are 256 taps which makes 1meg/256 = 3906ohms per steps (+ 60 ohm 
>>> for wiper).
>>> These would be place right between my MAX551 DAC's 0-5v outs and my 
>>> precision opamp voltage followers. I don't want to create CV's 1v/oct 
>>> unprecision using them so..
>>>
>>
>> If you're using a 12-bit convertor, do the portamento in software.
>> With any half decent modern microcontroller, you'll easily be able to
>> produce 6 simulated RC curves that you wont be able to tell apart from 
>> the
>> real RC circuits.
>> And software can easily provide alternate portamento modes, such as 
>> linear,
>> fixed time linear, glissando, etc.
>>
> I agree. With a glide circuit on each voice notes would glide, more or 
> less haphazardly, from whatever note happened to be previously assigned to 
> that voice.
> Gliding from the previously played note probably gives a more pleasing 
> effect. But that note is likely to have been assigned to another voice. 
> Implementing this in software is probably the easiest, and does not affect 
> the CV precision.
>
> Are you planning to use a MAX551 for each voice?
>
> -- 
> Vriendelijke groet, Simon Brouwer.
> | http://nl.openoffice.org | http://www.opentaal.org |
>
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