[sdiy] ODP: Re: Quantizer project.. incoming CV's switching point to change to quantized output CV's ...

Roman modular at go2.pl
Tue Jul 13 07:06:31 CEST 2021

My personal experience is that I'd rather spend $5 more on good linearity high resolution DAC than hassle with calibration of each note. Even if the calibration process is automated. 


---- Użytkownik Oren Leavitt via Synth-diy napisał ----

>I like that idea of a fine tuning DAC, too.
>Something I've experimented with in a MIDI to CV is to have one 
>dedicated DAC for octaves, and another 12 or 16 bit DAC for just the 
>note offset in between. The note value would be fetched from a lookup 
>table for whatever tuning was selected. The octave was simply the MIDI 
>note number modulo the length of the selected tuning table. The note 
>offset was the remainder.
>The analog outputs from the two DACs are summed together for the final CV.
>It worked out surprisingly well!
>I would imagine this would work equally well for the quantizer project 
>as well.
>On 7/7/21 8:38 PM, Brian Willoughby wrote:
>> This is an excellent suggestion, and should work for anything except very open tuned chords.
>> Even with wide chords, if each VCO gets its own Coarse and Fine then it will still work just fine.
>> One thing I was going to suggest is that the Coarse "DAC" could just be a set of switched resistors (or voltage references) that can produce exact 1 V steps. With 1V/octave, the Coarse could just select the octave range (and the Fine would not necessarily be limited to one octave).
>> Brian
>> On Jul 7, 2021, at 11:50, Jay Schwichtenberg via Synth-diy <synth-diy at synth-diy.org> wrote:
>>> Very simple solution for this.
>>> Just like for a regular VCO have a course and fine tune DAC, maybe 12-14 bits for the course and 8-10 bits for the fine. Just make sure they are decent DACs, especially that they are linear.
>>> Timing as far as writing both values shouldn't be a problem. One solution if you think it might would be use a dual DAC for both that has a sync function (output values and then send command to load the DACs simultaneously).
>>> Jay S.
>>> On 7/6/2021 10:19 PM, Brian Willoughby wrote:
>>>> In order to hit 701.995 cents, I assume you'll need a resolution of 0.005 cents on your DAC. If I'm doing the math correctly, that requires an 18-bit DAC, and I don't know any with DC output. That's just for 1 octave of range. If you want 5 octaves of range, you'll need a 20-bit DAC.
>>>> Are you talking about a practical design, Mike?
>>>> I know that 20-bit ADC and DAC were a thing before 24-bit delta-sigma, but I never went looking before. The first 18-bit DAC I found only guarantees 12-bit accuracy, but at least it's monotonic. I suppose one could spend more than $10 to get better accuracy.
>>>> Brian
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