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

Oren Leavitt obl64 at ix.netcom.com
Thu Jul 8 04:41:12 CEST 2021


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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