[sdiy] AD/DA schematics? quantizers,etc

[Scott Nordlund]

Actually, now that I think about it a little more, I've tried a patch bay on a breadboard (while modifying a Siel MDP-40 drum machine), and didn't find it much more exciting than just using a switch to enable/disable each bit.  8 switches provides more than enough flavors of "nasty", at least as far as drum machines go, but it could be considerably more interesting for straight oscillator outputs (pre VCF/VCA) or CV purposes- I imagine a simple LFO waveform turning to some sort of strange pseudo-sequence.  Anyway it's trivial to play with it on a breadboard to see whether or not it's worth doing.  An (absurd?) extension of this would be to have adjustable weighting for each bit, though the DAC purchase would then become redundant as you'd be building your own (plus the linearity would depend on the adjustments...).

I would also recommend doing the pull-up/down resistor (or AND/OR/whatever logic if you want to try the LED bargraph voltage control method) the opposite way on the MSB so that the maximum offset produced by disabling bits is equal to the MSB rather than the full-scale voltage.  I guess there could be a more elegant way to do this, but it's better than nothing.

You could also use switches or X-OR gates to invert each bit individually, but this sort of thing runs into diminshing returns at some point...

You might want to use a separate sample and hold circuit to do the sample rate reduction, since these can be clocked at any frequency (down to 1 Hz if you feel like it) without risk of malfunction or damage to the ADC or DAC.  These could also be made into separate modules, though I don't know if this strays too far from the original intent...

----------------------------------------
> From: jerryge at cableone.net
> To: synth-diy at dropmix.xs4all.nl
> Subject: RE: [sdiy] AD/DA schematics? quantizers,etc
> Date: Wed, 13 May 2009 12:37:47 -0500
>
>
> The patch bay idea is cool!, you can do bit convolutions with that, it could
> yield some very dirty and interesting effects on audio signals. Just keep
> the pull down resistors on the D to A the switch version would use.
>
> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl
> [mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Andre Majorel
> Sent: Wednesday, May 13, 2009 12:24 PM
> To: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] AD/DA schematics? quantizers,etc
>
>
> On 2009-05-13 11:58 -0400, Scott Nordlund wrote:
>
>> Anyway, a properly-designed variant of that wouldn't be a bad
>> idea, you could even add a "patch bay" between the inputs and
>> outputs and map the inputs to the outputs any way you want,
>> resulting in some sort of primitive waveshaper that could
>> probably do some sort of frequency multiplication or something.
>> For audio purposes it's probably way too nasty but it might be
>> interesting for CV signals.
>
> http://www.teaser.fr/~amajorel/aubitswap/
>
> --
> André Majorel 
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