[sdiy] CV from soundcard

[Paul Schreiber]

>
> Most soundcards have *much* better converters than a typical MIDI/CV  box, 
> so aside from that minor scaling tweak you should get better CV 
> performance overall.


Ummmmmm.....not hardly. #bits does NOT equal *accuracy*. Most audio DACs are 
quite crappy for DC accuracy (that's why they are designed to be *audio* 
DACs). The ear is quite forgiving having adjacent samples "off" DC-wise at a 
high (say 48Khz) sample rate. You are more likely to hear transient 
*artifacts* from audio DACs (such as clock jitter) than absolute 
sample-to-sample, DC accuracy. Besides, if sample N is "off" but is N+1 is 
"correct"  21us later, you are not going to leap up out of your chair 
because it "didn't sound right".

It's a different story altogether when forcing a 'static' value (albeit one 
updated at the sample rate), in fact I will bet that voltage will "wander" 
sample-to-sample but probably below making a VCO shift enough to hear (it's 
integrated anyway).

Many sigma-delta DACs are sort of like DRAMS: they are designed to be a 
*clocked* system: they themselves are not 'static' in the sense a 
traditional DAC is. Also, what about the DC accuracy/drift of the components 
"downstream" of the DAC itself? Are you going to convince me a JRC4556 or 
4580 headphone op amp that cost 11 cents is "good enough" as a CV source?

Paul S.
/former DAC designer, Crystal Semi and Maxim Semi