[sdiy] USB to CV

[Richard Wentk]

At 23:02 13/04/2005, Neil Johnson wrote:
>Hi,
>
>On Wednesday, April 13, 2005, at 09:41  pm, Steve Begin wrote:
>>Has anybody ever seen / done this?  Is it even possible?
>>It seems like it might be useful if it there was a way to implement it.
>
>I guess you could do it with a USB Analogue I/O adaptor and a scaling amp 
>(to get 1V/oct).  Or were you thinking of a custom solution?

All USB audio adaptors have DC blocking caps. If you remove those - it's 
usually just a case of shorting across them with a solder link - and add a 
scalling and offset amp you have exactly what you need to do USB-> CV 
without bothering with MIDI.

The problem is then working out how to create CV-type audio. or use with a 
sequencer, create a string of samples at fs db and scale them with a mixer 
envelope. This will give you a controllable positive CV.

The best way to get a bipolar CV would be to subtract half the range in the 
offset stage. You now have a system where you can draw CV curves on the 
screen using the sequencers envelope tools. You lose one bit of resolution, 
but that hardly matters with 16-bit converters.

Of course if you want to play tunes from the sequencer instead of designing 
arbitrary CV curves, it's easier to stick with a USB MIDI to MIDI to CV.

Richard