[sdiy] VCA signal analysis

cheater00 . cheater00 at gmail.com
Mon Dec 9 12:37:57 CET 2013

On Mon, Dec 9, 2013 at 12:15 PM, Rutger Vlek <rutgervlek at gmail.com> wrote:
> Hi all,
> About two years ago I came up with moderately new discrete OTA vca design in Spice and now I finally have it prototyped and it works (yay! hope it is of sufficient quality to overcome dependency on the more and more obsolete OTA ICs), but I'd like to do some more analysis on the circuit beyond stating that "it puts signal through in a VCA-ish manner and doesn't sound too bad". I'd like to measure distortion, noise, CV bleed, etc. What is currently the easiest way to measure such aspects? I've read about hardware analyzers (Audio Precision and the likes), but was hoping for something a bit more gentle on the wallet. Can something like that be done with PCs nowadays? And do I need a special I/O card for that? Or would a high-quality DC-capable sound card (like my MOTU 828 MK3) work for that too?
> Best,
> Rutger

A MOTU is OK as far as hardware, but you really want to take a look at
the software as well. The software is just as easy to make incorrect
or use wrong as the hardware. The APx software really shines in that
regard. You check boxes selecting what tests you want and you get a
nice report. If I were you I'd find someone with an APx and ask him
nicely to test the thing for you. Maybe pay them. It's maybe 15
minutes of work plus 10 minutes of waiting. Or maybe you could rent
out a box, I understand those are available at some places. Paying
someone to test the unit for you is probably going to be cheaper,


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