[sdiy] Midi knob box

[David Brännvall]

I am not a sdiy:er yet, well I kind of am one if you count softsynths. Anyway I need a midi knobbox, and I thought it would be nice to build my own. I don't have the skills to do it on my own. I have a crazy idea that should work, it is ovious that this is a really BAD way of doing it. Let me explain why. First I route 4 mono channels out from my audio card, into 4 mono channels on my mixer. Then I let the computer generate sinwaves, ie 1 khz on channel 1, 2 khz on channel 2, 3 khz on 3, 4 khz..., then route the mixed signal back in to my computer (via one subgroup on the mixer). Then I have to write a simple program to detect the amplitude of the different frequencys (fouriertransform or something), and convert it to midicontroller messages. And voila the volume sliders on my mixer can be used to generate midi control data. Although this should be simple to implement and it wouldn't cost me a dime, it would waste alot of audio ios, midi ports, mixer channels, cpu power etc.!
  So what I really need is a real knobbox, would it be cheaper to build it, or buy it? Where can I find info/schemas.

Please help me to get started.

regards,
David