FW: [sdiy] DIY Mixer - please help!

[Jerry Gray-Eskue]

I was not quite clear on the whole signal path I described below here what I
meant:

Signal in > Boost [Your VCA goes here] > Signal at +- 10volts Max > Mix
[divide by number of active channels] > Buss - Signal at +- 10volts Max >
Out [ Level Out Control goes here]



-----Original Message-----
From: Jerry Gray-Eskue [mailto:jerryge at cableone.net]
Sent: Thursday, September 03, 2009 7:45 AM
To: cheater cheater
Subject: RE: [sdiy] DIY Mixer - please help!




-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of cheater cheater
Sent: Wednesday, September 02, 2009 3:48 PM
To: synth-diy
Subject: [sdiy] DIY Mixer - please help!

<< ...
Each channel is one VCA that has CV inputs, a single input, and a
single output to a single bus. Of course a stereo channel is that
multiplied by 2. With a CV approach it's going to be very easy to
control two channels with just the fader of the left channel, but
that's a trivial comment.
The bus sums and gives a single high-headroom output.
...>>

I am no expert on consoles but have a few thoughts.

If you want high quality sound this equates to Low Noise and Low Distortion.

What high head room gives you is signal levels much larger than the noise
floor and room to add signals of high level while running in the non
distorting region (not bumping into the distortion near the rails).

You should be able to achieve these goals using fairly conventional op amp
techniques. Your most critical points would be clean level boost on your
inputs, I would jack the incoming signal up to a couple of volts, with a +-
10 volt signal path you have very high headroom compared to the noise floor
you just have to be careful not to overdrive this signal path.

For instance if you want to mix 4 inputs into the one buss do not exceed 1/4
of the total clean headroom available on the buss. For a range of +- 10
volts the leaves +- 2.5 volts.

Alternately:

If you are tiring to mix an arbitrary number of channels I would run each
channel at high levels and Divide Down at the mix point, for instance if you
have 20 channels running at the +- 10 volt max, divide each by 20. This
would work best if the Divide is actively based on the number of channels in
use.

If all your mixing operations are performed at higher signal levels it can
stay pretty clean. Of course it is still important to keep your circuitry
design operating with low distortion and a low noise floor but it is not
hard to select good Op Amps for this type design. A lot of old mixing
console designs did not have the better "cleaner" component options we have
today

- Jerry