This is an analogue/digital hybrid design to control a multi-channel bus in a Metric Halo interface equipped with +DSP by means of high quality analogue faders. So far this has been down using a ULN-8 with a Maihak W66c 130mm fader to control quadraphonic playback using 4 main outputs and 2 sub-bass outputs (summed for front left and right, and rear left and right).
An 8 channel bus is set up in the MIO Console, with crossovers and summing for the 4 audio channels to 6 discreet outputs. A sine wave at 1 kHz is output from channel 8, through the Maihak fader, and back into input 8. The signal is squared, smoothed, and square rooted and then used to control the output volume of outputs 1-6.
I used this setup as my mixing desk for the sound projection of Stockhausen's "Hymnen" at the Playfair Library, Edinburgh on 13th February 2015, which we believe to have been the Scottish Premiere.