Tuesday, June 16, 2015

Another way to adjust level for ABX

Before being converted to (or back to) analog, my system runs digital signals through several processors: the Tact RCS 2.0 (I don't use the RCS, but this is a most useful device anyway with digital selection and volume control), and, in parallel, two Behringer units, one is a 2496 DCX and the other is a 2496 DEQ.

The midrange section runs through the DEQ, and the DEQ has a midi control feature which lets you select presets.  So all I need to do is have two presets which set the overall gain differently but are otherwise identical, and use midi to switch the presets exactly when the amplifiers are being switched.

It wouldn't be a bad idea at all if all ABX switching units were also midi triggered.  Midi was designed for doing stuff like this.  The typical way of controlling amplifiers with a  12V DC trigger signal is relatively limited.

Quite awhile ago, when I first got the QSC ABX box, I did something very much like this.  I used the ABX box to switch a DC signal on and off.  The I bought a midi controller box which triggered a pre-programmed midi signal when an voltage changes.  I programmed the DEQ with a "normal" program and a "reversed polarity" program, which could be selected by the midi transmitted by the midi box.  Then I could switch polarity by remote control.  All I'd need to add to this would be to trigger another function to change the amplifier relays at the same time.

I remember the sense of accomplishment at getting it all to work, but little else.  I did not find polarity to be particularly audible in ABX testing, and put very little effort into testing after the challenging equipment setup was done.  And so it often goes…

But anyway, controlling levels this way means no signal degrading attenuation box, no worries about high frequency roll off or phase shift, no worries about microphonic or noisy potentiometers, etc.

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