I think you guys missed my point.
1st I have no objection to DMX at all. In fact, I really would like to use DMX, if for nothing else than to have some scenes/chases for the PAR's.
Alas, as a OMB as it is I have to do it all. I just don't have the bandwidth to be the MC, performer, soundman AND be the lighting guy as well. Plus, I'm budget constrained
So I'm keeping it simple. I just purchased two Tri-GEM's and an Aggressor. Both are sound activated only (non-DMX) with the added benefit of turning off when no sound is present. I still plan to 'control' them via foot switches so I can select between the Tri-Gems, the Aggressor or both.
Back to my idea though. I wasn't suggesting it would be simple to control a servo in time with a tempo. Nor was I suggesting that the fixture determine WHAT the BPM is. Indeed, for all the reasons all have mentioned that would be complex. Just determine the "BPM" (as defined by whatever 'bumps & thumps make the sound activation work now) crossed some pre-defined threshold.
i.e., that sound activation be 'intelligent' enough such that if the various bumps & thumps (again, that makes it work now) could decide those bumps/thumps were 'some longer time apart' then the light would simply start revolving instead of the normal 'frenetic' mode.
Take the Vertigo for example. In 'normal' mode the light responds to 'bumps & thumps' and (arbitrarily?) changes LED color and/or degree angle and/or direction of the revolving stepper. At least that's how it appears to me.
So, using the controller clock as a reference, count the cycles between the 'bumps & thumps' (that activate things now) and if it exceeds a certain count that equals a certain low BPM (again, not deciding precisely WHAT BPM it is as the threshold is already defined) then just instruct the stepper motor to do nothing but revolve slowly ala an ADJ Sparkle LED (or any other light that just rotates at a constant RPM).
Yes, it IS that simple. We're not talking about 'AI' controlling a moving head precisely to the beat of the music without human/DMX intervention. We're talking about a <$200 fixture that goes into 'rotation mode' when it gets slow/quiet (not too unlike the Tri-Phase).