Mbira said:I like this idea! This would be doable with my equipment. If I'm understanding, this would be like building a "feedback detector"?
While I don't know what this has to do with the original question.. here is how to do feedback detector.
http://www.google.com/patents?id=YrwaAAAAEBAJ&dq=john+roberts+visual+indication+of+feedback
Back in the '80s I did several midi control products (at Peavey) and we even sold a relay box that could be controlled by midi, surely this stuff is still out there. As I recall the relay box, hung off some other product so it was not a very cost effective solution, even if you could still find one.
JR