Before I had just one single midi cable between my midi keyboard and the virus. (From midi out on the keyboard to midi in on the virus, of course).
But now the virus is also hooked up on its midi out. Every controller change you make, including turning of the cut off knob, is now transmitted through the midi interface and into the computer. But! it is also transmitted the other way back, from the computer through the midi interface and back to the virus. This way the Virus will get a sort of conformation about what you have just done with the controller knob.
Midi equipment, such as a synth, isn't just receiving midi commands about what to do. It also tells what it really does by sending midi information on the midi out.
This way you just not only send information to the synth, you will also get info back.
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It's a bit of like when you download something from the internet... Your computer isn't only receiving data. It also send info back to the server about witch filesize it has received etc. If there should be some difference this will be fixed. Without this "two-wayed" traffic almost every file you'd tried to download should be corrupt.
According to Access the problem with jumpy knobs is known, but not (as they say) "a really major problem". Maybe it's just basically because most Virus Racks are hokked up with decent midi interfaces, and this owners never experience the problems? Seemes pretty logical to me...
Like i said before. I don't fully understand exactly why it works, but now the problem seemes to be completely gone...