hey guys
in this video:

you can see that there's a black plastic piece on the guitar right next to the output jack
and it looks like it has a knob on it or something

the thing is , i saw a local jazz fusion guitarist live once and he had the same thing on his guitar , and he used it to change his tone

so what is that thing ? and what does it do exactly ?
it the output for the midi pickup. the thin bar right by the bridge is the pickup, its the design roland uses.