What's going on here? (drum machine question)

[FranklinD]

Are both drum machines hooked up in sync with MIDI or something? : https://www.youtube.com/watch?v=vdIXOROUxW4
It looks like he's controlling one machine with the other as well... I'm sure this is a dumb question but I just wasn't aware these things could work in this way.
Same thing with this: https://www.youtube.com/watch?v=oLzFV93_rYI
He's going MIDI out from the ER1 and MIDI in to the Evolver?

 

[TexRoadkill]

Yep, that's part of what MIDI is about.