MIDI compatible midi stands for musical instrument digital interface .....mean if you play any instrument and they were equipe with the in and out midi .........you could plug them in the roland and plug in your speaker system that box would control any effects you want to create echo reverb or delay .............so unless you have an instrument that you want to get echo ? midi was popular in the 80 s but now that we have computers ? about all it is good for is if you plug in a microphone and hook it up to a pa system to use for singing .......you could always plug the speaker output of your tv listen to your show with reverb effects lolllllllllllllllllll