Boots the synth in an AudioWorklet and plays a MIDI file through it in realtime. You need ROMs extracted from your own MU2000 (see Preparing the ROMs); they are stored locally in your browser and never uploaded anywhere.
Picked ROMs are stored locally in this browser.
Fast synth plays back lighter (exact emulation needs a very powerful PC). Takes effect when the synth boots and locks afterwards.
Picking another file while playing replaces the song immediately.