- programmable 4-operator 8-algorithm digital fm tone generator - independent 5-parameter envelope generator for each operator - 32-voice internal ram memory - 128 voices programmed into internal rom - built-in cassette interface for voice data storage - single, dual, and split play modes - 32 performance memories can be programmed with voice combinations and other performance parameters - built-in stereo chorus effect (only dx-21) - 61-key keyboard - the dx21´s keyboard itself does not have key velocity, but its tone generator accept key velocity data from an external midi source - sustain footswitch, volume foot controller and breath controller inputs - midi in/out/thru terminals