The Yamaha DX21 is a synthesizer released by Yamaha in 1983. It is a four-voice polyphonic synthesizer with two digital oscillators and two analog oscillators per voice. It features a variety of sound-shaping controls, including an envelope generator, a low-pass filter, and an arpeggiator. The DX21 is capable of producing a wide range of sounds, from classic analog leads and basses to digital pads and sound effects.