4-OP Sine Waves FM
DX21 generates sounds by combining 4 sine wave oscillators (called Operator) with Frequency Modulation (FM). 8 modulation routings (called Algorithm) can be selected.
This 4-Operator series can be seen as a simpler version of DX7 (6-operator).
While other 4-OP FM synth at that time and even 6-OP DX7 was mono-timbral, DX21 had the advantage of being bi-timbral.
DX21 is 8-polyphonic, and the voices can be separated into 4+4 voices in the 'DUAL' and 'SPLIT' modes.
Mono-timbral 4-OP-Sine-Waves FM synths use YM2151 OPM chip (FM Operator Type M).
DX21 uses the slightly updated version, YM2164 OPP chip, controlled by Hitachi HD63B03 CPU (A version of Motorola MC6800).
OPP seems to be the multi-timbral version of OPM.
DX21 is the rare DX synth that has a built-in analog quasi-stereo chorus.
DX21
Deep Synthesis: Home7. 4. 2005