Operator VCV Rack module panel, a 6-operator DX7-style FM synth voice with voice selection and polyphonic output

Operator is a 6-operator FM synth voice in the Yamaha DX7 lineage. It loads DX7 .syx cartridges (or your own banks exported from Dexed), lets you pick a voice, and plays it polyphonically. The sound engine is Google’s music-synthesizer-for-android (msfa) DX7 core, so patches sound faithful to the original hardware: all six operators, every algorithm, feedback, key scaling, and the DX7 envelopes.

Out of the box it ships with four classic Brian Eno DX7 patches (transcribed from his Keyboard magazine charts, Feb 1987), so it makes sound the moment you patch a gate in.

Operator is 10 HP and polyphonic (up to 16 voices).

Quick start

Patch a polyphonic V/OCT and GATE from a sequencer or MIDI-CV module.
Turn the VOICE knob (or use the on-screen ◀ ▶ arrows) to audition patches.
Take AUDIO out: that’s the voice with its own DX7 envelope, ready to play.

To load your own sounds, right-click → Load bank (.syx)… and choose any DX7 32-voice cartridge. The original factory cartridges (and many more) are archived at Yamaha Black Boxes.

Controls

Control	Function
VOICE	Selects the patch within the current bank (0–31; the default Eno bank exposes 4).
BANK	Selects between loaded banks.
◀ / ▶ (on screen)	Previous / next voice.
TUNE	Coarse tune, ±12 semitones.
BRIGHTNESS	Tilts the whole timbre darker/brighter (−100%…+100%) by scaling modulator output: the DX7-style “one-knob” timbre control.
FEEDBACK	Offsets the patch’s feedback amount (−7…+7). Adds or removes the buzz/noise the feedback operator contributes.

Inputs

Input	Function
V/OCT	Pitch, 1V/oct, polyphonic. The channel count here sets the module’s polyphony.
GATE	Note on/off, polyphonic. Rising edge triggers the envelope; works with short triggers as well as sustained gates.
VEL	Velocity, polyphonic (0–10V). Sampled at note-on and applied via the patch’s velocity sensitivity.
VOICE CV	Voice select, 0–10V across the 32 voice slots.
BANK CV	Bank select, 1V per bank.
TUNE CV	1V/oct (adds to TUNE / V/OCT).
BRIGHTNESS CV	±5V over the full brightness range.
FEEDBACK CV	±5V over the full feedback-offset range.

Outputs

Output	Function
AUDIO	The voice with its internal DX7 envelope applied: a complete VCA-shaped note. Use this most of the time. Polyphonic.
VCO	The raw tone with no internal envelope, always sounding while a voice is held, so you can shape it with an external envelope/VCA (e.g. Vac, Swell, or OP ENV). Polyphonic.
ENV	An envelope follower of the audio amplitude, 0–10V, polyphonic: handy for ducking, side-chaining, or driving other modulation from the note’s loudness.

The display

The screen is a two-tab interface (tap the tabs at the top, Beat/Note style):

OPERATORS: shows the six operators laid out for the patch’s algorithm. Carriers (the operators you actually hear) are highlighted; modulators feed into them. Click an operator to mute/un-mute it, a quick way to hear what each one contributes or to thin a patch out. The algorithm number is shown too.
ENVELOPE: draws the selected voice’s carrier EG shape, with a live amplitude trace overlaid so you can see the envelope as it plays.

Banks & voices

Default bank: four Brian Eno DX7 patches. Because there are only four, the VOICE control is capped to those slots for this bank.
Load bank (.syx)…: load any standard DX7 32-voice cartridge, or a bank exported from Dexed. Multiple banks can be loaded; switch with BANK / BANK CV.
Remove current bank: drops the selected bank (available once more than one is loaded).
Loaded banks and the current selection are saved with the patch.

Notes on the engine

Faithful DX7 voicing: packed VMEM is read exactly as the hardware stores it (6 ops × 17 bytes + global + name), so cartridges play as intended, including algorithm, feedback, oscillator sync, key level/rate scaling, and the per-operator 4-stage envelopes.
Sample-rate-corrected envelopes: the DX7 EG rates are scaled to the host sample rate, so attack/decay times are correct at any sample rate.
Polyphony: driven by the V/OCT channel count, up to 16 voices. Released notes free their voice once their envelope decays below threshold.

Patch ideas

Classic FM keys. Sequence V/OCT + GATE polyphonically, take AUDIO, and audition voices with the VOICE knob. Add a touch of BRIGHTNESS movement with an LFO for an evolving timbre.

External envelope shaping. Take VCO instead of AUDIO and run it through Vac or Swell for a release/attack curve the original patch never had: turn a percussive DX7 patch into a pad, or vice versa.

FM as a sound source for OP ENV. Pair Operator with OP ENV: play the same DX7 voice on both, use Operator’s VCO for the tone and OP ENV for an authentic DX7 envelope you can offset and modulate independently.

Spectral dissection. On the OPERATORS tab, mute operators one at a time to hear how a patch is built: great for learning FM, and for stripping a busy patch down to a cleaner core.

Velocity dynamics. Patch a velocity source to VEL; patches with velocity sensitivity will open up their brightness and level as you play harder, just like the hardware.

Operator