FMco

ALM Busy Circuits 8HP
OSCILLATOR VCO ENVELOPE VCA MIXER

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Compact 2-operator FM voice with direct and CV control over index, ratio, and waveform selection, triggerable decay envelope, chord mode with inversion, encoder tuning, and stereo-widened outputs.

Patch Ideas · 5

★ FM bell
Tune to the song root · Ratio locked to a clean harmonic interval · short trigger into Trig · low Index for the attack and a little more depth on sustain · glassy bell strikes without extra envelopes.
▸ Show diagram
Patch diagramPatch diagram with 3 modules and 4 connections. Modules: FMco, Sequencer, Output. Signals: 2 audio, 1 pitch, 1 gate.FMcoSequencerOutputTune: root noteRatio: lockedFM Index: lowTriggateChord CV1v/octOUT LaudioOUT RaudioGategateCV1v/octLaudioRaudioaudiopitchgate
★ Chord stab
Chord mode on · inversion stepped from a sequencer CV lane · each trigger opens the decay envelope and lets the voice hit like a one-module chord machine.
▸ Show diagram
Patch diagramPatch diagram with 3 modules and 3 connections. Modules: FMco, Sequencer, Output. Signals: 1 audio, 1 pitch, 1 gate.FMcoSequencerOutputChord: onTune: root noteTriggateChord CV1v/octOUT LaudioGategateCV1v/octInaudioaudiopitchgate
★ Index sweep lead
A slow LFO into Index CV · Ratio stays locked · Wave set bright · the same note blooms from clean to clangorous as the envelope decays, which makes one voice cover both lead and percussion duties.
▸ Show diagram
Patch diagramPatch diagram with 4 modules and 4 connections. Modules: FMco, LFO, Output, Sequencer. Signals: 2 audio, 1 cv, 1 gate.FMcoLFOOutputSequencerWave: brightRatio: lockedIndex CVcvTriggateOUT LaudioOUT RaudioOutcvLaudioRaudioGategateaudiocvgate
Wave-morph drone
Hold a chord with long gates · LFO into Wave CV and Ratio CV · the voice morphs through operator shapes while keeping pitch anchored by Tune · a compact evolving drone that does not need extra oscillators.
▸ Show diagram
Patch diagramPatch diagram with 4 modules and 5 connections. Modules: FMco, LFO, Sequencer, Output. Signals: 2 audio, 2 cv, 1 gate.FMcoLFOSequencerOutputChord: onTune: stable rootTriggateWave CVcvRatio CVcvOUT LaudioOUT RaudioOutcvGategateLaudioRaudioaudiocvgate
Percussive FM split
Short gates to Trig · Chord CV sequenced over a small range · Index stays modest while Ratio moves aggressively · the left and right outputs widen the transient enough to sit in a mix without an external stereo processor.
▸ Show diagram
Patch diagramPatch diagram with 4 modules and 5 connections. Modules: FMco, Sequencer, Mixer, Output. Signals: 3 audio, 1 pitch, 1 gate.FMcoSequencerMixerOutputRatio: freeFM Index: modestTriggateChord CV1v/octOUT LaudioOUT RaudioGategateCV1v/octLaudioRaudioOutaudioInaudioaudiopitchgate

Behaviors

Triggerable voice patch Trig

The built-in decay envelope is internally tied to FM depth and output level, so one gate makes the module act like a complete voice.

2-operator FM move Index and Ratio

Manual and CV control over the FM pair gives a broad range from smooth harmonic tones to metallic inharmonic sidebands.

Chord mode enable Chord

Chord mode provides CV-controlled four-voice harmony with inversion, turning the module into a compact chord voice rather than a single-note oscillator.

Stereo widening use OUT L and OUT R together

The final output widens the image, so the module reads as a finished voice instead of a hard-center mono source.

Waveform selection switch Wave selection

Eight operator wave shapes are available, letting the same FM structure shift between soft, bright, and more angular spectral content.

Controls

Global Tune Encoder-based tuning control for accurate pitch setting.
encoder tuning
Operator section FM Index Sets FM depth. Responds to direct and CV control.
attenuverting CV input
Operator section Ratio Sets operator ratio, with a lock switch for free or precise ratios.
free / locked
Operator section Wave Selects from the available operator waveforms.
8 classic operator shapes
Global Chord Enables four-voice chord mode with inversion control.
up to 4 voices

I/O

IN · 5

  • Trig trigger GATE
    Triggers the built-in decay envelope, which drives both FM depth and output level.
  • Index CV CV CV
    Voltage control over FM depth.
  • Ratio CV CV CV
    Voltage control over operator ratio.
  • Wave CV CV CV
    Voltage control over the operator waveform selection.
  • Chord CV CV CV
    Voltage control over chord mode and inversion.

OUT · 2

  • OUT L audio AUDIO
    Left stereo-widened audio output.
  • OUT R audio AUDIO
    Right stereo-widened audio output.