FM keys — a six-voice FM synth for dusty sounds

I really like this synth for its mellow keys, piano-esque/organ-y stuff, but it can also do abrasive FM things as well — it all really depends on the frequency relationship between the oscillators used (in this patch and all FM patches — harmonics, like fifths and octaves will create smoother, more harmonic content while frequencies that aren’t part of the harmonic series will create more abrasive, inharmonic sounds).

FM synthesis can get kind of gnarly and overly complicated, and I wanted to create a patch that had character but was relatively easy to use, so FM keys.

The patch uses two operators (sine wave oscillators) per voice. They are arranged so that the carrier (the oscillator that is heard) feeds back into the modulator (the oscillator that variably modifies the carrier), which is a simple way to create a lot of harmonic content.

After this, there are a few, basic effects to add “vibe”: vibrato (that one seems obvious, given the introduction), tremolo, and a “noise mod.”

The output is stereo via a stereo spread.

The patch responds to velocity and aftertouch (more on this later).

The default MIDI channel is 1 (MIDI modules can be found on the second and last used page of the patch).

This patch requires firmware 2.0. (



Left, latching — turns the tremolo off and on

Front page:

Across the top if a pretty LIGHT SHOW, which demonstrates when each voice is playing (and how loud it is; it responds to velocity and to the tremolo). Nice!

The next row has the MMOD OFFSET and MOD DEPTH. These control the timbre of the patch. As I mentioned in the introduction, setting this to harmonic ratios will produce smoother sounds, while inharmonic ratios will produce more abrasive sounds. Velocity affects the VCA but it also the mod depth; the result is that the harder you play, the louder and brighter the sound will be. There is also a MOD FINE TUNE control, which adjusts the frequency of the modular +/- a little over one semitone, because my favorite sounds are ever so slightly detuned harmonics (especially at an offset of 0 — beautiful, phased sounds).

The next row are the ADSR controls: ATTACK, DECAY, SUSTAIN, RELEASE. The envelope controls both the carrier VCA — how the volume of the synth’s output sounds — but also the VCA which feeds the modulator into the carrier. The envelope is exponential, which gives it a more “percussive” feel, but this may also result in the attack phase taking longer than you might expect to ‘swell’ in, and it also means that the sustain level will rise exponentially, so you may have to raise the sustain level higher than you would expect to get the result you want.

On the fourth row: The NOISE MOD can be used to add more dustiness to the sound; it modulates the oscillator frequencies via a random module (digital noise). I added the AFTERTOUCH RATE because the MIDI keyboard I was building this with (an Arturia Keystep 37) has a pretty steep aftertouch gradient, which means aftertouch is kind of an off/on affair; this controls a slew limiter to smooth out the aftertouch and give it more of a swell. The aftertouch is routed to the mod depth.

The buttons on the right side of the fourth row: CARRIER VIBRATO and MOD VIBRATO relate to the controls directly below it, which set the RATE for the vibrato. The depth of the vibrato is controlled via the mod wheel (CC1), but the range is set by the VIBRATO RANGE control.

On the bottom left of the fifth row are the tremolo controls, TREMOLO SPEED and TREMOLO DEPTH. The tremolo is turned off and on by the left stompswitch, with a pixel lighting up to show it is in use. The tremolo is also a slightly swung sine, which makes it feel ever so slightly off (in a good way).

Finally, there is a PITCHBEND RANGE for setting the range of the pitchbend. Interestingly, the pitchbend contributes even more to the “dusty” sound of the synth: it can sound a lot like a tape speeding up and slowing down.

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  • Category: Sound Synthesizer
  • Revision: 1.0
  • License: Creative Commons Attribution Share Alike 4.0
  • Views: 300
  • Modified: 2 weeks ago
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One comments on “FM keys — a six-voice FM synth for dusty sounds
  • Josh Cole on said:

    beautiful patch man, im a long time FM fan. and being able to gig with this instead of a dx7 or something. a dream

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