New DIY FM Synth, XFM2, Offers 64-Voice Polyphony, Effects Engine

The XFM2 Synthesizer Module is a DIY 64-voice, 2-part, 6-operator FM Synthesizer with built-in effects processor, built on an FPGA chip.

The synth is based on two pre-assembled development boards: the Digilent CMOD A7-35T (FPGA, USB, SRAM) and the Adafruit UDA1334A (DAC). This combination means that the module has lets than 10 components and can be built for about $99.


  • 2-part, 64-voice polyphony (32-voice for each part)
  • Polyphonic/Monophonic Legato modes
  • The two parts can work as individual synthesizers, or layered
  • 6 operators per voice
  • 2 independent oscillators on each operator
  • 8 waveforms per operator
  • Variable modulation algorithm (extended from XFM to allow for multiple feedback loops)
  • A 7-segment, loopable Envelope Generator for each operator
    (DAD1D2SR1R2, with time and level controls for each segment)
  • 7-segment loopable Pitch Envelope Generator
  • Per-voice LFO with Triangle, Square, Sine, Random waveforms
  • Per-operator adjustable LFO sensitivity for pitch and volume
  • Per-operator adjustable velocity tracking, keyboard tracking
  • Polyphonic /Monophonic portamento
  • Pitch bend range adjustable independently for up and down directions
  • Extensive MIDI implementation (pitch bend, mod wheel, aftertouch, sustain pedal, breath ctl, foot ctl, volume, pan, chorus, reverb, delay, tremolo, etc.)
  • Four per-program assignable Performance Controls, which allow any parameter to be controlled by MIDI continuous controls messages.
  • All synthesizer and effects parameters (300+) adjustable via MIDI system exclusive messages.
  • Two complete stereo-in/stereo-out effect processors (one per part), including:
    • Decimator
    • Bitcrusher
    • Filter
    • Chorus/Flanger
    • Phaser
    • Amplitude Modulator
    • Delay
    • All of above effects can be run simultaneously, for both parts
  • Stereo Reverb with individual sends per part
  • Arpeggiator
  • 128 programs memory (EEPROM)
  • MIDI in, optional thru
  • Samplerate-grade modulations
  • 24-bit stereo analog out
  • Optional Stereo, 24-bit SPDIF digital out
  • Battery friendly, low power operation
  • Fully programmable (connecting it to a PC via USB)
  • Nearly zero latency (< 0.5ms)
  • Extremely fast boot time (< 100ms)

See the project site for detail

7 thoughts on “New DIY FM Synth, XFM2, Offers 64-Voice Polyphony, Effects Engine

  1. I wonder if this will be able to import patches / presets / banks from the DX7, like Dexed, FM7 etc. can?
    – or maybe a cross-conversion tool to do so.

    1. Agreed. I was thinking it would be nice to see a good sample-player with key/vel-maps, multi-mode filters, good mod rates and envelopes with curves. Would require more RAM, and a micro SD reader.

  2. These look like good specs, but I’m always annoyed to see only 1 LFO per voice. Why is it that the vast majority of past and present FM synths are always limited to 1 LFO? I love FM for creating evolving soundscapes and 1 LFO isn’t just enough.

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