8 operator FM synth with a cross-oscillator modulation matrix, available in VST3 and CLAP plugin formats. Oscillator generation and modulation is SIMD accelerated (via wide).

Open source under GPLv3.

In development, control ranges and such may change between versions, potentially breaking your presets/saved projects on update.

Downloads available at the releases page.

There are 8 feedback-capable sine oscillators, each with independent amplitude envelopes. Each of the 8 oscillators has the following controls:

• Amp: Direct output volume (post-modulation, doesn't affect modulation of other oscillators)
• Feedback: Oscillator tone/self-PM. Positive values tend towards a saw wave, negative values towards a square wave.
• Frequency Controls:
  • Coarse: Frequency shift in semitones
  • Fine: Frequency shift in cents
  • Frequency Multiply: Multiplies frequency by an integer value from 1-64
  • Frequency Divide: Divides frequency by an integer value from 1-64
• Envelope controls: (affects modulation)
  • Delay: Time before note starts.
  • Attack: Envelope attack time. How long it takes to reach maximum volume after note start.
  • Delay: Time note is held at peak after attack.
  • Decay: Envelope decay time. How long it takes for the volume to descend to the sustain level after attack + hold time.
  • Sustain: Envelope sustain level. Sustained volume level after decay stage but before note release.
  • Release: Envelope release time. Time note continues playing after note release.
  • Note: The decay and release stages are exponential, not linear.
• Misc. Controls
  • Velocity Sensitivity: How much MIDI velocity affects oscillator volume.
  • Keyscaling: How oscillator volume decreases/increases as pitch rises/falls.

The oscillators modulate each other via a 8x8 matrix, where every oscillator is connected to every other one. It is possible to create cross-oscillator feedback loops (e.g. Osc1 and Osc2 both modulate each other) but they don't typically sound that good (not that I'm stopping you). The matrix is implemented by enforcing a 1-sample delay between oscillators.

There is also a polyphonic multimode filter (Simper SVF), controllable via an ADSR envelope.

Technically this is a PM synth, but the terms PM/FM are often used interchangeably. If you want a modular-style (exponential-pitch) FM synth, it can be set up in Cardinal or Odin2 (though it sounds metallic and is difficult to tune).

Click and drag to adjust slider values. Double click to reset to default. SHIFT+drag for fine adjustments. Right-click or CTRL+click to type values in.

Made for fun. This is basically a Dexed clone, except:

• Build-your-own algorithm with the FM matrix
• Feedback on every oscillator
• DAHDSR envelopes
• 8 operators
• More wave types
• 32-bit floating point for all audio

After installing Rust, you can compile Foam as follows:

cargo xtask bundle foam --release

Thanks to Surge XT (and its developers) for the +/- FM feedback algorithm.

Thanks to NIH-plug for being a great plugin framework.

Thanks to Codeium for filling out a lot of the boilerplate which would have been a pain to do manually (mostly plugin parameters).

This project and all its files are licensed under the GPLv3 license.

The following file/s are additionally available under the ISC license (indicated in the file header)

• src/editor/param_slider.rs

• DSP:

  • Mono retrig and better portamento
  • Add noise source somewhere
  • Bandlimited oscillator toggle / multiple waves
    • AKA just turn it into a wavetable synth...
    • Switch to integer phase instead of float
  • Add LFO and pitch envelope
  • RM modulation
  • Mod matrix
  • Preset manager
  • Oversampling
  • Add panning
  • Click/drag points on graphical envelope
  • MSEG modulators
  • Envelope slope controls?
  • Toggle oscillators on/off
  • Allow use of the filter in FM modulation
  • Allow picking keyscaling root key
  • Linear & log keyscaling
  • Toggle oscillator keytracking
  • Scala support
  • 8/16/24 bit integer FM calcs from Dexed? (for speed)
  • Optimize
    • Enforce a minimum (constant?) block size

• GUI:

  • Highlight/bold From # and To # on mouseover
  • Add filter send to matrix
  • Use relative ParamSlider for FloatParams, absolute for EnumParams
  • Dropdown menus for EnumParams
  • Dark theme
  • Global oscilloscope / spectrogram
  • Resizable GUI

• Code:

  • Use more constants for GUI dimensions
  • Clean up

• Lofty Wishlist

  • Oscillator wavetables
  • MSEG modulators
  • Modulation of all parameters
  • Optional audio-rate/block-rate modulation
  • Effects
  • FM from/to sample player oscillator
  • 2 filters, more filter types.
  • Good presets
  • Add/remove oscillators
  • Configurable waveshaper on each fm connection

og pitch + matrix -> phase (0-1) -> phaseshaper (0-1) -> wave -> waveshaper -> matrix -> effects -> out

phaseshapers: powf, mseg, squeeze, sync, quantize, waveshapers: powf, mseg, asymmetric powf, linear fold, sine fold, linear wrap, effects: distortion, chorus, flanger, phaser, delay, reverb, compressor, eq, filter