rust-synth

Terminal modular ambient synthesizer. Long cinematic Zimmer-style pads, drones, kick patterns and evolving textures — driven by math formulas (sigmoid, perlin, euclidean, golden ratio, game of life) inside FunDSP closures. No GUI, no DAW. Ratatui TUI on top of cpal audio output.

Install

macOS — Homebrew (Apple Silicon)

brew install fortunto2/tap/rust-synth
rust-synth

Build from source (any platform)

git clone https://github.com/fortunto2/rust-synth
cd rust-synth
cargo run --release

Or via Homebrew --head to build from latest main:

brew install --head fortunto2/tap/rust-synth

What it does

• 8 pre-allocated voices, 4 active by default: Pad, Bass, Heartbeat (kick), Sub Drone. Activate more with a — picks a golden-ratio frequency relative to existing tracks.
• 5 preset kinds: Pad · Drone · Shimmer · Heartbeat (3-layer kick drum) · Bass (sustained groove).
• 16-step Euclidean drum sequencer per track. hits + rotation sliders produce musically coherent patterns — any random combination is already a valid groove.
• Per-track LFO routable to cutoff, gain, freq (vibrato) or reverb.
• Valhalla-Supermassive-inspired reverb send per track. Two cascaded FDN reverbs with chorus between — 28-second tail with stereo modulation.
• Game of Life grid coupled to audio both ways. Each track's row gets seeded with alive cells per beat; row density continuously modulates that track's gain. Every 8 beats the row with the lowest density triggers genetic mutation of the weakest track.
• Genetic evolution: freq snaps to golden pentatonic, cutoff drift, pattern hits/rotation mutate too. Keys e / E / x for manual mutate / mutate-all / crossover.
• Master bus: high-shelf @ 3.5 kHz + lowpass + limiter, all driven by one brightness slider.
• Preset save/load (TOML, human-readable).
• Master recording to FLAC 24-bit in a background thread.
• Live formula pane — see the math of the current preset with your live param values substituted.
• Trajectory forecast — plots the next 16 seconds of amplitude / cutoff / pulse curves based on current settings.
• Pixel-art Life grid, scope oscilloscope, 16-step pattern grid with play-head cursor.

Controls

Global

Tracks pane (left)

Params pane (right)

11 params per track: gain, cutoff, resonance, detune, freq, reverb, supermass, pulse, lfo rate, lfo depth, lfo tgt (OFF · CUT · GAIN · FREQ · REV).

Presets — the math

PadZimmer

osc(t) = Σ Aₖ · sin(2π · f · rₖ · t)          rₖ = [1, 1.501, 2.013, 3.007]
cut(t) = cutoff · (1 + 0.10 · phrase_wobble)  (+ optional LFO ±1 oct)
y = Moog(osc, cut, q) ⇒ HPshelf(3k, −3.5 dB)
       ⇒ chorus_L | chorus_R ⇒ hall(18m, 4s) ⇒ supermass_send

BassPulse

osc = 0.55·sin(2πft) + 0.22·sin(4πft) + 0.35·sin(πft)
y = Moog(osc, min(cut, 900Hz), min(q, 0.65))
  · groove(t)           groove = 0.45 + 0.55·e^(−3.5·φ)
  ⇒ hall(14m, 2.5s) ⇒ supermass_send

Heartbeat (3-layer kick, step-gated)

body   = sin(2π · f·(0.7 + 1.5·e^(−40·φₛ)) · t)  · e^(−4·φₛ)   on active step
sub    = sin(π · f · t)                            · e^(−1.5·φₛ) on active step
click  = HP(brown, 1.8 kHz)                       · e^(−40·φₛ) on active step

where active = (euclidean_bits(hits, rotation) >> step) & 1
      step   = (t · bpm/60 · 4) mod 16           (16th-note resolution)
      φₛ     = fract(t · bpm/60 · 4)             (phase within the step)

DroneSub

sub(t) = 0.45·sin(π·f·t) + 0.12·sin(2π·f·t)
noise  = Moog(brown(t), clip(cut, 40..300), q)
am(t)  = 0.88 + 0.12·½(1 − cos(2π·bpm/60·t))
y = (sub + 0.28·noise) · am ⇒ hall(20m, 5s) ⇒ supermass_send

Shimmer

y = HP(0.18·sin(4πft) + 0.12·sin(6πft) + 0.08·sin(8πft), 400 Hz)
  ⇒ hall(22m, 6s) ⇒ supermass_send

Master bus

stereo_sum
  ⇒ highshelf(3.5 kHz, q=0.7, gain = 0.2..1.0)      ← driven by brightness
  ⇒ lowpass(cutoff = 3k..18k, q=0.5)                 ← driven by brightness
  ⇒ limiter_stereo(1 ms attack, 300 ms release)
  ⇒ cpal

Architecture

src/math/
  sigmoid.rs   smoothstep, sigmoid, softexp, ease
  pulse.rs     beat_phase, pulse_decay, phrase_phase (f64 for multi-hour stability)
  harmony.rs   PHI, golden_freq, golden_pentatonic, xorshift RNG
  rhythm.rs    16-step Euclidean bitmask (Bjorklund-style)
  life.rs      Conway's Game of Life (toroidal B3/S23)
  genetic.rs   Genome + mutate / crossover (snaps freq to golden pentatonic)
  rnd.rs       Perlin 1D, brown walk, value noise
src/audio/
  track.rs     TrackParams (Shared atomics) — lock-free audio/UI shared state
  preset.rs    5 preset graphs + LfoBundle + master_bus + supermass_send
  engine.rs    cpal setup, 8-track master graph, scope ring buffer
src/tui/
  app.rs       ratatui event loop + key bindings + Focus mode
  tracks.rs    left pane list
  params.rs    right pane 11 sliders
  formula.rs   live math with substituted values
  beats.rs     BPM beat grid + phrase progress
  pattern.rs   16-step Euclidean grid with play-head
  life.rs      chunky pixel-art grid (one row per track)
  waveform.rs  stereo oscilloscope (braille canvas)
  trajectory.rs  next-16-seconds envelope forecast
src/recording.rs   FLAC 24-bit via flacenc (background encode thread)
src/persistence.rs TOML preset save/load with serde defaults
cli/main.rs        offline WAV render mirroring default tracks

All long-running DSP state is f64 (FunDSP hacker module) so time counters stay precise for 100+ hours — hacker32 drifts around 5 min at 48 kHz.

Key invariants

• Audio callback never locks anything except a tiny scope ring-buffer mutex. All live params flow through FunDSP Shared atomics. Patterns use Arc<AtomicU32> loads (Relaxed).
• Resonance is capped at 0.65 in the audio path. Higher values would turn the Moog ladder into a self-oscillating sine wave at cutoff frequency — classic "whistle" bug.
• Supermass reverbs have damping ≥ 0.88. 28-second T60 with lower damping piles up 4–8 kHz resonances.
• Euclidean distribution guarantees musical patterns. Any random (hits, rotation) is already a valid groove — no cluster, no gap.

Building

Needs Rust 1.75+ and a working audio device.

make run          # release build + TUI
make dev          # debug build + TUI
make render       # 30 s offline WAV → out/render.wav
make integration  # 5 s smoke test
make check        # fmt + clippy -D warnings + test

Tests:

cargo test

19 tests cover the math layer end-to-end (Bjorklund, blinker oscillator, golden determinism, sigmoid/smoothstep range, FLAC encode roundtrip).

License

MIT. Made by @fortunto2 with help from Claude Code.