Envelopes & Modulators

Modulation sources shape how parameters change over time, creating movement and expression.

ADSR Envelope

The classic Attack-Decay-Sustain-Release envelope generator.

let env = patch.add("env", Adsr::new(44100.0));

Inputs

Outputs

decay and release are true segment durations — the envelope traverses its span in the set time regardless of the sustain level. The shape input toggles between linear and exponential curves.

Envelope Stages

Level
  5V ┤    ╱╲
     │   ╱  ╲____
     │  ╱        ╲
     │ ╱          ╲
  0V ┼╱────────────╲────
     A    D   S    R

Timing Curves

All stages use exponential curves:

Attack: \[ v(t) = 5 \cdot (1 - e^{-t/\tau_a}) \]

Decay/Release: \[ v(t) = (v_{start} - v_{end}) \cdot e^{-t/\tau} + v_{end} \]

Typical Settings

Envelope Follower

Extracts the amplitude envelope of an audio signal, with adjustable attack/release ballistics. type_id: envelope_follower.

let follower = patch.add("follow", EnvelopeFollower::new(44100.0));

Inputs

Outputs

PitchTracker

Pitch, gate and level from an audio signal: play a patch with a voice or an instrument. Pitch is estimated with YIN. type_id: pitch_tracker.

let mic = patch.add("mic", AudioInput::new(Arc::clone(&input)));
let track = patch.add("tracker", PitchTracker::new(44100.0));
patch.connect(mic.out("out"), track.in_("in"))?;
patch.connect(track.out("voct"), vco.in_("voct"))?;
patch.connect(track.out("gate"), env.in_("gate"))?;
patch.connect(track.out("level"), vca.in_("cv"))?;

Inputs

Outputs

Parameters

Accuracy and timing

Measured at 48 kHz and pinned by the module’s tests:

• A steady sine reads within ±1 cent anywhere in its band; with white noise 20 dB below it, within ±10 cents. A harmonic-rich tone (a band-limited sawtooth) reads within ±6 cents, worst near the band’s top. A tone with no fundamental reads right mid-band, but near a band’s top a weak or missing fundamental can read an octave low: pick the band so the notes sit below its top.
• Plucked and struck notes open the gate as promptly as held ones and read within 5 cents; a very fast decay at a low pitch reads a little sharp (11–13 cents for a 55 Hz pluck decaying in 50 ms). A swelling onset opens the gate at most 25 ms after an abrupt one.
• The gate opens on the first estimate whose analysis frame holds no silence before the onset, confirmed by the next frame, so the pitch is already right (±1 cent) when the gate rises. Opening takes 63.4, 48.0 and 40.8 ms (low, mid, high); closing after the sound ends, 28.4, 28.0 and 25.8 ms.
• After the gate falls the pitch holds within ±5 cents (±10 after a slow release) for notes two semitones or more above the band’s floor. In a band’s bottom two semitones a stop can leave it further off: up to ~40 cents after an abrupt stop (low band), ~25 after a fast release (high band).
• Broadband (white) noise alone does not open the gate. Brown or heavily low-passed noise, whose slow wander can look periodic within one frame, occasionally can.

The analysis is decimated and spread across ticks: about 100–300 ns per tick (0.5–1.4% of a core at 48 kHz), constant, with no allocation in tick or when the band changes.

LFO (Low-Frequency Oscillator)

See Oscillators for full documentation.

Quick reference:

let lfo = patch.add("lfo", Lfo::new(44100.0));
patch.connect(lfo.out("sin"), vcf.in_("fm"))?;

Sample and Hold

Captures input value on trigger pulse.

let sh = patch.add("sh", SampleAndHold::new());

Inputs

Output

Classic Use: Random CV

// Random stepped modulation
patch.connect(noise.out("white"), sh.in_("in"))?;
patch.connect(clock.out("div_8"), sh.in_("trigger"))?;
patch.connect(sh.out("out"), vcf.in_("cutoff"))?;

Slew Limiter

Limits rate of change—creates portamento and smoothing.

let slew = patch.add("slew", SlewLimiter::new(44100.0));

Inputs

Output

Applications

flowchart LR
    subgraph "Portamento"
        P1[Pitch CV] --> SLEW1[Slew] --> VCO1[VCO]
    end

    subgraph "Envelope Follower"
        P2[Audio] --> RECT[Rectify] --> SLEW2[Slew]
    end

    subgraph "Smooth Random"
        P3[S&H] --> SLEW3[Slew] --> MOD[Smooth CV]
    end

Quantizer

Snaps a V/Oct input to the nearest degree of a fixed scale. The scale is chosen at construction (not a port). type_id: quantizer.

let quant = patch.add("quant", Quantizer::major());
// Also: Quantizer::new(Scale::Dorian), Quantizer::chromatic(), Quantizer::minor()

Input

Output

Available Scales

Scale: Chromatic, Major, Minor, PentatonicMajor, PentatonicMinor, Dorian, Mixolydian, Blues. Change at runtime with quantizer.set_scale(Scale::Minor).

Scale Quantizer

A quantizer with CV-selectable root and scale, boundary hysteresis, a note-change trigger, and optional microtuning. type_id: scale_quantizer.

let sq = patch.add("sq", ScaleQuantizer::new(44100.0));

Inputs

Outputs

Microtuning (with the alloc feature)

// Install a custom scale from cents offsets within an octave:
sq_module.set_custom_scale(&[0.0, 200.0, 350.0, 700.0, 900.0]);

// Or load a Scala .scl file body:
sq_module.load_scala(scl_source)?;

Clock

Master timing generator.

let clock = patch.add("clock", Clock::new(44100.0));

Inputs

Outputs

Step Sequencer

8-step CV/gate sequencer.

let seq = patch.add("seq", StepSequencer::new());

Inputs

Outputs

Programming Steps

The sequencer holds 8 CV/gate pairs. In a full application, you’d set these via UI or MIDI.