Your First Patch

Let’s build a complete synthesizer voice: an oscillator through a filter, shaped by an envelope. This is the classic subtractive synthesis signal path.

flowchart LR
    VCO[VCO] -->|saw| VCF[VCF]
    VCF -->|lowpass| VCA[VCA]
    ADSR[ADSR] -->|env| VCF
    ADSR -->|env| VCA
    GATE[Gate] -->|trigger| ADSR
    VCA --> OUT[Output]

The Complete Example

//! First Patch Example
//!
//! A complete subtractive synthesizer voice demonstrating the core
//! Quiver workflow: VCO → VCF → VCA with ADSR envelope shaping.
//!
//! Run with: cargo run --example first_patch

use quiver::prelude::*;
use std::sync::Arc;

fn main() {
    // CD-quality sample rate
    let sample_rate = 44100.0;

    // Create our patch (virtual modular case)
    let mut patch = Patch::new(sample_rate);

    // External control: gate signal for envelope triggering
    let gate_cv = Arc::new(AtomicF64::new(0.0));

    // Add modules to the patch
    let gate = patch.add("gate", ExternalInput::gate(Arc::clone(&gate_cv)));
    let vco = patch.add("vco", Vco::new(sample_rate));
    let vcf = patch.add("vcf", Svf::new(sample_rate));
    let vca = patch.add("vca", Vca::new());
    let env = patch.add("env", Adsr::new(sample_rate));
    let output = patch.add("output", StereoOutput::new());

    // Patch cables: signal flow
    // Gate triggers the envelope
    patch.connect(gate.out("out"), env.in_("gate")).unwrap();

    // VCO → VCF → VCA → Output (main audio path)
    patch.connect(vco.out("saw"), vcf.in_("in")).unwrap();
    patch.connect(vcf.out("lp"), vca.in_("in")).unwrap();
    patch.connect(vca.out("out"), output.in_("left")).unwrap();
    patch.connect(vca.out("out"), output.in_("right")).unwrap();

    // Envelope modulates both filter and amplitude
    patch.connect(env.out("env"), vcf.in_("cutoff")).unwrap();
    patch.connect(env.out("env"), vca.in_("cv")).unwrap();

    // Compile the patch for processing
    patch.set_output(output.id());
    patch.compile().unwrap();

    println!(
        "Patch compiled: {} modules, {} cables",
        patch.node_count(),
        patch.cable_count()
    );
    println!();

    // Play a note: gate on
    println!("Note ON - Gate rises to +5V");
    gate_cv.set(5.0);

    // Process attack phase (0.5 seconds)
    let attack_samples = (sample_rate * 0.5) as usize;
    let mut peak = 0.0_f64;

    for _ in 0..attack_samples {
        let (left, _) = patch.tick();
        peak = peak.max(left.abs());
    }
    println!("  Attack complete, peak level: {:.2}V", peak);

    // Release the note: gate off
    println!("Note OFF - Gate falls to 0V");
    gate_cv.set(0.0);

    // Process release phase
    let release_samples = (sample_rate * 1.0) as usize;
    let mut release_peak = 0.0_f64;

    for _ in 0..release_samples {
        let (left, _) = patch.tick();
        release_peak = release_peak.max(left.abs());
    }
    println!("  Release complete, final level: {:.4}V", release_peak);

    println!();
    println!("Subtractive synthesis voice complete!");
}

Understanding the Code

Creating a Patch

let mut patch = Patch::new(44100.0);

The Patch is your virtual modular case. The sample rate (44100 Hz = CD quality) determines timing precision for all modules.

Adding Modules

let vco = patch.add("vco", Vco::new(44100.0));
let vcf = patch.add("vcf", Svf::new(44100.0));

Each module gets a unique name and returns a NodeHandle. This handle lets you reference the module’s ports.

Making Connections

patch.connect(vco.out("saw"), vcf.in_("in")).unwrap();

The syntax mirrors real patching:

• vco.out("saw") — the sawtooth output jack
• vcf.in_("in") — the filter’s audio input jack

Note: We use in_() instead of in() because in is a Rust keyword.

Compiling the Patch

patch.set_output(output.id());
patch.compile().unwrap();

Compilation:

1. Performs topological sort (determines processing order)
2. Validates all connections
3. Detects any cycles (feedback loops)

Processing Audio

let (left, right) = patch.tick();

Each tick() advances the patch by one sample, returning stereo output.

Signal Flow in Detail

The envelope simultaneously controls:

• Filter cutoff — brighter attack, darker sustain
• VCA level — shapes volume contour

This dual modulation creates the characteristic “filter sweep” sound of analog synths.

What’s Happening Mathematically

The signal chain computes:

$$\text{output}(t) = \text{env}(t) \cdot \text{LPF}(\text{saw}(t), \text{env}(t) \cdot f_c)$$

Where:

• $\text{saw}(t)$ is the sawtooth oscillator at time $t$
• $\text{LPF}$ is the lowpass filter
• $\text{env}(t)$ is the envelope value
• $f_c$ is the base cutoff frequency

The envelope modulating both the filter and amplitude creates the classic synth timbre.

Experimenting

Try these modifications:

1. Different waveform: Change vco.out("saw") to vco.out("sqr") for a hollow, clarinet-like tone

2. Add an LFO: Modulate the filter for a rhythmic wobble

3. Change envelope times: Longer attack for pads, shorter for percussion

Next: Understanding Signal Flow