Understanding Signal Flow

In Quiver, signals flow through modules following the conventions of hardware modular synthesizers. Understanding these conventions is key to creating patches that behave predictably.

Voltage Ranges

Quiver models its signals on the Eurorack standard:

graph LR
    subgraph "Audio Signals"
        A[±5V Peak<br/>AC-coupled]
    end
    subgraph "Control Voltage"
        B[0-10V Unipolar]
        C[±5V Bipolar]
    end
    subgraph "Pitch"
        D[1V/Octave<br/>0V = C4]
    end
    subgraph "Triggers/Gates"
        E[0V Low<br/>+5V High]
    end

    style A fill:#4a9eff,color:#fff
    style B fill:#f9a826,color:#000
    style C fill:#f9a826,color:#000
    style D fill:#e74c3c,color:#fff
    style E fill:#50c878,color:#fff

Audio Signals

Audio oscillates between -5V and +5V:

$$\text{audio}(t) \in [-5, +5]$$

This matches Eurorack levels and allows headroom for mixing.

Control Voltage (CV)

Two types of control voltage:

Volt-per-Octave (V/Oct)

Pitch follows the 1 Volt per Octave standard:

$$f = f_0 \cdot 2^{V}$$

Where $f_0 = 261.63$ Hz (C4) at 0V.

Gates and Triggers

sequenceDiagram
    participant G as Gate
    participant T as Trigger

    Note over G: Gate (sustained)
    G->>G: 0V (off)
    G->>G: +5V (on, held)
    G->>G: +5V (still on)
    G->>G: 0V (off)

    Note over T: Trigger (impulse)
    T->>T: 0V
    T->>T: +5V (1-10ms pulse)
    T->>T: 0V

• Gate: Sustained high signal (key held down)
• Trigger: Brief pulse (≈1-10ms) to start events

Signal Types in Code

Quiver tracks signal types through SignalKind:

pub enum SignalKind {
    Audio,           // ±5V AC-coupled
    CvBipolar,       // ±5V control
    CvUnipolar,      // 0-10V control
    VoltPerOctave,   // 1V/Oct pitch
    Gate,            // 0V or +5V sustained
    Trigger,         // 0V or +5V brief pulse
    Clock,           // Regular timing pulses
}

The type system helps catch mismatches:

// This will warn: connecting audio to a V/Oct input
patch.connect(vco.out("saw"), another_vco.in_("voct"))

Module Input Behavior

Input Summing

Multiple cables to one input are summed:

flowchart LR
    LFO1[LFO 1] -->|+2V| SUM((Σ))
    LFO2[LFO 2] -->|+3V| SUM
    SUM -->|+5V| VCF[VCF cutoff]

This models analog behavior where multiple CVs combine.

Attenuverters

Many inputs support attenuation and inversion:

// Half strength, inverted
patch.connect_with(
    lfo.out("sin"),
    vcf.in_("cutoff"),
    Cable::new().with_attenuation(-0.5),
)?;

The attenuverter range is typically -2 to +2, allowing inversion and some gain.

Normalled Connections

Some inputs have default sources when unpatched:

flowchart LR
    LEFT[Left Input] --> NORM{Unpatched?}
    NORM -->|Yes| RIGHT[Uses Left<br/>signal]
    NORM -->|No| EXT[External<br/>source]

The StereoOutput module, for example, normalizes right to left if right is unpatched.

Processing Order

Quiver automatically determines processing order through topological sort:

flowchart TD
    VCO[1. VCO] --> VCF[2. VCF]
    LFO[1. LFO] --> VCF
    VCF --> VCA[3. VCA]
    ENV[1. ENV] --> VCA
    VCA --> OUT[4. Output]

Modules with no dependencies process first. The algorithm (Kahn’s) ensures every module has its inputs ready before processing.

Common Patching Patterns

Modulation

flowchart LR
    LFO[LFO] -->|mod| TARGET[Target Parameter]
    OFFSET[Offset] -->|base| TARGET

Combine a static offset with an LFO for “center + modulation” control.

Envelope Following

flowchart LR
    AUDIO[Audio In] --> VCA[VCA]
    AUDIO --> ENV[Envelope<br/>Follower]
    ENV -->|level| VCA

Use audio amplitude to control other parameters.

FM (Frequency Modulation)

flowchart LR
    MOD[Modulator<br/>VCO] -->|fm| CARRIER[Carrier<br/>VCO]
    CARRIER --> OUT[Output]

Audio-rate modulation of oscillator frequency creates complex timbres.

Next: The Quiver Philosophy