Modulation System

How parameters are modulated in bbx_audio.

Overview

Modulation allows parameters to change over time:

• LFO modulating pitch → vibrato
• Envelope modulating amplitude → ADSR
• LFO modulating filter cutoff → wah effect

Control Rate vs Audio Rate

bbx_audio uses control rate modulation:

Most musical modulation is below 20 Hz, well within control rate capabilities.

Modulation Flow

1. Modulator block processes (LFO, Envelope)
2. First sample collected as modulation value
3. Target block receives value in modulation array
4. Block applies value to parameters

#![allow(unused)]
fn main() {
fn collect_modulation_values(&mut self, block_id: BlockId) {
    if has_modulation_outputs(block_id) {
        let buffer_index = self.get_buffer_index(block_id, 0);
        let first_sample = self.audio_buffers[buffer_index][0];
        self.modulation_values[block_id.0] = first_sample;
    }
}
}

Parameter Type

#![allow(unused)]
fn main() {
pub enum Parameter<S: Sample> {
    Static(S),              // Fixed value
    Modulated(BlockId),     // Controlled by modulator
}
}

Routing Modulation

Use the modulate() method to connect modulators to parameters:

#![allow(unused)]
fn main() {
// Create LFO (frequency, depth, waveform, seed)
let lfo = builder.add(LfoBlock::new(5.0, 0.5, Waveform::Sine, None));

// Create oscillator
let osc = builder.add(OscillatorBlock::new(440.0, Waveform::Sine, None));

// Connect modulation
builder.modulate(lfo, osc, "frequency");
}