Parameters and modulation

Almost every argument in the library is a Param. A Param is one of three things:

• A number: a constant value, 800 or 0.4.
• A sound: another Sound, evaluated sample by sample. This is audio-rate modulation.
• A function of time: Fn(t => ...) or a Func<double, float> in a project.

You never need to name the type. Pass whichever is convenient.

A number

// The filter sits at a fixed 800 Hz.
Saw(110).LowPass(800, q: 2) * 0.4

A sound

The modulating sound runs at audio rate: its value changes on every sample, not once per block.

// A slow sine sweeps the filter cutoff between 200 Hz and 2 kHz.
Saw(110).LowPass(Sine(0.25).Range(200, 2000), q: 4) * 0.4

Range(min, max) maps a sound from its own -1 to 1 onto a new span. Use it to turn an oscillator into a usable control.

Frequency modulation

A sound given as a frequency gives frequency modulation (FM). This is true FM: the phase follows the instantaneous frequency on every sample.

// A 220 Hz carrier, pitch-wobbled by a 440 Hz modulator, 300 Hz deep.
Sine(220 + Sine(440) * 300) * 0.4

The modulator's frequency sets the sideband spacing, and its depth sets how bright the sound is. Multiply the modulator by a larger number to brighten it.

A function of time

// A saw whose cutoff follows a formula: 800 Hz with a 600 Hz swing.
Saw(110).LowPass(Fn(t => 800 + 600 * Math.Sin(t)), q: 2) * 0.4

Combining modulators

A parameter can take a sound that is itself modulated, and that sound can have its own modulators.

// The filter's own cutoff is wobbled by a slower sine, while the saw is pitch-modulated too.
var wobble = Sine(0.2).Range(400, 1600);
Saw(110 + Sine(3) * 2).LowPass(wobble, q: 3) * 0.4

Things to know

• Frequencies are in hertz. An oscillator at 0.25 Hz is an LFO, not a sound.
• Modulators are sounds, so they cost CPU. A constant costs nothing; a sound used as a parameter runs its own graph.
• Range keeps the shape. A sine from -1 to 1 becomes a sine between the new bounds, not a different wave.