Coding audio components

audio:custom is the base type for audio components. You have access to most of the Processing API not related to graphical operations. This does not include functions not suitable for real-time operation (would normally be advised only in setup within Processing). You also have access to a range of audio processing blocks and related functions.

Unit Generators (UGens)

Like many other environments, audio processing is achieved by interconnecting a series of audio processing blocks, otherwise known as unit generators (UGens). Inside audio components these UGens are subclasses of Pipe, from the JAudioLibs Pipes library. This is the same routing library used throughout the audio pipeline in Praxis LIVE. There is no difference in performance between connections made in code or graphically - group things in the way that makes most sense to you!

Unit generators are created by placing the @UGen annotation on fields of the relevant types. Multiple fields of the same type may be annotated together -

@UGen Osc osc1, osc2;
@UGen IIRFilter filter;

Using annotations in this way, UGens of the same name and type are copied across as the code updates, ensuring glitch free playback while updating code.

See a full list of available UGens further down this page.

Per-sample functions

It is also possible to write per-sample processing, eg. by using the OpGen UGen and passing in a Function.

Input / Output

Audio input and output ports are defined by use of the @In and @Out annotations on fields of type AudioIn and AudioOut. These types are also subclasses of Pipe.

eg. -

@In(1) AudioIn in1;
@In(2) AudioIn in2;
@Out(1) AudioOut out;

You also have access to the same control input and output functionality as core components.

Key method hooks

The key method hooks you can override are -

  • setup() : called each time the pipeline is started and any time the code is updated. Because this method is called on code updates, it needs to be suitable for real-time usage. NB. All UGens will be reset and disconnected prior to this method being called
  • update() : called every update cycle before the next audio buffer is processed. If your component reacts solely to input and this method would otherwise be empty, remove it for efficiency.

Audio routing

Audio routing should usually be done inside the setup() method, although dynamic changes to the audio processing graph are possible. Note that some UGens, such as Gain, provide the ability to dynamically switch off parts of the audio graph for efficiency without a need for dynamic connections.

Prior to setup() being called, all UGens are disconnected from each other and all parameters are reset - this ensures that the routing always respects the code you write.

Be careful not to try and link ugens more times than they allow - most ugens only support one output, and zero or one input.

Pipe link(Pipe ... ugens)

Link the UGens together in a chain. For convenience the last UGen provided is returned (see example).


Add add(Pipe ... ugens)

Add the outputs of the provided UGens together. This method creates an Add UGen, and connects the provided UGens as sources. The returned UGen supports unlimited inputs and sources may be added later.


Mod mod(Pipe ... ugens)

Multiply the outputs of the provided UGens together. This method creates a Mod UGen, and connects the provided UGens as sources. The returned UGen supports unlimited inputs and sources may be added later.


Tee tee();

Construct a Tee UGen. The returned UGen supports an unlimited number of outputs. It is useful for splitting a signal into multiple chains, or creating feedback loops.

Example usage

The routing methods support nested and un-nested usage. Use whichever feels most comfortable.

@In(1) AudioIn in1;
@In(2) AudioIn in2;
@In(3) AudioIn modulator;
@Out(1) AudioOut out;

@UGen IIRFilter filter1, filter2;

public void setup() {
        link(in1, filter1);
        link(in2, filter2);
  // OR
  link(in1, filter1);
  link(in2, filter2);
  Add a = add(filter1, filter2);
  Mod m = mod(a, modulator);
  link(m, out);

Loading samples

Use the @P annotation on a field of type Table to support loading of samples from a file. Loading is done asynchronously.

The field value may be null - UGens will handle this, but be careful in your own code. Use the @OnChange annotation to update UGens with a new table -

@UGen Player player;
@P(1) @OnChange("updateSample") Table sample;

public void setup() {
  // rest of setup

void updateSample() {

Additional variables and functions

In addition to the core Processing API functions, a range of specific audio-related functions and variables are available to your code.

Samplerate and block size

double sampleRate;
int blockSize;

These variables provide access to the sample rate and block size (number of samples processed in one update). They should be treated as read-only.

Notes and frequency

double noteToFrequency(String note)
int noteToMidi(String note)
double midiToFrequency(int midi)

These methods convert from a MIDI note number or a text representation of a note (a4, f#3, etc.) into a frequency in Hz.

Available UGens

All built-in UGens support a fluid programming style. Property setters take a value and return the UGen. Property getters take no value and return the value of the property.

eg. -

IIRFilter filter;

double freq = filter.frequency();


A mono chorus effect. One input, one output.

@UGen Chorus chorus;

chorus.depth(double ms); // depth of chorus in ms, default 0
chorus.rate(double hz); // rate of chorus in hz, default 0 f); // feedback (0, none - 1, 100%), default 0

Comb Filter

A mono comb filter effect. One input, one output.

@UGen CombFilter comb;

comb.frequency(double hz); // frequency of filter in Hz, default 20Hz f); // feedback (0, none - 1, 100%), default 0


Mono delay effect, with maximum delay time of 2 seconds. One input, one output.

@UGen Delay delay;

delay.time(double s); // delay time in seconds (0..2), default 0 f); // feedback (0, none - 1, 100%), default 0
delay.level(double l); // level of delay (0, none - 1, 100%), default 1
delay.passthrough(boolean p); // whether to add input signal, default false


A mono or stereo reverb effect. One or two inputs, one or two outputs.

@Ugen Freeverb reverb;

reverb.damp(double d); // amount of damping (0..1), default 0.5
reverb.dry(double d); // level of dry signal (0..1), default 0.5
reverb.roomSize(double s); // room size, (0..1), default 0.5
reverb.wet(double w); // level of wet signal (0..1), default 0
reverb.width(double w); // width of stereo signal (0..1), default 0.5


Mono gain. One input, one output.

The level value is interpolated over buffer so suitable for envelopes. The level value is used as a linear multiplier. A level of 0 will result in input being switched off (no processing required).

@UGen Gain gain;

gain.level(double g); // value by which input is multiplied.

IIR Filter

A mono IIR filter with various types (LP6, LP12, LP24, HP12, HP24, BP12, NP12). Types are available as static fields - eg. use IIRFilter.LP12

@UGen IIRFilter filter;

filter.frequency(double hz); // frequency in Hz, default 20000
filter.resonance(double db); // resonance in dB (0..30), default 0
filter.type(IIRFilterOp.Type type); // filter type from list above, default IIRFilter.LP6


A low frequency oscillator with various waveforms (Sine, Square and Saw), and unipolar (0..1) or bipolar (-1..1) output. Unlike the Osc waveforms, these are not bandlimited. One output.

@UGen LFO lfo;

lfo.bipolar(boolean bp); // bipolar output, default false (unipolar)
lfo.frequency(double hz); // frequency in Hz, default 1
lfo.gain(double g); // linear gain of waveform (0..1), default 1
lfo.waveform(Waveform w); // waveform, one of SINE, SQUARE or SAW, default SINE

LFO Delay

A mono delay effect with delay time controlled by an LFO - similar to the chorus effect. One input, one output.

@UGen LFODelay delay;

delay.time(double s); // delay time in seconds (0..1), default 0 f); // feedback (0, none - 1, 100%), default 0
delay.range(double r); // range of lfo sweep (0..1), default 0
delay.rate(double hz); // rate of lfo in Hz, default 0

OpGen (function holder)

A mono UGen that allows a per-sample function to be applied. One (optional) input, one output.

@UGen OpGen op;

op.function(new Function() {
  public double process(double in) {
    return in;
}); // default is passthrough Function as shown.

Oscillator (Osc)

An oscillator with various waveforms (Sine, Square and Saw). The waveforms are bandlimited where necessary. One output.

@UGen Osc osc;

osc.frequency(double hz); // frequency in Hz, default 440
osc.gain(double g); // linear gain of waveform (0..1), default 1
osc.waveform(Waveform w); // waveform, one of SINE, SQUARE or SAW, default SINE


A simple mono overdrive effect. One input, one output.

@UGen Overdrive od; amt); // drive (0..1), default 0


A multi-channel sample table player. This UGen currently supports up to 16 outputs.

The output channel of the table is modulo the output channel of the UGen. eg. if a Player has three outputs and the table (sample) has two channels, then outputs 1 & 3 will both receive sample channel 1.

@UGen Player player;

player.table(Table t); // sample table to play or null, default null i); // loop in / start point (0..1), default 0
player.out(double o); // loop out / stop point (0..1), default 1
player.position(double p); // playback position (0..1), no default - not reset
player.speed(double s); // playback speed, default 1
player.looping(boolean lp); // whether to loop playback, default false; // start playing
player.stop(); // stop playing