KnacK is a music composition framework for the ChucK programming language. It encourages organization of components in a standard way, enabling easier re-use in later projects.

It was originally developed by Colin Sullivan during the Music 220A course at Stanford’s CCRMA.


KnacK is divided into 3 main components:


An “Instrument” in KnacK is meant to encapsulate all unit generator functionality, and hide away anything that has to do with raw signal processing. The obvious exception here is if control over a ugen parameter is to be given to the “Performer” of the instrument.


A “Performer” in KnacK is the place where performance code is written, which can be anything from a general Arpeggiator which can play any Instrument subclass, to a performer of a specific instrument which manipulates specific parameters.


A “Score” in KnacK is a way to handle the high level transitions and events in a piece. A Score subclass is meant to be instantiated once, and is the entry point for the program.


I have spent some time thinking about event handling, and how this can be used to allow Performer and Instrument instances to react to high-level “aesthetic” data. The idea here is that the composer can have high-level metrics such as “darkness” or “density”, which can be modified in the score directly, and all Instrument and Performer classes can react accordingly. I am still in the process of determining the best way to accomplish this using function objects (I am used to functions as first class values), but some code can be found in lib/aesthetic/ and examples/MajorToMinor/.

Overview of the entities in KnacK

Basic Example

Consider the following simple example (can be found in examples/otf/. We have a DistortedKick which simply plays the DistortedKick.aif file when the playNote method is called:

* @class A distorted kick sampler.
* @extends Instrument
public class DistortedKick extends Instrument {

SndBuf clip;
string sampleDirectory;
if(me.args() == 0) {
"./" => sampleDirectory;
else {
me.arg(0) => sampleDirectory;
clip => outputsAll;
fun void playNote(float onVelocity) {
clip.length() => now;


Then there is a BoringKickPerformer which instantiates a DistortedKick, and plays it on each beat.

* @class Basic performer that plays a kick drum
* on each beat at a given speed.
* @extends Performer
public class BoringKickPerformer extends Performer {
DistortedKick kick;
* Play kick after each `noteDuration` amount
* of time.
fun void play() {
this.pre_play(); // super
while(true) {
spork ~ kick.playNote(1.0);
this._noteDuration => now;


To combine in a Movement of a score, we can instantiate this player, and tell it how frequently to play.

class OtfDemo extends Score {
BoringKickPerformer kickPerformer;
class BoringIntro extends Score.Movement {
fun void play() {
this.score() $ OtfDemo @=> OtfDemo @ score;

spork ~;
BoringIntro intro;
intro.duration(this.quarterNote*4*2); // Play for 2 bars


Then when an OtfDemo object is instantiated, and play is called on it, we will hear our beat play for the duration specified.