Event an environment that represents an action

Inherits from: Object : Collection : Set : Dictionary : IdentityDictionary : Environment

Related classes: Pattern

An Event is an Environment that specifies an action to be taken in response to a play message. The key/value pairs within the Event specify the parameters of that action. Most methods, Event inherits from its superclasses, especially from Dictionary.

Basic Usage:

Events can be written as a series of key value pairs enclosed in parentheses.  Empty parentheses will create an empty event. They may be also used for object prototyping – Environment for more details.

Event as a name space for keeping objects:

Because of this simple syntax, Events are often used as name space for keeping objects:

// using an event to store values

q = (n: 10, x: [1, 2, 3]);

q[\y] = q[\x] * q[\n]; // similar to ~y = ~x * ~n, but in a separate name space

q.y = q.x * q.n;  // shorter way to do the same (pseudo-methods)

q.y; // [ 100, 200, 300 ]

Event for specifying different things to happen:

Event provides a defaultParentEvent that defines a variety of different event types and provides a complete set of default key/value pairs for each type. The type is determined by the value of the key \type which defaults to \note. Note events create synths on the server.

( ).play; // the default note

(freq: 500, pan: -1) .play; // 500 Hz, panned left

(play: { ~what.postln }, what: "hello happening").play; // something else

Per default, the play message derives its behaviour from the defaultParentEvent, which provides many default values, such as default instrument (\default), note (0), legato (0.8) and so on. Depending on the event type, these may differ completely and need not even represent a sound.

Class variables

defaultParentEvent the default event used in most cases

parentEvents an IdentityDictionary of useful parent events

partialEvents an IdentityDictionary of Events that define the default values and functions

for different aspects of note generation (timing, volume, pitch, server to use, etc)

Creation / Class Methods

*new(n, proto, parent, know = true)

create an event with initial size n.

proto may be provided as another event which is used to override keys in the event.

parent may be provided as another event which is used to provide default keys for the event without modifying it.

If know is set to true, the event will respond to appropriate message calls. See Environment for more details.


returns an empty event with defaultParentEvent as parent

*silent (dur)

returns an event that describes a pause of dur duration.

*addEventType(type, func)

Event types define alternate play functions that are selected by the value of ~type



play the event. This evaluates the function at \play (see example above).


Returns the inter onset time – the time delay until the next event in a sequence. This usually depends on \dur and \stretch, but may be overridden by specifying \delta directly.

Pn((dur: 2, freq:8000)).play;


Combines an event given in the argument with the current event. This is used to enable events to be composed.

(a: 6, b: 7).next((c: 100));

playAndDelta(cleanup, mute)

used by EventStreamPlayer to play Events and obtain a time increment


calls asControlInput.


Enables events to represent the server resources they created in an Event

Methods that allow Events to provide user control for Synths on Groups

synth makes the event a control interface to the resultant synth when played

group makes the event a control interface to the resultant group when played.

This is experimental, does not work consistently yet.

stop free the synth or group

pause pause the synth or group

resume resume the synth or group

release release the synth or group

set(key1, val1, ....) set a control value in the synth or group

a = (note: 2).play;

a.set(\freq, 700);


Events and SynthDefs

The key used to select what synthdef is to be played is \instrument.  In order to use a SynthDef with an Event, send it an add message. This creates a description of the SynthDef that the event can consult to determine its control names. The values of these names in the event are used when the event is played. (See SynthDesc for details.)


SynthDef(\pm, { |out=0, freq=440, amp=0.1, pan=0, gate=1, ratio = 1, index = 1, ar = 0.1, dr = 0.1|

var z;

z = LPF.ar(

PMOsc.ar(freq, freq * ratio, Linen.kr(gate, ar,index, dr), 0, 0.3),

XLine.kr(Rand(4000, 5000), Rand(2500, 3200), 1)

) * Linen.kr(gate, 0.01, 0.7, dr, 2);

OffsetOut.ar(out, Pan2.ar(z, pan, amp));



(instrument: \pm).play;

(instrument: \pm, ratio: 3.42, index: 12, freq: 150, ar: 8, dr: 3, sustain: 10).play;

note: The use of OffsetOut in the SynthDef prevents irregularities that can result from the interaction of the timing of a sequence of notes and the control rate of the Server.

Multi-channel Expansion

If a key relevant to the action is assigned an Array, the action is repeated on each element of the array:

(degree: (0..12)).play // a diatonic cluster

If several keys are assigned arrays, the action is repeated for each element of the largest array.

Smaller arrays are rotated through repeatedly.  Here are some examples:

// every other note of the diatonic cluster: stacked thirds

(degree: (0..12), amp: [0, 0.1]).play

// every other note of the semitone cluster: a wholetone cluster again

(note: (0..12), amp: [0, 0.1]).play

// every third note of the semitone cluster: a diminished chord

(note: (0..12), amp: [0, 0, 0.1]).play

// the same with different sustain times

(note: (0..12), amp: [0, 0, 0.1], sustain:[0.1, 0.3, 1.3, 2.5]).play

// timingOffset gives a tempo-relative offset time to each synth

(instrument: \pm, ratio: [2.3, 4.5, 1.7], timingOffset: [0, 1.2, 3], sustain: [0.2, 2, 1]).play;

Arrayed Arguments

It is possible to assign an array to one of a SynthDef's control names. For example:


SynthDef(\test, { | out = 0, amp = 0.01, freq = #[300,400,400], pan, gate = 1 |

var audio, env;

audio = Mix.ar(Pulse.ar(freq, 0.5)); // this is a mixture of three oscillators

env = Linen.kr(gate, susLevel: amp , doneAction: 2);  // envelope deletes the synt when done

audio = audio * env;

OffsetOut.ar(0, audio );



Within an event, arrayed arguments of this sort must be enclosed within an additional array to distinguish them from arguments intended for multi-channel expansion.

// one synth, use enclosing array to prevent multi-channel expansion

(instrument: \test, note: [[0, 2, 4]]).play

// two synths

(instrument: \test, note: [[0, 2, 4], [6, 8, 10]]).play

Events and Patterns

Events are closely integrated with the Patterns library.  Different patterns can be bound to different keys (or collections of keys) to specify the resultant music.  See the help  files Pattern and Pbind and the tutorials  Streams-Patterns-Events4 and Streams-Patterns-Events5 for more details on Patterns.

Patterns that return events may be played on a clock: dur specifies the time between two subsequent events.

// Pseq returns one item in the list after the other



(note: 2, sustain: 1, dur: 1.5), 

(note: [5, 7], sustain: 0.5, dur: 0.8), 

(note: [2, 6], sustain: 1, dur: 0.8)



// Pbind binds parameters to events:



\note, Pseq([2, [5, 7], [2, 6]]),

\sustain, Pseq([1, 0.5, 1]),

\dur, Pseq([1.5, 0.8, 0.8])



// per-event timing may be specified:



\note, Pseq([[0, 9], [5, 7], [2, 6]], inf),

\sustain, Pseq([1, 0.5, 1], inf),

\dur, Pseq([1.5, 0.8, 0.8], inf),

\timingOffset, Pseq([[0, 0.3], [0, 0.01]], inf)



Here is an example that illustrates some more of the keys defined by the defaultParentEvent.

Note that it is equivalent to write Pbind(\key, val, ...) and Pbind(*[key: val, ...]).



stepsPerOctave: Pstep(Pseq((2..12).mirror, inf),12), // 3 - 12 tone e.t. scales

note: Pseq((0..12).mirror, inf), // play full notes up and down

ctranspose: Pwhite(-0.2, 0.2), // detune up to +-20 cents

detune: Pwhite(-1.0, 1.0), // detune up to 1 Hz

sustain: Prand([0.2, 0.2, 0.2, 4], inf), // notes last 0.2 or 4 seconds

// 1 in 6 chance waits 0.8 seconds:

dur: Prand([0.2, 0.2, 0.2, 0.2, 0.2, 0.8], inf),

db: Pstep(Pseq([-15, -25, -20, -25], inf), 0.8)// 4 beat accent structure



Event's play method

When an Event  (or any other Environment) receives a use(function) message, it sets itself to be currentEnvironment, evaluates the function, and restores the original value of currentEnvironment. This allows the function to access and alter the contents of the event using the following shortcuts:

~keyName which is equivalent to currentEnvironment.at(keyName)


~keyName = value which is equivalent to currentEnvironment.put(keyName, value)

We will write ~keyName whenever referring to the value stored at the key keyName in the event.  

Here is the definition of Event's play method:

play {

if (parent.isNil) { parent = defaultParentEvent };

this.use { ~play.value };


Thus we can see that the defaultParentEvent is used unless otherwise specified and the function stored in ~play is executed in the context of the Event. It can be replaced in a given event for different behavior:

(a: 6, b: 7, play: { (~a * ~b).postln }).play;

Timing control with Event's delta method

Events also specify timing within a Pattern.  Event's delta method returns the  value of ~delta or, if that is nil,  ~dur * ~stretch. 

Patterns are played by TempoClocks, which have their own tempo controls.  This tempo which can be controlled through ~tempo in the event. Changes to the tempo affect everything else scheduled by the TempoClock, so tempo provides a global tempo control while stretch provides a control limited to the one pattern.

The structure of defaultParentEvent

The default parent event provides the collection of default values and functions needed for the different uses of an Event. These  defaults are defined in partialEvents that specify distinct aspects of default parent Event: 

playerEvent // defines ~play, ~type and ~eventTypes

serverEvent // server, group, addAction

durEvent // duration, tempo and articulation

ampEvent // volume, pan, MIDI velocity

pitchEvent // pitch specified in many different ways

bufferEvent // buffers on the server

midiEvent // defines the sending of midi messages

Useful keys for notes

Using Events is largely a matter of overwriting keys.  Here is a list of keys useful for defining notes with their default values, grouped by the partialEvent within which they are defined.

The keys in serverEvent provide the values needed to identify the server to be used and where in the tree

of nodes to place the group.  

serverEvent keys:

server: nil, // if nil, Server.default is used

instrument: \default, // this is the name of a SynthDef

group: 1, // nodeID of group on the server

// whening adding before or after a node

// this could be the nodeID of a synth instead of a group

addAction: 0, // 0, 1, 2, 3 or \addToHead, \addToTail, \addBefore, \addAfter

out: 0, // usually an output bus number, but depends on the SynthDef

The ampEvent determines volume.  Notice that ~amp is a function that determines its value from ~db. The user can choose to specify the amplitude directly by overwriting ~amp or to use a decibel specification by overwriting ~db.

ampEvent keys:

amp: #{ ~db.dbamp }, // the amplitude

db: -20.0, // the above described in decibel

pan: 0.0, // pan position: -1 left 1 right

velocity: 64 // midi velocity

trig: 0.5 // trigger value

The durEvent has keys that determine the timing of a note. Notice that ~sustain is a function that uses ~legato to determine the sustain. Like ~amp this can be overwritten to set the sustain directly.

durEvent keys:

tempo: nil, // changes tempo of a TempoClock

dur: 1.0, // time until next note (inter-onset time)

stretch: 1.0, // inverse of tempo control, specific to the Event's stream

legato: 0.8, // ratio of sustain to duration

sustain: #{ ~dur * ~legato * ~stretch },

lag: 0.0, // delay (in seconds) relative to current time position of Stream

timingOffset: 0.0, // delay (in beats) relative to current time position of Stream

strum: 0.0 // "breaks" a chord. May be negative, playing the chord backward

strumEndsTogether: false // if true, the strummed notes end together (with gated synths)

pitchEvent keys:

The pitchEvent has the most complex system of functions that provide a variety of useful ways to determine


freq (->440) // determines the pitch directly as a frequency in Hertz

midinote (-> 60) // determines pitch as a fractional MIDI note (69 -> 440)

note (-> 0) // determines pitch as a scale degree in an ~stepsPerOctave equal tempered scale

degree: 0 // determines pitch as a scale degree within the scale ~scale

The event also provides a set of transposition keys:

mtranspose: 0 // modal transposition of degree within a scale

root: 0.0 // transposes root of the scale

gtranspose: 0.0 // gamut transposition within the ~stepsPerOctave equal tempered scale

ctranspose: 0.0 // chromatic transposition within the 12 tone equal tempered scale

harmonic: 1.0 // multiplies the frequency determined by ~midinote, typically to an overtone

detune: 0.0 // directly offsets frequency by adding this value

midiToCps // a function taking a MIDI note number and turning it into frequency

// Normally this is _.midicps, but you can override it for non-ET tunings

mtranspose: 0, // modal transposition of degree

gtranspose: 0.0 // gamut transposition of note within a ~stepsPerOctave e.t. scale

ctranspose: 0.0 // chromatic transposition of midinote within 12 tone e.t. scale

octave: 5.0 // octave offest of note

root: 0.0 // root of the scale

degree: 0 // degree in scale

scale: #[0, 2, 4, 5, 7, 9, 11] // diatonic major scale

stepsPerOctave: 12.0

detune: 0.0, // detune in Hertz

harmonic: 1.0 // harmonic ratio

octaveRatio: 2.0 // size of the octave (can be used with the Scale class)

The event calculates with these keys to derive parameters needed for the synth:

note: #{ // note is the note in halftone steps from the root

(~degree + ~mtranspose).degreeToKey(~scale, ~stepsPerOctave);


midinote: #{ // midinote is the midinote (continuous intermediate values)

((~note.value + ~gtranspose + ~root) / ~stepsPerOctave + ~octave) * 12.0; 


freq: #{

(~midinote.value + ~ctranspose).midicps * ~harmonic;


detunedFreq: #{ // finally sent as "freq" to the synth as a parameter, if given

~freq.value + ~detune


Event types

An Event responds to a play message by evaluating ~play in the event, which by default uses the event's type to define the action to be performed. See Event_types.