BaseAudioContext.createPeriodicWave()

The createPeriodicWave() method of the BaseAudioContext Interface is used to create a PeriodicWave, which is used to define a periodic waveform that can be used to shape the output of an OscillatorNode.

Syntax

var wave = AudioContext.createPeriodicWave(real, imag[, constraints]);

Returns

A PeriodicWave.

Parameters

real
An array of cosine terms (traditionally the A terms).
imag
An array of sine terms (traditionally the B terms).

The real and imag arrays have to have the same length, otherwise an error is thrown.

constraints Optional
An dictionary object that specifies whether normalization should be disabled (if not specified, normalization is enabled by default.) It takes one property:
  • disableNormalization: If set to true, normalization is disabled for the periodic wave. The default is false.

If normalized, the resulting wave will have a maximum absolute peak value of 1.

Example

The following example illustrates simple usage of createPeriodicWave(), to create a PeriodicWave object containing a simple sine wave.

var real = new Float32Array(2);
var imag = new Float32Array(2);
var ac = new AudioContext();
var osc = ac.createOscillator();

real[0] = 0;
imag[0] = 0;
real[1] = 1;
imag[1] = 0;

var wave = ac.createPeriodicWave(real, imag, {disableNormalization: true});

osc.setPeriodicWave(wave);

osc.connect(ac.destination);

osc.start();
osc.stop(2);

This works because a sound that contains only a fundamental tone is by definition a sine wave

Here, we create a PeriodicWave with two values. The first value is the DC offset, which is the value at which the oscillator starts. 0 is good here, because we want to start the curve at the middle of the [-1.0; 1.0] range.

The second and subsequent values are sine and cosine components. You can think of it as the result of a Fourier transform, where you get frequency domain values from time domain value. Here, with createPeriodicWave(), you specify the frequencies, and the browser performs an inverse Fourier transform to get a time domain buffer for the frequency of the oscillator. Here, we only set one component at full volume (1.0) on the fundamental tone, so we get a sine wave.

The coefficients of the Fourier transform should be given in ascending order (i.e. (a+bi)ei,(c+di)e2i,(f+gi)e3i\left(a+bi\right)e^{i} , \left(c+di\right)e^{2i} , \left(f+gi\right)e^{3i} etc.) and can be positive or negative. A simple way of manually obtaining such coefficients (though not the best) is to use a graphing calculator.

Specifications

Specification Status Comment
Web Audio API
The definition of 'createPeriodicWave' in that specification.
Working Draft

Browser compatibility

DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
createPeriodicWaveChrome Full support 59
Notes
Full support 59
Notes
Notes Default values supported
Full support 57
Full support 10
Prefixed
Prefixed Implemented with the vendor prefix: webkit
Edge Full support ≤18Firefox Full support 53
Notes
Full support 53
Notes
Notes Originally implemented on AudioContext in Firefox 25.
IE No support NoOpera Full support 22
Full support 22
Full support 15
Prefixed
Prefixed Implemented with the vendor prefix: webkit
Safari Full support 6
Prefixed
Full support 6
Prefixed
Prefixed Implemented with the vendor prefix: webkit
WebView Android Full support 59
Notes
Full support 59
Notes
Notes Default values supported
Full support 57
Full support 4.4.3
Prefixed
Prefixed Implemented with the vendor prefix: webkit
Chrome Android Full support 59
Notes
Full support 59
Notes
Notes Default values supported
Full support 57
Full support 33
Prefixed
Prefixed Implemented with the vendor prefix: webkit
Firefox Android Full support 53
Notes
Full support 53
Notes
Notes Originally implemented on AudioContext in Firefox Android 26.
Opera Android Full support 22
Full support 22
Full support 14
Prefixed
Prefixed Implemented with the vendor prefix: webkit
Safari iOS Full support 6
Prefixed
Full support 6
Prefixed
Prefixed Implemented with the vendor prefix: webkit
Samsung Internet Android Full support 7.0
Notes
Full support 7.0
Notes
Notes Default values supported
Full support 7.0
Full support 2.0
Prefixed
Prefixed Implemented with the vendor prefix: webkit
Possible to disable normalisationChrome Full support YesEdge Full support ≤18Firefox No support NoIE No support NoOpera ? Safari No support NoWebView Android Full support YesChrome Android Full support YesFirefox Android No support NoOpera Android ? Safari iOS No support NoSamsung Internet Android Full support Yes

Legend

Full support
Full support
No support
No support
Compatibility unknown
Compatibility unknown
See implementation notes.
See implementation notes.
Requires a vendor prefix or different name for use.
Requires a vendor prefix or different name for use.

See also