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).
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

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung Internet
Basic supportChrome Full support 59
Notes
Full support 59
Notes
Notes Default values supported
Full support 57
Full support 10
Prefixed
Prefixed Requires the vendor prefix: webkit
Edge Full support YesFirefox Full support 25IE No support NoOpera Full support 22
Full support 22
Full support 15
Prefixed
Prefixed Requires the vendor prefix: webkit
Safari Full support 6
Prefixed
Full support 6
Prefixed
Prefixed Requires 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 Requires 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 Requires the vendor prefix: webkit
Edge Mobile Full support YesFirefox Android Full support 26Opera Android Full support YesSafari iOS No support NoSamsung Internet Android ?
Possible to disable normalisationChrome Full support YesEdge Full support YesFirefox No support NoIE No support NoOpera ? Safari ? WebView Android ? Chrome Android ? Edge Mobile Full support YesFirefox Android No support NoOpera Android ? Safari iOS ? Samsung Internet Android ?

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

Document Tags and Contributors

Last updated by: fscholz,