AudioContext.createPeriodicWave()
The createPeriodicWave()
method of the AudioContext
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 audioCtx = new AudioContext(); var wave = audioCtx.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 totrue
, normalization is disabled for the periodic wave.
Note: 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,<code> {disableNormalization: true}</code>); 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 a 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. 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
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari (WebKit) |
---|---|---|---|---|---|
Basic support | 10.0webkit | 25.0 (25.0) | No support | 15.0webkit 22 (unprefixed) |
6.0webkit |
Disable normalisation | yes | no | ? | ? | ? |
Feature | Android | Android Webview | Firefox Mobile (Gecko) | Firefox OS | IE Mobile | Opera Mobile | Safari Mobile | Chrome for Android |
---|---|---|---|---|---|---|---|---|
Basic support | ? | (Yes) | 26.0 | 1.2 | ? | ? | ? | 33.0 |
Disable normalisation | ? | ? | no | no | ? | ? | ? | ? |
See also
License
© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-us/docs/web/api/audiocontext/createperiodicwave