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 totrue
, normalization is disabled for the periodic wave. The default isfalse
.
-
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, {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. 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 |
---|
Web Audio API # dom-baseaudiocontext-createperiodicwave |
Browser compatibility
BCD tables only load in the browser