Revision 693185 of AudioContext.createPeriodicWave()

<p>{{ APIRef("AudioContext") }}</p>
<div>
 <p>The <code>createPeriodicWave()</code> method of the {{ domxref("AudioContext") }} Interface is used to create a {{domxref("PeriodicWave")}}, which is used to define a periodic waveform that can be used to shape the output of an {{ domxref("OscillatorNode") }}.</p>
</div>
<h2 id="Syntax">Syntax</h2>
<pre class="brush: js">
var audioCtx = new AudioContext();
var wave = audioCtx.createPeriodicWave(real, imag);</pre>
<h3 id="Returns">Returns</h3>
<p>A {{domxref("PeriodicWave")}}.</p>
<h2 id="Example">Example</h2>
<p>The following example illustrates simple usage of <code>createPeriodicWave()</code>, to create a {{domxref("PeriodicWave")}} object containing a simple sine wave.</p>
<pre class="brush: js;highlight[11]">
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);

osc.setPeriodicWave(wave);

osc.connect(ac.destination);

osc.start();
osc.stop(2);</pre>
<p>This works because a sound that contains only a fundamental tone is by definition a sine wave.<br />
 <br />
 Here, we create a <code>PeriodicWave</code> 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.</p>
<p>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 <code>createPeriodicWave()</code>, 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.</p>
<p>The coefficients of the Fourier transform should be given in <em>ascending</em> order (i.e.&nbsp;<math xmlns="https://www.w3.org/1998/Math/MathML"><semantics><mrow><mrow><mo>(</mo><mrow><mi>a</mi><mo>+</mo><mi>b</mi><mi>i</mi></mrow><mo>)</mo></mrow><msup><mi>e</mi><mi>i</mi></msup><mo>,</mo><mrow><mo>(</mo><mrow><mi>c</mi><mo>+</mo><mi>d</mi><mi>i</mi></mrow><mo>)</mo></mrow><msup><mi>e</mi><mrow><mn>2</mn><mi>i</mi></mrow></msup><mo>,</mo><mrow><mo>(</mo><mrow><mi>f</mi><mo>+</mo><mi>g</mi><mi>i</mi></mrow><mo>)</mo></mrow><msup><mi>e</mi><mrow><mn>3</mn><mi>i</mi></mrow></msup></mrow><annotation encoding="TeX">\left(a+bi\right)e^{i} , \left(c+di\right)e^{2i} , \left(f+gi\right)e^{3i} &nbsp;&nbsp;</annotation></semantics></math>etc.) and can be positive or negative. &nbsp;A simple way of manually obtaining such coefficients (though not the best) is to use a graphing calculator.</p>
<h2 id="Parameters">Parameters</h2>
<p>None.</p>
<h2 id="Specifications">Specifications</h2>
<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">Specification</th>
   <th scope="col">Status</th>
   <th scope="col">Comment</th>
  </tr>
  <tr>
   <td>{{SpecName('Web Audio API', '#widl-AudioContext-createPeriodicWave-PeriodicWave-Float32Array-real-Float32Array-imag', 'createPeriodicWave')}}</td>
   <td>{{Spec2('Web Audio API')}}</td>
   <td>&nbsp;</td>
  </tr>
 </tbody>
</table>
<h2 id="Browser_compatibility">Browser compatibility</h2>
<div>
 {{CompatibilityTable}}</div>
<div id="compat-desktop">
 <table class="compat-table">
  <tbody>
   <tr>
    <th>Feature</th>
    <th>Chrome</th>
    <th>Firefox (Gecko)</th>
    <th>Internet Explorer</th>
    <th>Opera</th>
    <th>Safari (WebKit)</th>
   </tr>
   <tr>
    <td>Basic support</td>
    <td>{{CompatChrome(10.0)}}{{property_prefix("webkit")}}</td>
    <td>{{CompatGeckoDesktop(25.0)}}&nbsp;</td>
    <td>{{CompatNo}}</td>
    <td>15.0{{property_prefix("webkit")}}<br />
     22 (unprefixed)</td>
    <td>6.0{{property_prefix("webkit")}}</td>
   </tr>
  </tbody>
 </table>
</div>
<div id="compat-mobile">
 <table class="compat-table">
  <tbody>
   <tr>
    <th>Feature</th>
    <th>Android</th>
    <th>Firefox Mobile (Gecko)</th>
    <th>Firefox OS</th>
    <th>IE Mobile</th>
    <th>Opera Mobile</th>
    <th>Safari Mobile</th>
    <th>Chrome for Android</th>
   </tr>
   <tr>
    <td>Basic support</td>
    <td>{{CompatUnknown}}</td>
    <td>26.0</td>
    <td>1.2</td>
    <td>{{CompatUnknown}}</td>
    <td>{{CompatUnknown}}</td>
    <td>{{CompatUnknown}}</td>
    <td>33.0</td>
   </tr>
  </tbody>
 </table>
</div>
<h2 id="See_also">See also</h2>
<ul>
 <li><a href="/en-US/docs/Web_Audio_API/Using_Web_Audio_API">Using the Web Audio API</a></li>
</ul>