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AudioContext.createPeriodicWave()

この翻訳は不完全です。英語から この記事を翻訳 してください。

AudioContextインターフェースのcreatePeriodicWave()メソッドは、周期的な波形を定義するために使われるPeriodicWaveを生成します。これはOscillatorNodeの出力を決めるために使われます。

構文

var audioCtx = new AudioContext();
var wave = audioCtx.createPeriodicWave(real, imag);

戻り値

PeriodicWave

引数

real
余弦項の配列 (伝統的なA項)
imag
正弦項の配列 (伝統的なB項)

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);

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. (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.

仕様

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

ブラウザ互換性

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 10.0webkit 25.0 (25.0)  未サポート 15.0webkit
22 (unprefixed)
6.0webkit
Feature Android Android Webview Firefox Mobile (Gecko) Firefox OS IE Mobile Opera Mobile Safari Mobile Chrome for Android
Basic support ? (有) 26.0 1.2 ? ? ? 33.0

参考

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 このページの貢献者: maruhiro
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