BaseAudioContext.createPeriodicWave()

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createPeriodicWave() 方法在 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 .

句法

var wave = AudioContext.createPeriodicWave(real, imag[, constraints]);

A PeriodicWave .

参数

real
imag

real and imag arrays have to have the same length, otherwise an error is thrown.

constraints 可选

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.

范例

The following example illustrates simple usage of createPeriodicWave() ，要创建 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. $\left(a+bi\right)e^{i} , \left(c+di\right)e^{2i} , \left(f+gi\right)e^{3i}$ 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.

规范

规范	状态	注释
Web 音频 API The definition of 'createPeriodicWave' in that specification.	工作草案

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	桌面						移动
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`createPeriodicWave`	Chrome 59 注意事项 59 注意事项 Default values supported 57 10 Prefixed Prefixed Implemented with the vendor prefix: webkit	Edge ≤18	Firefox 53 注意事项 53 注意事项 Originally implemented on `AudioContext` in Firefox 25.	IE 不支持 No	Opera 22 22 15 Prefixed Prefixed Implemented with the vendor prefix: webkit	Safari 6 Prefixed 6 Prefixed Prefixed Implemented with the vendor prefix: webkit	WebView Android 59 注意事项 59 注意事项 Default values supported 57 4.4.3 Prefixed Prefixed Implemented with the vendor prefix: webkit	Chrome Android 59 注意事项 59 注意事项 Default values supported 57 33 Prefixed Prefixed Implemented with the vendor prefix: webkit	Firefox Android 53 注意事项 53 注意事项 Originally implemented on `AudioContext` in Firefox Android 26.	Opera Android 22 22 14 Prefixed Prefixed Implemented with the vendor prefix: webkit	Safari iOS 6 Prefixed 6 Prefixed Prefixed Implemented with the vendor prefix: webkit	Samsung Internet Android 7.0 注意事项 7.0 注意事项 Default values supported 7.0 2.0 Prefixed Prefixed Implemented with the vendor prefix: webkit
Possible to disable normalisation	Chrome Yes	Edge ≤18	Firefox 不支持 No	IE 不支持 No	Opera ?	Safari 不支持 No	WebView Android Yes	Chrome Android Yes	Firefox Android 不支持 No	Opera Android ?	Safari iOS 不支持 No	Samsung Internet Android Yes

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最后修改： Mar 28, 2020

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