AnalyserNode
接口的 fftSize
属性的值是一个无符号长整型的值, 表示(信号)样本的窗口大小。当执行快速傅里叶变换(Fast Fourier Transfor (FFT))时,这些(信号)样本被用来获取频域数据。
fftSize 属性的值必须是从32到32768范围内的2的非零幂; 其默认值为2048.
注意: 如果其值不是2的幂, 或者它在指定范围之外, 则抛出异常INDEX_SIZE_ERR.
语法
var audioCtx = new AudioContext();
var analyser = audioCtx.createAnalyser();
analyser.fftSize = 2048;
值
一个无符号长整型.
例子
下面的例子展示了 AudioContext
创建一个 AnalyserNode
, 然后用 requestAnimationFrame
和 <canvas>
去反复收集当前音频的时域数据, 并绘制为一个示波器风格的输出(频谱).
更多的例子/信息, 查看 Voice-change-O-matic 演示 (相关代码在 app.js 在 128行~205行).
var audioCtx = new (window.AudioContext || window.webkitAudioContext)();
var analyser = audioCtx.createAnalyser();
...
analyser.fftSize = 2048;
var bufferLength = analyser.fftSize;
var dataArray = new Uint8Array(bufferLength);
analyser.getByteTimeDomainData(dataArray);
// draw an oscilloscope of the current audio source
function draw() {
drawVisual = requestAnimationFrame(draw);
analyser.getByteTimeDomainData(dataArray);
canvasCtx.fillStyle = 'rgb(200, 200, 200)';
canvasCtx.fillRect(0, 0, WIDTH, HEIGHT);
canvasCtx.lineWidth = 2;
canvasCtx.strokeStyle = 'rgb(0, 0, 0)';
canvasCtx.beginPath();
var sliceWidth = WIDTH * 1.0 / bufferLength;
var x = 0;
for(var i = 0; i < bufferLength; i++) {
var v = dataArray[i] / 128.0;
var y = v * HEIGHT/2;
if(i === 0) {
canvasCtx.moveTo(x, y);
} else {
canvasCtx.lineTo(x, y);
}
x += sliceWidth;
}
canvasCtx.lineTo(canvas.width, canvas.height/2);
canvasCtx.stroke();
};
draw();
规范
Specification | Status | Comment |
---|---|---|
Web Audio API fftSize |
Working Draft |
浏览器兼容性
We're converting our compatibility data into a machine-readable JSON format.
This compatibility table still uses the old format,
because we haven't yet converted the data it contains.
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Feature | Chrome | Edge | Firefox (Gecko) | Internet Explorer | Opera | Safari (WebKit) |
---|---|---|---|---|---|---|
Basic support | 10.0webkit | (Yes) | 25.0 (25.0) | 未实现 | 15.0webkit 22 (unprefixed) |
6.0webkit |
Feature | Android | Edge | Firefox Mobile (Gecko) | Firefox OS | IE Mobile | Opera Mobile | Safari Mobile | Chrome for Android |
---|---|---|---|---|---|---|---|---|
Basic support | ? | (Yes) | 26.0 | 1.2 | ? | ? | ? | 33.0 |