AnalyserNode.frequencyBinCount

frequencyBinCount 的值固定为 AnalyserNode 接口中 fftSize 值的一半。该属性通常用于可视化的数据值的数量。

语法

var audioCtx = new AudioContext();
var analyser = audioCtx.createAnalyser();
var bufferLength = analyser.frequencyBinCount;

值类型

无符号长整形 (unsigned long).

例子

下面的例子展示了 AudioContext 创建一个 AnalyserNode, 然后用 requestAnimationFrame 和 <canvas> 去反复收集频率数据,并绘制为一个柱状风格的输出 (频谱).

更多的例子/信息,查看 Voice-change-O-matic 演示 (相关代码在 app.js 的 128 行~205 行).

var audioCtx = new (window.AudioContext || window.webkitAudioContext)();
var analyser = audioCtx.createAnalyser();
analyser.minDecibels = -90;
analyser.maxDecibels = -10;

  ...

analyser.fftSize = 256;
var bufferLength = analyser.frequencyBinCount;
console.log(bufferLength);
var dataArray = new Uint8Array(bufferLength);

canvasCtx.clearRect(0, 0, WIDTH, HEIGHT);

function draw() {
  drawVisual = requestAnimationFrame(draw);

  analyser.getByteFrequencyData(dataArray);

  canvasCtx.fillStyle = 'rgb(0, 0, 0)';
  canvasCtx.fillRect(0, 0, WIDTH, HEIGHT);

  var barWidth = (WIDTH / bufferLength) * 2.5;
  var barHeight;
  var x = 0;

  for(var i = 0; i < bufferLength; i++) {
    barHeight = dataArray[i];

    canvasCtx.fillStyle = 'rgb(' + (barHeight+100) + ',50,50)';
    canvasCtx.fillRect(x,HEIGHT-barHeight/2,barWidth,barHeight/2);

    x += barWidth + 1;
  }
};

draw();

规范

Specification
Web Audio API
# dom-analysernode-frequencybincount

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