快速傅里叶变换

/*
<script src="https://cdn.jsdelivr.net/npm/p5@2.2.0/lib/p5.js"></script>
<script src="https://cdn.jsdelivr.net/npm/p5.sound@0.2.0/dist/p5.sound.min.js"></script>
*/

function setup() {
  createCanvas(700, 400);

  fft = new p5.FFT(1024);

  mic = new p5.AudioIn();
  mic.start();
  mic.connect(fft);
}

function draw() {
  background(255);
  stroke(0);
  fill(0);

  textAlign(CENTER);
  textSize(18);
  text("快速傅里叶变换 (FFT)", width / 2, 100);

  let spectrum = fft.analyze().slice(0, 512); // 取采样值的前一半

  beginShape();
  splineVertex(0, height);
  for (i = 0; i < spectrum.length; i++) {
    let x = map(i, 0, spectrum.length, 0, width);
    let y = map(spectrum[i], 0, 0.004, height, 0);
    splineVertex(x, y);
  }
  splineVertex(width, height);
  endShape();
}