this is a copy from https://editor.p5js.org/p5/sketches/Sound:_FFT_Spectrum

​

 * @name Frequency Spectrum

 * @description <p>Visualize the frequency spectrum of live audio input.</p>

 * <p><em><span class="small"> To run this example locally, you will need the

 * <a href="http://p5js.org/reference/#/libraries/p5.sound">p5.sound library</a>

 * and a running <a href="https://github.com/processing/p5.js/wiki/Local-server">local server</a>.</span></em></p>

 */

let mic, fft;

let prev;

let t = 0;

let dt = 0.005;

let thestyle = 'bars'

​

function setup() {

  createCanvas(710, 400);

  background(0)

  colorMode(HSB);

  noFill();

  mic = new p5.AudioIn();

  mic.start();

  fft = new p5.FFT();

  fft.setInput(mic);

  prev = [0, height];

  selector = createSelect('hi');

  selector.option('bars');

  selector.option('lined')

  selector.input((e) => {background(0);thestyle=selector.value()})

}

​

function draw() {

  // 

​

  let spectrum = fft.analyze();

​

​

  for (i = 0; i < spectrum.length; i++) {

    stroke(noise(t)*255, 255,map(spectrum[i], 0, 255, height, 0));

​

    switch(thestyle) {

      case 'bars':

        line(i,height, i, map(spectrum[i], 0, 255, height, 0));

        break;

        case 'lined':

          line(prev[0], prev[1], i, map(spectrum[i], 0, 255, height, 0));

        default:

        break

    }

    prev = [i, map(spectrum[i], 0, 255, height, 0)]

  }

  prev = [0, height];

  t+=dt;

}

​