Audio Spectrum Analyzer - dark

A relatively simple audio spectrum analyzer built using the Web Audio API and d3.js and rendered using canvas. Also made a bright version: Audio Spectrum Analyzer - bright

This was made as part of a series exploring the visualization of audio that was presented at a d3.oakland. A big list of the demos from this series can be found here.

<!DOCTYPE html>
<html>
<title>Spectrum - Dots</title>
<style>
  body {
    margin: 0px; 
    overflow: hidden;
  }
</style>
<script src="//d3js.org/d3.v4.min.js"></script>
<canvas></canvas>
<script>
const width = innerWidth;
const height = innerHeight;

const audioCtx = new (window.AudioContext || window.webkitAudioContext)();
const analyser = audioCtx.createAnalyser();
const dataArray = new Uint8Array(analyser.fftSize/2);

const canvas = document.querySelector('canvas');
canvas.setAttribute('width',width);
canvas.setAttribute('height',height);

const canvasCtx = canvas.getContext("2d");
canvasCtx.fillStyle = 'rgb(0, 0, 0)';
canvasCtx.fillRect(0, 0, width, height);
canvasCtx.strokeStyle = 'rgb(255, 255, 255)';
canvasCtx.lineWidth = .1;

const x = d3.scaleLinear()
    .domain([0, 1024])
    .range([50, width - 55]);

const y = d3.scaleLinear()
    .domain([0, 255])
    .range([height - 55, 50]);

const colors = d3.scaleLinear()
    .domain([0, 100])
    .range(['black', 'red']);

navigator.getUserMedia (
  {audio: true},
  function(stream) {
    audioCtx.createMediaStreamSource(stream).connect(analyser);
    draw();
  },
  function(err) {
    console.log('The following gUM error occured: ' + err);
  }
);

function draw() {
  analyser.getByteFrequencyData(dataArray)
  canvasCtx.fillStyle = 'rgba(0, 0, 0, .2)';
  canvasCtx.fillRect(0, 0, width, height);
  for (let i in dataArray) {
    canvasCtx.beginPath();
    canvasCtx.fillStyle = colors(dataArray[i]);
    canvasCtx.arc(x(i), y(dataArray[i]), 2, 0, 2*Math.PI);
    canvasCtx.fill();
    canvasCtx.stroke();
  }
  requestAnimationFrame(draw);
}
</script>
</html>

https://d3js.org/d3.v4.min.js