こちらをzipで落としてきて使いました。
mdn/voice-change-o-matic

##完成品
始めるを押すと、canvasの中にバーを表示する

##ソースコード
html

<!DOCTYPE html>
<html lang="en-us">
<head>
	<meta charset="utf-8">	
</head>
<body>
	<div class="wrapper">
		<div style="width:200px;overflow: hidden;">
	    	<canvas class="visualizer" width="200" height="100"></canvas> 
	    <div>

		<a id="startWave">始める</a>
	</div>
    <script src="scripts/sound-bar.js"></script>
</body>
</html>

js

let start = document.getElementById('startWave');
start.onclick = startWaveAnimation;

function startWaveAnimation() {
  // Older browsers might not implement mediaDevices at all, so we set an empty object first
  if (navigator.mediaDevices === undefined) {
    navigator.mediaDevices = {};
  }

  // Some browsers partially implement mediaDevices. We can't just assign an object
  // with getUserMedia as it would overwrite existing properties.
  // Here, we will just add the getUserMedia property if it's missing.
  if (navigator.mediaDevices.getUserMedia === undefined) {
    navigator.mediaDevices.getUserMedia = function(constraints) {

      // First get ahold of the legacy getUserMedia, if present
      var getUserMedia = navigator.webkitGetUserMedia || navigator.mozGetUserMedia || navigator.msGetUserMedia;

      // Some browsers just don't implement it - return a rejected promise with an error
      // to keep a consistent interface
      if (!getUserMedia) {
        return Promise.reject(new Error('getUserMedia is not implemented in this browser'));
      }

      // Otherwise, wrap the call to the old navigator.getUserMedia with a Promise
      return new Promise(function(resolve, reject) {
        getUserMedia.call(navigator, constraints, resolve, reject);
      });
    }
  }

  // set up forked web audio context, for multiple browsers
  // window. is needed otherwise Safari explodes

  var audioCtx = new (window.AudioContext || window.webkitAudioContext)();
  var source;
  var stream;

  // grab the mute button to use below

  var mute = document.querySelector('.mute');

  //set up the different audio nodes we will use for the app

  var analyser = audioCtx.createAnalyser();
  analyser.minDecibels = -90;
  analyser.maxDecibels = -10;
  analyser.smoothingTimeConstant = 0.85;

  var distortion = audioCtx.createWaveShaper();
  var gainNode = audioCtx.createGain();
  var biquadFilter = audioCtx.createBiquadFilter();
  var convolver = audioCtx.createConvolver();

  function makeDistortionCurve(amount) {
    var k = typeof amount === 'number' ? amount : 50,
      n_samples = 44100,
      curve = new Float32Array(n_samples),
      deg = Math.PI / 180,
      i = 0,
      x;
    for ( ; i < n_samples; ++i ) {
      x = i * 2 / n_samples - 1;
      curve[i] = ( 3 + k ) * x * 20 * deg / ( Math.PI + k * Math.abs(x) );
    }
    return curve;
  };

  // set up canvas context for visualizer

  var canvas = document.querySelector('.visualizer');
  var canvasCtx = canvas.getContext("2d");

  var intendedWidth = document.querySelector('.wrapper').clientWidth;

  canvas.setAttribute('width',intendedWidth);

  var visualSelect = document.getElementById("visual");

  var drawVisual;

  //main block for doing the audio recording

  if (navigator.mediaDevices.getUserMedia) {
     console.log('getUserMedia supported.');
     var constraints = {audio: true}
     navigator.mediaDevices.getUserMedia (constraints)
        .then(
          function(stream) {
             source = audioCtx.createMediaStreamSource(stream);
             source.connect(distortion);
             distortion.connect(biquadFilter);
             biquadFilter.connect(gainNode);
             convolver.connect(gainNode);
             gainNode.connect(analyser);
             analyser.connect(audioCtx.destination);

          	 visualize();
             voiceChange();
        })
        .catch( function(err) { console.log('The following gUM error occured: ' + err);})
  } else {
     console.log('getUserMedia not supported on your browser!');
  }

  function visualize() {
    WIDTH = canvas.width;
    HEIGHT = canvas.height;


      analyser.fftSize = 256;
      var bufferLengthAlt = analyser.frequencyBinCount;
      console.log(bufferLengthAlt);
      var dataArrayAlt = new Uint8Array(bufferLengthAlt);

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

      var drawAlt = function() {
        drawVisual = requestAnimationFrame(drawAlt);

        analyser.getByteFrequencyData(dataArrayAlt);

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

        var barWidth = 20; //一本一本のバー横幅はここでpx指定
        var barHeight;
        var x = 0;

        for(var i = 0; i < bufferLengthAlt; i++) {
          barHeight = barColor = dataArrayAlt[i];
          canvasCtx.fillStyle = barColer(barHeight);
          canvasCtx.fillRect(x,HEIGHT-barHeight/2,barWidth,barHeight/2);

          x += barWidth + 1;
        }
      };

      drawAlt();
  }

  function barColer(barHeight){ //ピンク色にしてねっていう依頼があったため
    var barColor = 'rgb(255, ' + (200 - barHeight) + '  ,177)';
    if(barHeight > 200 || (200 - barHeight) < 0){
       barColor = 'rgb(255,157,207)';
    }
    return barColor
  }


  function voiceChange() {

    distortion.oversample = '4x';
    biquadFilter.gain.setTargetAtTime(0, audioCtx.currentTime, 0)

    var voiceSetting = voiceSelect.value;
    console.log(voiceSetting);

    //when convolver is selected it is connected back into the audio path
    if(voiceSetting == "convolver") {
      biquadFilter.disconnect(0);
      biquadFilter.connect(convolver);
    } else {
      biquadFilter.disconnect(0);
      biquadFilter.connect(gainNode);

      if(voiceSetting == "distortion") {
        distortion.curve = makeDistortionCurve(400);
      } else if(voiceSetting == "biquad") {
        biquadFilter.type = "lowshelf";
        biquadFilter.frequency.setTargetAtTime(1000, audioCtx.currentTime, 0)
        biquadFilter.gain.setTargetAtTime(25, audioCtx.currentTime, 0)
      } else if(voiceSetting == "off") {
        console.log("Voice settings turned off");
      }
    }
  }

}

canvasのサイズがDeviceのwidthとなっているので、とりあえずdivで無理やり制御。
いらない記述が残っているかもしれませんが、まだそこまでじっくり見ていません。
console.logとかは消してもいいだろうなー
エラーの出し方はもっと工夫するべき。

名前空間作ろうね。