音声をなみなみさせる

マイクで入力した音声をフーリエ変換してcanvasに表示するデモです。
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>音声なみなみ</title>
</head>
<body>
  <body>
    <main>
      <h1>音声をなみなみで表示します！</h1>
      <canvas></canvas>
      <button id="btn">音声！</button>
    </main>
    <script type="module">
      document.querySelector('#btn').addEventListener('click', async () => {
        // マイクアクセス
        const stream = await navigator.mediaDevices.getUserMedia({ audio: true, video: false })

        const context = new AudioContext()
        // 音源を作成
        const mediaStream = context.createMediaStreamSource(stream);

        const analyzer = context.createAnalyser();
        // 音源　→　解析機　→　出力
        mediaStream.connect(analyzer);
        analyzer.connect(context.destination);

        analyzer.fftSize = 2048;

        const canvas = document.querySelector('canvas');
        const canvasContext = canvas.getContext('2d');
        canvasContext.strokeStyle = "blue"

        window.setInterval(() => {
            const times = new Uint8Array(analyzer.fftSize);
            analyzer.getByteTimeDomainData(times);
            canvasContext.clearRect(0, 0, canvas.width, canvas.height);
            canvasContext.beginPath();

            for (let i = 0, len = times.length; i < len; i++) {
              const x = (i / len) * canvas.width; // 正規化
              const y = (1 - (times[i] / 255)) * canvas.height; // 正規化

              if (i === 0) {
                canvasContext.moveTo(x, y);
              } else {
                canvasContext.lineTo(x, y);
              }
            }
            canvasContext.stroke();
        }, 300);
      })
    </script>
  </body>
</body>
</html>