JavaScript で簡易メトロノームを作ったメモ


[JavaScript で Beep 音を鳴らす方法](http://qiita.com/isseium/items/12b215b6eab26acd2afe) では，音を鳴らす方法を書いたんですが，これを発展させてメトロノームを作ってみました．

    // tempo : テンポ（1分間に何拍するか）
    // beat  : 拍子（指定した拍数ごとに高いビープ音を鳴らす）
    function metronome(tempo, beat){
      // 低め音
      var low = "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";

      // 高めの音
      var high = "UklGRnoGAABXQVZFZm10IBAAAAABAAEAQB8AAEAfAAABAAgAZGF0YQ0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000";

      // それぞれ Audio オブジェクト生成
      var lowPlayer = new Audio("data:audio/wav;base64," + low);
      var highPlayer = new Audio("data:audio/wav;base64," + high);

      // メトロノーム設定（正確にはひとつのInterval内で処理を書いたほうがよいが簡略化のためにふたつのIntervalで設定）
      // low の再生
      setInterval(function(){
        lowPlayer.play();
      }, 60 / tempo * 1000);

      // high の再生
      setInterval(function(){
        highPlayer.play();
      }, 60 / tempo * 1000 * beat);
    }

    // メトロノームを 1分間に60拍, 4拍子でスタート    
    metronome(60, 4);

## 参考
http://www.kk.iij4u.or.jp/~kondo/wave/#data