snippet.js

    var FFT = function(_bufferSize) {
      var bufferSize = _bufferSize;

      var self = {
        // constructor
        initialize: function(){
          self.reverseTable = self.buildReverseTable();
          return self;
        },

        // Build a table of FFT values
        buildReverseTable: function() {
          var reverseTable = new Array(bufferSize);
          reverseTable[0] = 0;

          var limit = 1;
          var bit = bufferSize >> 1;

          while ( limit < bufferSize ) {
            for ( var i = 0; i < limit; i++ ) {
              reverseTable[i + limit] = reverseTable[i] + bit;
            }

            limit = limit << 1;
            bit = bit >> 1;
          }
          return reverseTable;
        }
      };

      return self.initialize();
    }