Mac Boot Beep translated to JavaScript

gistfile1.js

/**
 * Adapted from http://folklore.org/projects/Macintosh/more/BootBeep.txt
 * A direct translation of the m68k asm into JavaScript.
 * @returns {Buffer} a Buffer which  corresponds to the audio buffer on the
 * original Macintosh, repeated for the duration of the boot beep. The Buffer
 * contains a series of words, where the lower byte of each word is the
 * amplitude of the audio signal at this point.
 */
var bootbeepASM = function() {
  d3 = 40;  // D3 contains the duration: 40 is boot beep

  var output = new Buffer(0);
  var buffer = new Buffer(2 * 5 * 4 * 19);

  var a0 = 0;  // get sound buffer address
  var a1 = 0;

  console.log("Initializing buffer.");

  // repeat 74 byte sequence 5 times
  _.times(5, function() {
    // 4 byte table to fill buffer with
    _.each([0x06, 0xC0, 0x40, 0xFA], function(d1) {
      _.times(19, function() {         // repeat 19 times
        buffer.writeUInt16LE(d1, a0);  // move in a byte
        a0 += 2;                       // bump to next buffer location
      });
    });
  });

  console.log("Filtering buffer " + d3 + " times.");

  // OK, now filter it for a nice fade -- repeat the filtering process D3 times
  _.times(d3, function() {
    a0 = 0;         // point A0 to start of buffer
    a1 = a0 + 146;  // point A1 74 values in
    // process 74 samples
    _.times(74, function() {
      var d2 = buffer.readUInt8(a1);  // get 74th value
      a1 += 4;                        // bump to 76th value
      var d1 = buffer.readUInt8(a1);  // make it a word value (lol, no)
      d2 += d1;                       // add to the accumulator
      a1 -= 2;                        // point at 75th value
      d1 = buffer.readUInt8(a1);      // get it
      d2 += d1;                       // add to the accumulator
      d2 += d1;                       // count it twice

      d2 = Math.round(d2 / 4);        // divide it by 4
      buffer.writeUInt8(d2, a0);      // store it away
      a0 += 2;                        // bump to next value
    });

    // 296 values to copy
    _.times(296, function() {
      buffer.writeUInt8(buffer.readUInt8(a0 - 74), a0);
      a0 += 2;
    });

    // Only the first 370 words is actually used by the Mac audio buffer.
    output = Buffer.concat([output, buffer.slice(0, 2 * 370)]);
  });

  return output;
};