The number in each song title is its speed in beats per minute.
This album is meant as background for an 8-bit game such as Breakout or Tetris. On each beat, the active block drops a space. Each time a level is cleared, the game goes to the next song and increases in speed. The soundtrack starts off simple and slow at 120BPM; by 160BPM it's lively and steady, and at 220BPM it's all but a craze of notes. When the last song is cleared, the entire soundtrack loops and the blocks fall twice per beat.
Created in Garage Band with the Magical 8-Bit Plug plugin.