Minecraft wiki entry for Redstone_music, associated text: Rhythm is another important factor of music, which is basically how long a note is held for. The next table shows how many redstone ticks, using repeaters, must go after a note block, depending on the tempo of the music, and what kind of rhythm the note is. Remember; the maximum number of ticks for one repeater is 4, so if you need more than 4 ticks, you need more than one repeater. Also, the numbers you see on top is the tempo of the music, which is how many beats there are in a minute.