Skeetendo

I am attempting to figure out how to compose music in Pokecrystal disassembly, and am confused about the musicheader macro used for the music files. The code description lists the arguments as "n, index, and address". Address is self explanatory, and I can assume index is for the channel (1-4) used for that code, but I am unclear on what the n argument is. I wasn't able to determine an obvious pattern based on the existing files.