What the wiki says is basically this:
First you need your complete track, then think about how many times will you split that track... let's say... 20 times (the more you split it, the faster the track will "Switch" from Ambience to Battle music and so on).
Now 20 will be you NM (number of mesures), with this you already have one part of your formula "SPM = 2 * SF * L / NM" complete.
Now SF is a constant (sampling frequency) on every track, so you just cross that off the list.
now you are missing the variable "L" which is the lenght of the music track in seconds OF EVERY PIECE, so... basically what you need to do here is:
Take the original file, write down the exact lenght in seconds (if you got a minute, replace it with 60 secs ^^) then take your "NM" variable and divide the total seconds by NM, this will be your "L" variable.
That's it.
a note aside, when you are gonna use a custom made music table, in your mission editor place only the your custom music pack, never use the "use this music pack if not present" because it seems to override the custom made music pack even if it works correctly.
