Because apparently this is something that's come up a lot lately.
SO LISTEN UP ALL YOU BAMBLERS, I'M GONNA SHOW YOU HOW TO LOOP SOME TUNES. IT'S REAL EASY ALL YOU NEED IS AUDACITY
For the sake of example, I'm just gonna reloop Mega Man 7 Wily Boss. Since that's an easy loop.
SO HERE'S AUDACITY
this picture is fucking huge and i'm tired so i might resize it later, don't worry about it.
So you got your song, now there's one important thing at the very bottom

Boom, all of these things are set to samples. It is possible to do this with other settings BUT I NEVER HAVE SO WE DOIN' SAMPLES
So we got our song here and our goal is to make the file as small as we can while you know, still having the song. With looping we can cut it down real easily. So step 1 is to just cut the song off where it loops, so the file plays one time through exactly.

So the song repeats right here.

Delete that shit.
The next step is to find the exact moment of the song where the loop begins. This means that if the song has an intro that doesn't loop, to just find the exact moment where the actual loop does begin. In this case, it's right here.

Everything to the left of that line is the intro, everything to the right is what is being looped.
Now you can select the entire song after the loop and hold shift+play to listen to the song repeat that selection to make sure your loop is ACCURATE but you don't need any pics for that.
Once you're sure everything is in the right place, take note of the sample number at the very bottom.

For this, selection start is the only part that matters. That number is important and is the key to looping this shit.
So hey we got everything you want to open file and hit Export Audio
You generally want to export the file as an OGG because it's the file 8BDM uses for its tunes.
Once you give it a name, this box should appear

Depending on the file, there might be other info but it doesn't matter. What you want to do is on the first blank line, on the left column you want to add "LOOP_START" and on the right column, you want to copy over the sample number seen on Selection Start. However, it's very important you don't include any commas or anything.
So in the case of this song, the Metadata would look like this.

And baboom, hit okay, upload that ogg to the wad of your choice and if you did everything right, you now have a looping song.
it's a christmas miracle