Slow Down SML Music (using counter)
Basis: Instead of playing once, it does nothing once in it's place, half of the time. This halves the speed of music.

0457 = Dec an address example

FE 01 CP A, 01

Address = DFFF

Write to ROM Address 7FD9:
F5 (Push AF)
FA (Load 2 Byte Address DFFF)
FF
DF
3D (Dec A)
EA (Store 2 Byte Address DFFF)
FF
DF
FE 00 (Compare A with 00)
28 07 (If equal, jump 7 bytes, which plays the music)
3E 01 (load A with 1)
EA (Store A to 2 Byte Address DFFF)
FF
DF
F1 (Pop AF)
C9 (Ret)
F1 (Pop AF...needed because it won't get popped if you Ret instead of JR)
C36266

Change 7FF0 to jump to 7FD9, since that's a music-run referencial jump.


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The following is some info that applies to the changes I made to level 3 objects.

Breakpoint 21FF in BGB, with the VRAM Viewer on. That'll tell you the general area to look for that level's data. I can look it up easily enough by putting a read watch on the data. That's about the extent of what I did, in the way of hard parts.