> Amiga MOD uses CIA I/O chip for reference.
bro, i didn't know amigas were made by the us government '-'
jokes aside, that makes much more sense now. from what i understood, the samples were loaded faster in dos by default, so they had higher pitch. i think i've heard of the same problem in the apple iigs. the iigs uses an ensoniq es5503 doc as the sound chip, but it's not sample-based, instead, it's wavetable. so i think the "hack" they used had a disadvantage of playing samples in a faster speed, making them higher pitch. and according to wikipedia, the timer for the iigs sound is in the sound chip itself, but it uses a whole channel for that timing if the program that's running relies on the system firmware or stock tools. if it doesn't, then it's fully possible to use all 32 channels, though i've never seen any iigs music use all these channels, nor have i seen a demo or tracker that can break this limitation. so i'm guessing the default timing on the iigs sound chip was much different, but programmers didn't bother with fixing that to make music sound the same as in the amiga.
> DOS players have to emulate that based on code trying to divide time over a period linked to the VSYNC (I think, its something like that, im not 100%)
i think openmpt does the same thing. amiga music also sounds higher-pitched there. maybe they didn't separate the code that much for amiga and dos, see, if you play an amiga module in protracker 2 clone for windows/ linux/ whatever, it will sound the exact same thing as in a real amiga. the code in there has a much better emulation i assume. though, there are some flaws that can be fixed.
