I have noticed that in PartialMT32.h the USE_MMX directive has been
set to 1 therefore enabling some of the MMX routines in CPartialMT32.cpp and disabling others (depending on whether the comparason is '== 0' or '!= 2'). From this I assume that some of the MMX routines are not up to date and in those cases the C language routines should be used instead.

I have found that the C code version and the MMX code version for mixBuffersRing give different results on my setup (the C code version is very soft for some reason). Can I always assume that the C code version is correct when testing or should I just use the defaults?

Various values for USE_MMX enable various extentions, e.g. MMX., SIMD IIRC.
V.

Yeah, except that the == 2 stuff is a crude way to disable the code from being run at all. That defined out code doesn't work right now.

i experiment the same problems if i use the mt-32 windows driver in my midi sequencer.
No sound at all!.
and when i try to listen a midi mt-32 comatible file, all sounds rong.
What can i do?

Very neat CC, I was able to obtain the MT32 PCM Rom just recently and tried it out on your latest build. Ultima Underworld 1 seems to work great with it. Except when I exited I was assaulted by a horrific beeping noise. Gah... 🤣. But it was actually really cool to hear another soundcard which I never officially heard before. Only Soundcards I know by heart are the Soundblasters.
BTW UW1 utilizes using Roland MT-32 -Music and SB -digitzed sfx.

Seems to affect both UW1 and 2.