The way the condition for checking if an instrument is valid, it should
be valid if the music player and MIDI driver agree on whether it's MT-32
MIDI. Otherwise, it's only valid if the instrument can be mapped to or
from MT-32.
But the way the check was written, it would always look for an
instrument mapping, since || binds harder than the ? operator.
All MT-32 instruments can be mapped to General MIDI, but a few General
MIDI instrument can't be mapped to MT-32. So theoretically, this should
have happened a lot. However, the GM instruments that can't be mapped
are mostly sound effects. The only cases where I've actually heard it
is with the Mac versions of Monkey Island 2 and Fate of Atlantis. They
provide their own digitized instruments, so who knows how those numbers
were assigned.
Two obvious early cases were the swamp music in Monkey Island 2 and the
New York music in Fate of Atlantis. Both were missing a "wood block"
instrument, among other things.
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