Comment by boomlinde

There's a "correct" sound in that the MIDI standard itself doesn't specify a standard instrument assignment. For that, there's General MIDI but also entirely different approaches (like the MT-32 instrument assignment, which predates General MIDI) and extensions to General MIDI (like Roland's GS and Yamaha's XG). Some didn't have a standard assignment at all (like the FB-01). Even the Adlib and earlier Soundblaster cards didn't have exactly GM compatible MIDI playback drivers; General MIDI specifies a minimum number of 24 simultaneous voices, and an OPL2 or even a pair of them can't satisfy that requirement.

There's also a "correct" sound insofar that the tracks were usually arranged using one sound module or another. Even when devices are compatible in the sense that they have adopted the same standard, hearing music on another device than the one the soundtrack was originally arranged for will cause some degradation, because the standards are only loosely specified in terms of timbre, volume levels, envelopes etc.

Some DOS games have specific arrangements for a variety of different kinds of MIDI devices for these reasons, with different mix levels and instrument setup, sometimes scaled down arrangements, adjustments for the instrument patches and even loading entirely new patches onto the devices.