The problem I was having wasn't that the midi file was fading out too fast; instead the file wasn't fading out at all. As a point of fact, it doesn't matter what volume parameter I pass to media_loop() to begin with, because the midi file will always play at the same volume.

This may not be a universal problem, perhaps only certain midi files (or certain computers). The manual says that if the audio mixer has no synthesizer channel, then it won't effect volume - well my computer doesn't have a synthesizer channel so there you go. I don't want people without this channel in their mixer to have a different sound experience, than those that do.

The master_vol variable will have to work, because its the only thing that effects the volume of these midi files, without any caveats. Because of the simplistic audio needs of my game, there won't be any noticeable problems caused by the use of the master_vol variable.

Another alternative solution would be to convert all of my .mid files into .mp3, because media_tune WILL change the volume of these files under all circumstances. But that would significantly increase the size of the finished game's folder with no payoff in improved sound or anything like that.

Thanks for the input.