Suddenly? The sound might be wrong because I used the incorrect version of this emulator, but I figured either the whole thing was wrong, or the whole thing was right. I didn't think there was any type of sudden change. Where in the video is it?

arronmunroe Sometime before the levels with the pipes.

TimelordR I think a better question would be what exactly do you mean by BGM deteriorating. What makes the music sound weird?

arronmunroe Not to go into technical detail, but the BGM was beginning to sound weird & off-key, despite the game running without flaws.

TimelordR I think the problem first shows up around the first boss which is round 12. I would describe the problem as being that one or more instruments are missing. I compared 5:28 last bad guy escaping music to 8:23. It's strange that it happens part way through the game, but I think the problem is what I said originally, that I used the wrong version of MAME. I do plan on recording the Namco Classics again sometime and when I do, I'll make sure the music isn't off. Edit: OK, I might see the off-key thing in the music (at least for bad guy escaping music), but still no doubt an emulator version problem.