There's something that's been bugging me. On the last level of Dr. Jekyll and Mr. Hyde, there's a point in the game when the processor speeds up. It happens only on one part, and that's when you get to the first singing lady. Also, it doesn't happen all the time. It speeds EVERYTHING up, the barrels, the lady, music notes from the lady, and your character. Why would this occur? Any ideas?
Sounds like a bug in the game, especially if it only happens sometimes. Maybe the game is polling $2002 to time the frames, rather than using NMI at that particular part? I kinda doubt it (should be the same timing method as the rest of the game), but I dunno.
I really doubt there's any actual processor speed change here, as the CPU has a fixed clock and there is no way to change that in software. It's much more likely that this is just a bug, as Memblers said. I don't think it's due to pooling $2002 though, since missing VBlanks would actually make the game slower... We'd have to take a look at that part of the game while it's running to have a better idea, though. But that game does not seem very fun, as the angry Nintendo nerd advised. =D
Um... did you test this on a real NES?
It actually only happens on an NES, and not on an emulator. That's why this is posted in the NES Hardware forum ;)
EDIT: Though I didn't try the game in Nintendulator or Nestopia, so perhaps it does in those?
I don't have enough time to play-test the game in Nintendulator/Nestopia right now (*cough cough*
Caltech*cough cough*), but ... is your NES in good working order, and is the cartridge clean?
EDIT: Another stupid question, but maybe this is an NTSC/PAL mixup?