> Noob question: this improves music/sounds of all games in MAME or just a few ones?
It should remove 90%+ of pops and crackles and distortion you may have heard as MAME attempted to mix down audio (sound effects and music) into mono or stereo in all games in MAME. There's a limiter now that prevents drivers from overdriving the mixer (which causes digital distortion and pops). We've started fixing drivers not to do it at all, but that won't be a quick process.