God Of War Ghost Of Sparta and Chains of Olympus

[TheDax]

To elaborate a bit more, games were designed on the PSP with 222mhz in mind, though some request up to 333mhz for better performance. If you underclock the virtual PSP by going below 222, it can cause internal FPS drop, like vsub_ said, or other issues like audio stuttering. A lot of the games don't care too much, but the closer to 0 you get, the worse they'll perform (though keep in mind 0 is auto/lets the game decide, so don't be scared to put it back to 0 if you feel you messed up). There's usually a happy medium between emulation performance and virtual CPU speed. What that happy medium is depends on your device, and the game.

Audio stuttering can also be caused when the game isn't going at full speed, even if you had the virtual CPU clock at 222 or 333. If your device just isn't strong enough to run the game at full speed, audio problems will result since things get slower and choppier. Some emulators have what's called time stretching, where it'll lower the pitch of the audio and slow it down, so it still sounds smooth when games get choppy, but PPSSPP doesn't have such a feature yet.

Finally, if it's not caused by low virtual CPU speed, or your device being weak, it's probably an emulation bug. Our audio code still isn't perfect either, so some popping could result in some events taking too long, or not taking long enough (if the game expects to have things done at a certain time, we might be doing them too quickly).