Process priority of music player? I have a Samsung Galaxy S+ with Cyanogenmod 10.1 (built 2013-04-15) (Kernel 3.0.73-rc1-PhenomKernel-V3) and music playback is stuttering when the phone is locked/standby most of the time.

Some days it's fine being locked and playing music, other days it can't play 5 seconds straight.

As soon as the phone is unlocked music plays fine, when locked again the stuttering continues.

I've tried solving this problem by trying around with different I/O schedulers (currently on ROW which was the ROM's default) and CPU clock rates (currently set to 192-1401 ondemand, tried elevating the minimum clock to up to 386 MHz) to no avail.

Since the phone is single core, my best guess is that the phone goes into the powersave governor when locked and some background processes are using all the processing power when syncing data or doing something similar. Is this a correct assumption?

If so, how do I give the music player a higher process priority (e.g. lower its nice value) or otherwise tell the system to prefer spending resources on music playback?
I believe why this is happening is because when your phone goes into standby the processor goes into a state where the processor slows down to save battery life. You could try to see if there is a feature in your mod to turn off this mode. 

I think your phone doesn't go into power saver mode when it is plugged in, try that and see if it works (this solution is less convenient because your phone needs to be plugged in). One last thing I could think of would be trying to kill some services that are hogging cpu. This solution will be more likely to drain your battery if you kill some services that automatically start up again. 

Good luck!