When I use headphones, the sound comes out distorted. Voices sound as if they were far away, while instruments that should be in the background sound enhanced.
When I play songs with the laptop's integrated speakers everything is alright, and the headphones work normally when plugged into another computer.
I tried reloading ALSA and reinstalling some of the related packages, but nothing worked.

I'm using Xubuntu 12.04 32-bit.

Thanks to anyone who will suggest me how to solve this problem.