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I'm using Rakarrack in Linux Ubuntu 12.04. In the laptop, sometimes I hear "clicks and artifacts", in a desktop PC things get worse with plenty of noise (If I plug the headset at high volume, I can hear the circuitry noise when accessing data in the disk, or moving the mouse, etc.).
I guess that I should have a PC with a sound card different than the internal audio that comes from factory. Now, which are the options? I mean, how do I know which audio cards are fully supported by Ubuntu 12.04?
Besides that, do I need hardware filters or something like that?
Probably the best bet is a USB audio interface. Behringer products are pretty well supported in Linux.
The problems you describe sound like problems caused by things outside of Rakarrack,and Rakarrack is faithfully amplifying or reproducing what is coming in.