Originally posted by ^Chacron^
Trendkillah in answer to your question I'm recording my using my les paul and Marshall amp, the 'Output' lead goes directly to my soundcard.

The fizziness you're hearing is basically because you don't have a guitar speaker anywhere in there. The speakers in a guitar amp don't reproduce high frequencies very well at all; if you used a microphone in front of the amp and fed that to the soundcard you'd probably find it sounds very different.

There are a couple of things you could try:

1) Do some EQing - take out the higher frequencies, particularly over about 4-5kHz.

2) Get some sort of speaker simulator or amp modeller - they're intended for what you're doing and reproduce the frequency response of a guitar speaker.

Either of these approaches should tame that fizziness nicely. You might find a simple speaker simulator on EBay or similar. The Award Sessionmaster that I used to have was pretty good for this; it's basically an overdrive box with a 12" speaker simulator built in. Some of the Sansamp boxes do the same thing.