Here's what I posted recently in
another thread:
Having been involved with many others in the ridiculous Line 6 PodXT fizz debate, I think it's important to differentiate between 3 very different types of things that people call fizz (there may be more).
(1)
Digital distortion is something that needs to be avoided and removed completely before even considering the quality of modelled overdrive. Extreme digital distortion is obvious, but it can be easily overlooked if you're only occasionally just hitting the digital limit on brief signal peaks. Clean and "on the edge of breakup" tones need lots of clean headroom by setting their patch output level low. It also means you'll need to set your overdriven patches at a much lower level if you want consistent volume across your patches. For some equipment (not necessarily the AxeFX) that has a maximum output level of around 0dB, you may need to use a signal booster to to your power amp, obviously taking care with how your power amp handles its own signal peaks.
(2)
True Overdrive is the normal and natural overdrive produced by both real and modelled amps and overdrive pedals. It's common to see newbies (with little or no experience or real amps/pedals) jump in on a debate about fizz after turning up their drive for the first time and announce that their unit is also defective, because they can hear the fizz problem. True overdrive is integral to the signal - it's connected in the sense that it contains emphasised higher harmonics of the note being played as well as lower notes caused by inter-modulation between multiple notes as well as the harmonics themselves. With high treble boost settings this can be quite nasty and gritty, but it's still "normal".
(3)
True Fizz IMHO is stuff that's produced in the modelling process that's not connected with what you're playing, not present in the original amp being modelled, and not filtered from the modelled signal. The most obvious and probably the most objectionable is aliasing distortion. This is a digital artefact common in cheap and/or poorly designed modellers (not the AxeFX). Another problem common in cheap modellers is high end “junk” produced by their overdrive algorithm that cannot be properly filtered with their simplistic speaker filters. A real guitar speaker typically has a very steep blocking filter in the 4 – 6KHz region, with higher frequencies at least -20dB lower.
Hope this adds some clarity.
I thought of another one ...
(4)
Fret Buzz - kills mostly the fundamental of your notes, kills tone, kills sustain, sounds buzzy on clean settings. Adjust your guitar so it doesn't do this at your strongest picking strength IMHO.
