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ghost fizz


If they took the fizz out, there would be a ton of posts complaining that the sound was too sterile.

The cool thing is you get to choose how much of that you want:

As for the noise, that's noise coming from your guitar, being amplified by the high gain of the amp. You have choices here, too: either shield your guitar, remove the source of interference in the room, use the noise gate, or live with it. :)
Righty with real amp at those settings, there was a ton of noise coming from the amp (not the guitar). The Axe-fx model did not have that (that is a good thing). The Axe-fx does not emulate the self-noise of the amp.


Power User
To me this fizz thing doesn't sound as 'desirable' or musical. Then why should it be emulated? Same goes for noise.
To me, its an essential part of the sound. Plastic toys and Axe are different, and this is a huge part of the difference. Also, Axe has much less noise than amps, guitar induced noise it cannot change. Except with a noise gate of course...


To me, its an essential part of the sound. Plastic toys and Axe are different, and this is a huge part of the difference.
I agree - if the fizz was gone the amp would just end up sounding flat and sterile. The clip that I posted earlier was in the extreme just to show the "decaying fizz". The awesome thing about the Axe is that you can remove things that you don't like on the fly. This might just be a little harder to take away.


Fractal Audio Systems
The "fizziness" of clipping is determined by how "hard" the clipping is. There are three primary places that clipping occurs in a tube amp: the preamp tubes, the phase inverter and the power tube plates.

Preamp tube clipping can range from soft to hard depending upon the design. Phase inverter (PI) clipping, which is actually the power tubes grids clipping, is very hard. Power tube clipping ranges from soft to hard depending upon the amount of negative feedback in the power amp.

Preamp tube clipping is comprised of cutoff, which is soft, plus saturation, which tends to be hard. Actual saturation rarely occurs because most preamp stages are designed such that the grid clips before the tube enters saturation. Grid clipping is hard. Local negative feedback is used in the form of cathode caps to shape the response of a preamp stage. If there is no cathode cap then there is negative feedback at all frequencies which increases the hardness of the clipping. The last stage usually dominates the clipping. Some amps have no cathode cap on this stage, e.g. JCM800, and therefore have hard preamp clipping. The Axe-Fx II does not expose the negative feedback settings for the preamp stages to the user, these are hard-coded. Reducing the Triode Hardness parameter will soften the clipping more-or-less depending upon the particular amp model.

In a typical tube amp the power tubes start to clip right about the same time the PI/grid clipping occurs. This is intentional so as to get the most power from the tubes. However some amps are intentionally mismatched as the designer's intent was to get more power tube clipping than PI clipping (i.e. Trainwrecks). The Transformer Match parameter adjusts the relative onset of power tube vs. PI/grid clipping. Lower values will cause the PI/grid clipping to occur before power tube clipping. Higher values will cause the power tubes to clip before the PI. Note that the power tube plates follow the impedance curve of the speaker so while the PI/grid may be designed to start clipping first, this only occurs in the midrange. At frequencies above 1 kHz or so the power tubes clip first since the voltage on the plates increases as a function of the speaker impedance. The first thing to clip tends to dominate as once you enter clipping the effect of clipping elsewhere is diminished.

Negative feedback around the power amp attempts to linearize the transfer function. The more negative feedback the more the power amp is linearized. However this also causes the clipping to become harder. A power amp with no negative feedback will go into clipping softly. As you increase the negative feedback the "knee" gets sharper. The Damping parameter is the negative feedback control. Higher values give more feedback and harder clipping.

Presence and Depth work by modifying the negative feedback. As you increase them the feedback gets less so by turning up the Presence you get softer clipping in the power amp.

Therefore to decrease the hardness of the power amp clipping: reduce Damping, increase Presence, increase Transformer Match.
To reduce preamp clipping hardness reduce Triode Hardness.
There is no parameter exposed to adjust the PI hardness.

HOWEVER, the relative hardness of clipping is not all that audible. You have to listen closely. The IR is far more important in the final result. Some IRs let through a lot more high frequencies and therefore sound more fizzy.

Furthermore overanalyzing this is inadvisable. Many amps are specifically designed to clip hard as this gives a more aggressive tone that fits better in the mix. Some amps actually attempt to increase the hardness of the clipping as much as possible by using diode clipping or using very high values of negative feedback (i.e. Modded Marshalls, Camerons, 5150 III). Listening at low levels fools your ear. Our ears are more sensitive to midrange at low listening levels. This means we hear the clipping differently than when listening at the actual level the real amp would be generating.


Yes this has been a great thread. I just noticed this fizziness this week, I hear it in my CLR, but not so much in my NX-12. I was worried I had a bad CLR, this thread has not only allayed my fear of that, but learned a lot! Thanks all.


Fractal Fanatic
Truly enjoying this thread, and witnessing Cliff's expertise (and patience!).

Cliff, you should consider writing a book, someday (because, of course, you have time for that...).


The really funny thing here is, for whatever reason, in the preset given doing the opposite of what Cliff suggests for reducing that hardness of the clipping actually reduces the static effect with the volume rolled down - dramatically



totally awesome! thanks for the technical breakdown Cliff. that answered all of my questions for sure.

if you listen to that clip, he has plenty of that fizz....to me it sounds more obvious than my clip did, and i had more gain....which just goes to show you how clean the axe-fx really is.


The really funny thing here is, for whatever reason, in the preset given doing the opposite of what Cliff suggests for reducing that hardness of the clipping actually reduces the static effect with the volume rolled down - dramatically

please post the settings or the preset, cause that rocked!
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