A WTF Moment with the CAB block... :-)

M

Mark Al

Inspired
I was re-organizing my IRs in Axe FX-III this morning. After wiping out all of my custom IRs from the unit, all my patches' cab blocks now show <EMPTY> as expected. With that, some patches are dead silent (again as expected), but some patches are NOT, and somehow they sounds half decent, WITHOUT IRs!

And that is NOT what I'd expected. It turns out the reason that cab with <EMPTY> IR still "makes sound" is due to the non-zero "AIR" control in the "Room/Air" config. That piqued my curiosity, so I tried to dialed in a few patches this way with no IR, e.g.
1. 30% AIR, and tune AIR frequency up and down around 5K
2. Use "Preamp" FILTERS for low/high cuts.
3. Use the Amp block's speaker section to give the tone some "body".

Vola! It turns out this approach yield some quite balanced decent tone!

Now that I think about it, the Amp "Speaker" section is already sort of modeling the cab, adding an IR on top is theoretically redundant, isn't it? And with the <EMPTY> IR approach above, again theoretically, it took the mic completely out of the signal chain, and the resulting patch sounds very balanced.

The Amp Speaker section has dozens of Speaker Imp Curves to choose from, now I wish there are MORE of them :)

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From the wiki:

Air
Mixes some of the "direct" signal entering the Cab block with the "Cab-processed" signal leaving the Cab block. This adds some "air" to the sound, which some users find to add realism to the tone.

It's not supported on the AX8.

AIR FREQUENCY lets you adjust the cutoff frequency of the mixed signal. Increase the Frequency to its maximum value for a straight mix.

Tip: if you want to listen to just the "air" part of the signal, select an empty user cab, and turn up Air.
 
What you've stumbled upon is this:

A guitar speaker is sort of a "bad" speaker. It has a really limited frequency response compared to Full Range speakers like PA speakers. A steep drop-off above ~5k, and in the lows as well, and then coloration in the range it does produce. But it turns out that's exactly what you need to tame the noise of heavy distortion and get a listenable result.

You can use a PEQ to simulate a speaker IR as well (there have been posts on it, some from Cliff) By setting your high and low cuts, then tweaking your low and high responses to get something listenable.

You're using the Impedance curves just as a coloring EQ currently, but a PEQ you could tweak however you wanted.

And the Impedance curve is an EQ designed to layer on top of a speaker IR. The Speaker IR maps the Speaker and Mic tone and coloration, and the Impedance curve maps the coloration from your power amp being connected to a specific speaker. In the real world both happen, which is why the Axe also models both.

All that said, don't hold yourself to the real world, as much as some want to replicate their real world tones it's really just a game of "what sounds good", and don't let reality limit that.
 
Mark Al said:
I was re-organizing my IRs in Axe FX-III this morning. After wiping out all of my custom IRs from the unit, all my patches' cab blocks now show <EMPTY> as expected. With that, some patches are dead silent (again as expected), but some patches are NOT, and somehow they sounds half decent, WITHOUT IRs!

And that is NOT what I'd expected. It turns out the reason that cab with <EMPTY> IR still "makes sound" is due to the non-zero "AIR" control in the "Room/Air" config. That piqued my curiosity, so I tried to dialed in a few patches this way with no IR, e.g.
1. 30% AIR, and tune AIR frequency up and down around 5K
2. Use "Preamp" FILTERS for low/high cuts.
3. Use the Amp block's speaker section to give the tone some "body".

Vola! It turns out this approach yield some quite balanced decent tone!

Now that I think about it, the Amp "Speaker" section is already sort of modeling the cab, adding an IR on top is theoretically redundant, isn't it? And with the <EMPTY> IR approach above, again theoretically, it took the mic completely out of the signal chain, and the resulting patch sounds very balanced.

The Amp Speaker section has dozens of Speaker Imp Curves to choose from, now I wish there are MORE of them :)
Click to expand...

For clean tones, you don't necessarily need a Cab block. However, distorted tones are another story.
 
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