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Axe-Fx III Firmware Version 11.00 Public Beta

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FractalAudio

Administrator
Fractal Audio Systems
Moderator
I read the description and I downloaded it but I'm just not understanding what this does. Does it only effect with cab sims on?
No.

A tube power amp is a transconductance amplifier, voltage in - current out. A speaker is a voltage transducer, voltage in - sound out. Since the power amp is driving current the voltage at the speaker is the current times the impedance of the speaker (Ohms law V = I*R). The voltage therefore is dependent upon the impedance.

A solid-state power amp is a voltage amplifier, voltage in - voltage out. Since the power amp is driving voltage the voltage at the speaker is NOT dependent on the impedance of the speaker.

When an IR is captured (correctly) it is done using a solid-state power amplifier so the effects of impedance do not influence the measurement. Some people try to use tube power amps to capture IRs. This is incorrect methodology.

The Axe-Fx power amp simulation is a transconductance simulation. It uses a simulated speaker impedance to derive the output voltage that then drives the simulated cabinet (IR).

Firmware 11.xx has 47 (and counting) speaker impedance curves that you can select that allow for different power amp transconductance responses. Moreover the impedance simulation is now a high-order network that simulates the perturbations in impedance due to cabinet resonance.

If you are using a conventional guitar cab and solid-state power amp ideally you would want to know the impedance curve of the cabinet. This requires special test equipment although I'm working on a idea to use the outputs of the Axe-Fx directly along with a special cable to allow field measurements by users. At this time the impedance curve matching is a Matlab program though and requires some hand-tuning.
 

shatteredsquare

Power User
hey when you plug a cab into a power amp, and you get resonance points from frequency nodes to start effecting output frequency response dynamically...based on the physical dimensions of the wooden box the speakers are mounted in...that's acoustic. like a coke bottle. acoustic interaction! can u believe it?? like acoustic coupling with guitar pickup feedback, just at the other end of the rig.
 

VidarAus

Inspired
No.

A tube power amp is a transconductance amplifier, voltage in - current out. A speaker is a voltage transducer, voltage in - sound out. Since the power amp is driving current the voltage at the speaker is the current times the impedance of the speaker (Ohms law V = I*R). The voltage therefore is dependent upon the impedance.

A solid-state power amp is a voltage amplifier, voltage in - voltage out. Since the power amp is driving voltage the voltage at the speaker is NOT dependent on the impedance of the speaker.

When an IR is captured (correctly) it is done using a solid-state power amplifier so the effects of impedance do not influence the measurement. Some people try to use tube power amps to capture IRs. This is incorrect methodology.

The Axe-Fx power amp simulation is a transconductance simulation. It uses a simulated speaker impedance to derive the output voltage that then drives the simulated cabinet (IR).

Firmware 11.xx has 47 (and counting) speaker impedance curves that you can select that allow for different power amp transconductance responses. Moreover the impedance simulation is now a high-order network that simulates the perturbations in impedance due to cabinet resonance.

If you are using a conventional guitar cab and solid-state power amp ideally you would want to know the impedance curve of the cabinet. This requires special test equipment although I'm working on a idea to use the outputs of the Axe-Fx directly along with a special cable to allow field measurements by users. At this time the impedance curve matching is a Matlab program though and requires some hand-tuning.
Does this mean the cabinet resonance should be known for every IR used and set accordingly in the Amp Block for best results? I don’t know the resonance of the cabs captured in almost all the IRs I use.
 

Klausi

Inspired
Great feature. Improved some patches within minutes. But when I select one of the cabinets and switch back to DEFAULT I get the linear default and not the initial curve.
 

shatteredsquare

Power User
Does this mean the cabinet resonance should be known for every IR used and set accordingly in the Amp Block for best results? I don’t know the resonance of the cabs captured in almost all the IRs I use.
there's so many cabs measured, just pick the one closest to the IR you've got loaded, it will hum the same way (same/similar dimensions)
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
Great feature. Improved some patches within minutes. But when I select one of the cabinets and switch back to DEFAULT I get the linear default and not the initial curve.
What do you mean by "DEFAULT"? There is no DEFAULT cabinet type.
 

creativespiral

Inspired
This is awesome Cliff! Your rate of innovation is unmatched!

I'm wondering, as you're applying these cab impedance modeling upgrades, is there anything planned for changes to Variable Input Impedance on the Input 1?... To further improve modeling the relationship of first block effect with guitar pickup? I don't use it a ton, but the ZVex Fuzz Factory is one of those pedals that has really interesting fuzz stability tied to impedance. The beginning of Plug In Baby by Muse is a good example.
 

Perdikament

Power User
So when we are mixing Cabs in the cab block, say for example, (& to pick two that would be quite different) the 4x12 Rumble cab & the 1x12 Carol Ann, we would have to pick one of the impedance maps, or can each cab in the cab block have its own individual? I’m guessing no, cause that would be basically like running up to four Power Amp sections at the same time.
 

DLC86

Fractal Fanatic
While scrolling thru the cabinets I noticed there are some which are not affected by the cabinet resonance parameter, is this normal?

They're:
2x12 Bassguy
2x12 Jazz 120
4x10 Brit JM45
4x12 Hipower
 
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