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WALKTHROUGH: Dialing in amps on the Axe-Fx

fuzznut

Member
#23- damp... IIRC, higher values (CW) result in less damping, at least that's what I hear. Like going CW is increasing the value of the feedback resistor. But zero (fully CCW) disconnects the feedback loop for no damping at all. Cliff?
 

fuzznut

Member
Jay Mitchell said:
fuzznut said:
#23- damp... IIRC, higher values (CW) result in less damping,
No, it's the opposite.
OK, but as I go CW and increase damping, the volume also increases. As you know, more damping = more feedback = less gain = less volume. So I guess what I'm hearing is the volume compensation that Cliff included in the damp parameter.

BTW, great job Yek!
 

yek

Moderator
Moderator
Re: Dialing in an amp/cab on the Axe-Fx: Walkthrough

:?:
eda123 said:
AWESOME!!!

THANK YOU SO MUCH!! Very helpful for a newbie like me, and the step-by-step method just cant be beat for clarity.


Some questions:

For #7 - can you post a link here on how to dial in live vs. bedroom? Im sure there is some article out there outlining this- if so a link would be helpful.

For #20 -
If you turn it up beyond the amount that the amp sim can handle, the tone will get mushy, or bass tones will get farty and flubby.
Is there any more info on that? IE, why this happens, what models it happens with and at what settings, etc?
Bedroom/live: when playing at soft volume, you often turn up treble and bass. It's what the Loudness switch does on older hifi systems. At louder level those bass/treble freqs are much more noticeable by the ear (Fletcher Munson-law or something) and those same settings can be too much. Also, the guitar is a Mids-instrument, it'll disappear in the mix when competing with other instruments below or above the Mid-range. There's no guide as to dealing with this at bedroom level, other than experimenting yourself. As soon as things work out at rehearsal or live, restrain yourself from adjusting the tone at home. One handy trick though is using the blocking PEQ described above.

MV: no strict guideline here either. Just be aware of it happening.
 

Jay Mitchell

Fractal Fanatic
Deltones said:
It would be great if somebody could chime in about a way to hear what happens when the frequency is right while tweaking that parameter.
I explain this in the thread on speaker resonant frequency: there is no "right" frequency, and there is no way to identify the actual resonant frequency of a speaker (or cab sim) by ear.

It seems that this parameter is very important for accuracy.
Also explained in the other thread. It is usually negligible and at most a second-order effect. You may actualy prefer the sound of this parameter set to something other than the "correct" frequency, if you can even tell the difference.

If you're looking for the "missing piece," this ain't it. It's a subtle enhancement that is best taken care of only after all the heavy lifting has been done.
 

eda123

Inspired
Re: Dialing in an amp/cab on the Axe-Fx: Walkthrough

yek said:
:?:
eda123 said:
AWESOME!!!

THANK YOU SO MUCH!! Very helpful for a newbie like me, and the step-by-step method just cant be beat for clarity.


Some questions:

For #7 - can you post a link here on how to dial in live vs. bedroom? Im sure there is some article out there outlining this- if so a link would be helpful.

For #20 -
If you turn it up beyond the amount that the amp sim can handle, the tone will get mushy, or bass tones will get farty and flubby.
Is there any more info on that? IE, why this happens, what models it happens with and at what settings, etc?
Bedroom/live: when playing at soft volume, you often turn up treble and bass. It's what the Loudness switch does on older hifi systems. At louder level those bass/treble freqs are much more noticeable by the ear (Fletcher Munson-law or something) and those same settings can be too much. Also, the guitar is a Mids-instrument, it'll disappear in the mix when competing with other instruments below or above the Mid-range. There's no guide as to dealing with this at bedroom level, other than experimenting yourself. As soon as things work out at rehearsal or live, restrain yourself from adjusting the tone at home. One handy trick though is using the blocking PEQ described above.

MV: no strict guideline here either. Just be aware of it happening.
Thanks Yek! Again, Im really enjoying this and all of your How-To's on the Wiki. Great service to this forum!!
 

GiRa

Power User
Great stuff!

The Yek's how-tos page on the wiki is becoming pretty huge, maybe it's time to split it in more pages.
 

Deltones

Experienced
Jay Mitchell said:
Deltones said:
It would be great if somebody could chime in about a way to hear what happens when the frequency is right while tweaking that parameter.
I explain this in the thread on speaker resonant frequency: there is no "right" frequency, and there is no way to identify the actual resonant frequency of a speaker (or cab sim) by ear.

It seems that this parameter is very important for accuracy.
Also explained in the other thread. It is usually negligible and at most a second-order effect. You may actualy prefer the sound of this parameter set to something other than the "correct" frequency, if you can even tell the difference.

If you're looking for the "missing piece," this ain't it. It's a subtle enhancement that is best taken care of only after all the heavy lifting has been done.
Yeah, I read the other thread afterward. Still very good stuff, even if it ain't the missing piece :mrgreen:
 

joegold

Fractal Fanatic
Jay Mitchell said:
Deltones said:
It would be great if somebody could chime in about a way to hear what happens when the frequency is right while tweaking that parameter.
I explain this in the thread on speaker resonant frequency: there is no "right" frequency, and there is no way to identify the actual resonant frequency of a speaker (or cab sim) by ear.

It seems that this parameter is very important for accuracy.
Also explained in the other thread. It is usually negligible and at most a second-order effect. You may actualy prefer the sound of this parameter set to something other than the "correct" frequency, if you can even tell the difference.

If you're looking for the "missing piece," this ain't it. It's a subtle enhancement that is best taken care of only after all the heavy lifting has been done.
I don't have time to search for the quote but...
Yet in one of Cliff's recent posts he basically says that tweaking the SRF just right *was* the missing piece in a tone he was trying to nail.

EDIT: That's why there's all this chatter again around here about the SRF parameter.
 

Jay Mitchell

Fractal Fanatic
joegold said:
I don't have time to search for the quote but...
Yet in one of Cliff's recent posts he basically says that tweaking the SRF just right *was* the missing piece in a tone he was trying to nail.
That's not what he said. Here's the quote:

"Furthermore there are certain aspects that simply can't be modeled and require user intervention. For example, a speaker has a low-frequency resonance. A tube amp will create a higher output at that resonant frequency. The Axe-Fx has no way of knowing what that resonant frequency is and defaults to a value that is common for the speakers that are typically used with that amp. However, if you drive that speaker through a solid-state amp you won't excite the resonance unless you adjust the LF Resonant Frequency to match it. This is the one of the few advanced parameters I ever adjust and I tweak it until I hear the bottom end "sympathize". For example, my favorite Mesa cab resonates around 110 Hz but most of the models default to 95 Hz so I usually adjust the LF Resonance to 110 Hz when using that cab. After I do that the Axe-Fx is indistinguishable from the real thing, IMHO."

If you're close enough that you can't distringuish between the Axe-Fx and the real thing after you get the resonant frequency correct, the odds are that you couldn't tell the difference with a differenct value of resonant frequency.

It really is a subtle effect, when it's even audible.
 

joegold

Fractal Fanatic
Jay Mitchell said:
joegold said:
I don't have time to search for the quote but...
Yet in one of Cliff's recent posts he basically says that tweaking the SRF just right *was* the missing piece in a tone he was trying to nail.
That's not what he said. Here's the quote:

"Furthermore there are certain aspects that simply can't be modeled and require user intervention. For example, a speaker has a low-frequency resonance. A tube amp will create a higher output at that resonant frequency. The Axe-Fx has no way of knowing what that resonant frequency is and defaults to a value that is common for the speakers that are typically used with that amp. However, if you drive that speaker through a solid-state amp you won't excite the resonance unless you adjust the LF Resonant Frequency to match it. This is the one of the few advanced parameters I ever adjust and I tweak it until I hear the bottom end "sympathize". For example, my favorite Mesa cab resonates around 110 Hz but most of the models default to 95 Hz so I usually adjust the LF Resonance to 110 Hz when using that cab. After I do that the Axe-Fx is indistinguishable from the real thing, IMHO."

If you're close enough that you can't distringuish between the Axe-Fx and the real thing after you get the resonant frequency correct, the odds are that you couldn't tell the difference with a differenct value of resonant frequency.

It really is a subtle effect, when it's even audible.
Fine. You're right.
Cliff didn't say "After I do *that* the Axe-Fx is indistinguishable from the real thing, IMHO."
Lol.
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
The SRF parameter makes a difference in certain circumstances: medium-gain with lots of power amp breakup and high-gain into a traditional guitar cab.

For example, a Deluxe Reverb easily gets into power amp breakup with a Drive of 5.0. Play a G chord and listen to the low notes breaking up. Adjust the SRF and you'll hear the character change pretty dramatically. This applies to both FRFR and traditional speaker applications.

For high-gain amps into a traditional cab the SRF has a definite effect for palm-mutes and diad chugging. As you excite the resonant frequency the speaker excursion increases and you get much more punch. This even applies a bit to low and medium gain amps if you rely on that punch as part of your tone. Note, however, that the punch is rarely audible to the audience or captured during recording.

One way to find the SRF is to put a Filter block after the amp block. Set the type to Peaking, Q to 5 or so and Gain to 10 dB. Start with a Freq. of 50 Hz. Play some chugga-chugga and slowly adjust the Freq. until you hear and feel the cabinet resonate. Make a note of the frequency. Remove the filter block and set the amp block SRF to match. 4x12s typically have an SRF of between 80 and 120. Open back cabs are typically a bit lower.
 

Deltones

Experienced
FractalAudio said:
One way to find the SRF is to put a Filter block after the amp block. Set the type to Peaking, Q to 5 or so and Gain to 10 dB. Start with a Freq. of 50 Hz. Play some chugga-chugga and slowly adjust the Freq. until you hear and feel the cabinet resonate. Make a note of the frequency. Remove the filter block and set the amp block SRF to match. 4x12s typically have an SRF of between 80 and 120. Open back cabs are typically a bit lower.
Is this for physical cabs only, or we can use your trick with IR's (stock or Redwirez)?
 

Jay Mitchell

Fractal Fanatic
Deltones said:
Is this for physical cabs only, or we can use your trick with IR's
It will not work at all with IRs, because the impulse response contains no impedance information. Furthermore, it cannnot work with a physical cab unless it is being driven by an amplifier that either has a high linear source impedance (for example, a Vox AC30 or a Champ) or is being driven to the point of saturation of its power stage. Even then, the notion that you can hear the "resonant frequency" apart from all the other response peaks that guitar speakers have (due, for example, to standing waves in the enclosure) is a very tenuous one.

The typical notion of "resonance" as something akin to the vibration of the top or strings of a guitar is completely off base with a loudspeaker. A speaker being driven by a low-impedance source does not resonate, and no amount of playing around with filters will enable you to identify the "resonant" frequency by ear. In a reflective acoustic environment, any apparent sympathetic vibration you hear is more likely to be due to standing waves in the room than to anything intrinsic to the speaker.

The response of amost every guitar speaker rolls off at a frequency well above the "resonant frequency" of that speaker mounted in a cab. Exceptions to this are speakers that were derived from woofer designs, e.g., EV EVM transducers. In an appropriately-designed enclosure (of the sort that you won't get if you're buying a guitar cab), it is possible - under ideal circumstances - to get such a speaker's response to extend downward to a frequency that is close it the resonant frequency of the cab. In an ideal closed-box design, the cutoff frequency (-3dB point) is equal to the resonant frequency of the speaker/enclosure combination. In a non-ideal situation - pretty much everything we're discussing here - that cutoff frequency will be quite a bit above the "resonant frequency."

Edit: I just took a look at several IRs of guitar speakers. Without exception, the response levels at their resonant frequencies are substantially lower (by as much as 12dB) than the highest levels within the octave immediately above this frequency. If you look for "resonance" by ear, you'll most often land on a frequency that is well above the actual resonant frequency.
 
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