LPD - And Now For Something Completely Different....

groovenut

Power User
In this thread this morning http://forum.fractalaudio.com/axe-f...krod-model-how-dare-i-doubt-2.html#post712632, InsideOut and I had started a conversation about the TMA blocks in Cliffs presets and whether the information in the TMA contained the speaker cab IR information as part of it. I had asserted that if an IR of the speaker cab being used in the amp match was used during the TMA matching process (was part of the signal chain), that what was contained in the TMA after the match process was essentially only the amp information. Damn. Now I know I have to read that again, hopefully it makes sense.

The bottom line however is this, if you take my Splawn Quickrod presets or any of Cliffs TMA presets and bypass the cab, you can use a FRFR PA and any guitar cab of you choice.

So to back up my assertion, I did an experiment during my amp match session from http://forum.fractalaudio.com/axe-f...-adventures-tone-matching-stuff-part-2-a.html.

After I had completed the amp match process, in which I used an IR of the actual physical guitar cabinet, I recorded the AxeFx II playing through a FRFR PA and my favorite Avatar Celestion loaded 2X12 guitar cab (the same one I used during the amp match) with the cab sims globally bypassed. I then recorded the AxeFx II direct with the cab sims globally activated. Here are the results



Here is what the two look like compared within a frequency spectrum analyzer.

CabDirectComparison.jpg


The light blue is the physical cab take, the purple is the IR take. Almost exactly the same. I believe the very small differences are in playing between the takes.

It conclusion it appears to my ears and eyes that there is no perceivable difference in the two samples.

Please chime in and let me know your thoughts!
 
Alright. I'll let my ears take a shot at this: First of, the tone itself is spot but...

to my ears the first clip has a bit of upper mids or less low-mids and low frequencies. Or the second clip has more low-mid to low end frequency. However the upper mids I hear in the first clip could be the same due to the bottom/low-mid frequencies are now involved in the second clip. If that makes any sense to you Lawrence. But the graph contradicts my ears in reference to the clips as far as the low-mids and bottom end goes. As soon as you add or take away a frequency it can be somewhat deceptive to the ears as it draws more emphasis onto other frequencies in the spectrum.
 
Alright. I'll let my ears take a shot at this: First of, the tone itself is spot but...

to my ears the first clip has a bit of upper mids or less low-mids and low frequencies. Or the second clip has more low-mid to low end frequency. However the upper mids I hear in the first clip could be the same due to the bottom/low-mid frequencies are now involved in the second clip. If that makes any sense to you Lawrence. But the graph contradicts my ears in reference to the clips as far as the low-mids and bottom end goes. As soon as you add or take away a frequency it can be somewhat deceptive to the ears as it draws more emphasis onto other frequencies in the spectrum.
Oh yeah for sure. I find it interesting that the open air speaker has slight frequency boosts in the sub 40Hz range and ~350Hz.

The main point of this experiment was to prove that if you use the cab IR of the physical cab during the amp match process, you can eliminate it when you use an actual guitar cab with a power amp. The info in the TMA is only for the amp.
 
In this thread this morning http://forum.fractalaudio.com/axe-f...krod-model-how-dare-i-doubt-2.html#post712632, InsideOut and I had started a conversation about the TMA blocks in Cliffs presets and whether the information in the TMA contained the speaker cab IR information as part of it. I had asserted that if an IR of the speaker cab being used in the amp match was used during the TMA matching process (was part of the signal chain), that what was contained in the TMA after the match process was essentially only the amp information. Damn. Now I know I have to read that again, hopefully it makes sense.

At the risk of sounding like a fool I have been hesitant to ask this.........but I so don't have a grip on this process....so taking an IR of the cab used for the TM and putting it in the signal chain some how cancels the physical cabinet out and what you are left with is just the amp match?

Oh and by the way thanks very much for your stellar contributions here!!!!
 
Sorry to ask, what do you mean by " I recorded the AxeFx II playing through a FRFR PA and my favorite Avatar Celestion loaded 2X12 guitar cab"? Which is it? FRFR or through cab?
 
Sorry for the confusion. Long form..." I recorded the AxeFx II playing through a full range flat response power amp and my favorite Avatar Celestion loaded 2X12 guitar cab"?
I hope that clears it up.

Guys, please don't apologize for asking questions. I firmly believe that within reason there are no stupid questions. I post this information so we can all get a better understanding. When people ask questions it's an opportunity for all of us to learn.
 
At the risk of sounding like a fool I have been hesitant to ask this.........but I so don't have a grip on this process....so taking an IR of the cab used for the TM and putting it in the signal chain some how cancels the physical cabinet out and what you are left with is just the amp match?

Oh and by the way thanks very much for your stellar contributions here!!!!

Yes that appears to be true from the results of my experiment. We are presenting the TMA block with roughly the same info as is being created in the physical world. After the TM is taken, bypassing the cab block would be the same as removing the physical speaker cabinet and we are left with just the amp signal.

I am going to try to compare the direct signal from the amp with the signal from the AxeFx (cab block bypassed) to see if I can verify this with hard data. The frequency analysis in the OP seems to back this up and I would like to get a FFT plot to confirm the direct signals are the same.
 
I agree with swass on the tone analysis but it is ever so slight and doubt you would hear this in the context of a mix but never the less it is impreissive. I would like to see the spectrum analysis at a higher resolution though, if you can increase it to say 3dB per graduation that would make it better to really take it apart.
 
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Agreed! The next time I perform this experiment, I will use a re-amp track so the input stimulus is the same for both examples as well.

Just to reiterate, the point in posting the examples was to illustrate that removing the cab block from the amp/cab/TMA string allows just the matched amp information to remain. Allowing the use of any cab IR you wish, or the use of a power amp/guitar cab. While it is not exactly the same in this example, it is within the span of tolerance. I will post a FFT of the direct signals shortly for comparison.

Thanks so much for the feedback!
 
Thanks for the response man. I am not sure why I am having such a hard time wrapping my mind around this. I am sure it probably just because I am trying to understand it in theory as apposed to by practice. I may have to borrow an amp and experiment around with it a bit myself (I am no longer an amp owner). It will likely be a huge "DUH" moment when the concept becomes clear to me.....Wow if I had a nickle for every one of those moments HA HA.

At any rate I am glad I stumbled across this thread. It is interesting to say the least. I will continue to follow your progress.

Thanks Again
 
Sorry for the confusion. Long form..." I recorded the AxeFx II playing through a full range flat response power amp and my favorite Avatar Celestion loaded 2X12 guitar cab"?
I hope that clears it up.

Guys, please don't apologize for asking questions. I firmly believe that within reason there are no stupid questions. I post this information so we can all get a better understanding. When people ask questions it's an opportunity for all of us to learn.

Thanks for clearing that up. FWIW, PA normally means "Public Address", not Power Amp, and refers to the complete chain [Power amp]>[Speakers]. This is what threw me and left me confused. Thanks for clearing that.
 
Anyone have any insight as to why the cab response was so different to the IR take in the low end? I have been trying to figure that one out and the only thing I can think of is ether the mic that was used or an EQ some where in the signal chain.
 
Just for the presentation of clear info:

The mic used to capture the IR was not changed or moved during the entire amp match process.
The levels were not changed during the entire IR capture/amp match process.
There was no change in the signal chain during the entire IR capture/amp match process.
There was no EQ in the signal chain, nor any applied post capture.
The mic used was an Audio Technica AT4050 with the pattern set to cardioid, flat response (no LF rolloff), and no pad.
The mic placement was at dust cap edge, 6 inches from the grill.
The mic preamp was a FMR Really Nice Preamp.

I do try to follow the scientific method as much as possible :D
 
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Here's my theory...

The take that was done with the IR was recorded direct with no sound in the room, ie monitored through headphones.

The take that was done with the real cab was recorded with me standing in the room with the cab.

I believe what we are seeing and hearing in the sub 40Hz and 350Hz boost is the interaction between the sound pressure level in the room and the guitar/pickup. Obviously there would be some resonant response from the guitar to the sound pressure level (also why it's easier to get controllable feedback with open monitors).
The only real way to prove this supposition would be to redo the experiment with the real cab take void of the sound pressure level interaction.

Coming soon! (because I am obsessive about details :) )
 
I really interested in your outcome here.i tried recording from the fx send but lost a little in the tm because of the lack of the amps power section.
 
Very interstin thread. And yes, it is lika a equation: [physical Amp] + [physical Cab] + [Mic.&position] = [Amp Block] + [TMA] + [CAB IR]. If [CAB IR] = [physical Cab] + [Mic.&position] they should be theoretical be identical, so we can cut that out from the equation. But we have still differences: Practical we still have used a SS Amp to capture the CAB IR (and we all know FRFR is a theoretical assumption). The oher thing is: When recording the guitar track from the in the room miced cabinet we capture also the whole early reflection which getting lost in a 42ms Impulse response... i think these two issues does make the little differences in your frequency curve. But man: the only noticable differences are beetwenn 0 and 40Hz ... absolutely irrelevant differences!

I love the sound of your Splawn ... did you post your Avater Cab IR ???? I will try that sound myself ... like it much! which guitar you used here?
 
Sounds spot on to me.

I'm getting a bit more "woof" from the real cab which is reflected in your spectrum graph. But it's down below 40Hz and my setup here has a subwoofer and it's cranked. In almost all cases you'd high pass the guitars at some value much higher than that anyway.
 
After playing with the TMA and CAB blocks and matching I think I've got my brain around all this and what is happening where.

If you shoot an IR of the cab and then use the matching template indeed the only info in the TMA is the amp info; the only differences in the chain are the amps. The output chain after that is the 'same' (real amp thru mic'ed cab, or AFX amp thru IR of miced cab). You can change the cab/mic IR's afterwards 'properly' with this method. This is method one in the manual.

You can bake the mic/cab IR along with the amp info into the TMA; using a cab/IR may yield interesting results, but I think of the TMA block in this case a 'self contained' package; no cab/mic IR required. This is method two in the manual.

I have presets using each method; they are so close it's kinda freaky.

You can also export the combined TMA/CAB match to a cabinet IR slot and use it in a CAB block; no TMA block required (it's the CAB version of the self contained TMA block with the baked in mic)....whew I think that's got it covered :shock
 
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