Axe-Fx II Technical Questions Thread

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LMO said:
Merlin17 did something like this for his Verve, but I don't think he was thrilled with the results. Since guitar speakers are so directional it's only going to work very close to the mic position used in creating the IR.

Why not try inverting an IR and see if you like the results?
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Inverting an impulse response is not the same as applying an inverse response. In other words, simply flipping the phase does not do it.

You have to do an inverse calculation on the impulse to get the inverse response.

I could do it 'offline' and then upload it, but it would be so much more convenience to simply hit a button than to do all of that work each time you want to inverse an IR.

L
 
LMO said:
Merlin17 did something like this for his Verve, but I don't think he was thrilled with the results.
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I use Merlin's IR to flatten the Verve and I'm very happy with the results. My Verve and my studio monitors are much closer now. And the tone coming out of my Verve sounds very close to what I'm hearing out of FOH.
 
What you're trying to accomplish is a cool idea but this will not give you a flat response speaker cabinet, if I understand this correctly inverting the response would just give you noise wouldn't it? It would not produce the effect of a flat response cabinet. I don't know much about this stuff but that was my understanding.
 
jdolll said:
What you're trying to accomplish is a cool idea but this will not give you a flat response speaker cabinet, if I understand this correctly inverting the response would just give you noise wouldn't it? It would not produce the effect of a flat response cabinet. I don't know much about this stuff but that was my understanding.
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You are correct, it would not be a perfectly 'flat' response... but it would be a baseline to add a replacement response.

And no, it would not simply add noise.

You can think of Impulse Responses in their simplest form as just steep EQ curves. (I know that's not EXACTLY what they are, but you get the idea)

So if your real cabinet is a Marshall 1960a but you want to have a EQ curve of a 4X10 Bassman, you would first have to take the 'Marshall 1960a' response back to some sort of baseline (i.e. as flat of a response as possible) and then add the 4X10 Bassman to replace it.

Of course, it would not sound EXACTLY like a 4X10 bassman because it is an open back cabinet and the Marshall 1960a is a closed back cabinet, but you could get the EQ curve - which is what I'm wanting to do (among other things).

Convolution (which is what Impulse Responses are) is the way of the future.

And I'm so glad that Cliff took this approach in doing the AXE-FX II. With convolution, you can get some incredibly great sounding emulations.

Of course, a single impulse response taken at one 'level' will not work for all 'levels' because as you crank up the gain to the speaker cabinet, there is some non-linearity going on.

But as I understand it, the new AXE-FX II has multi-sampled IR's (which is WAY COOL!)

If Cliff was able to do this without 'zipper' noise (i.e. switching from one IR to another IR dynamically) this is a major accomplishment.

And if this is true, then I don't see anything coming close to what this unit does anytime soon (not counting plugins on fast computers - but who wants to gig with that?)

All the best to you!

Larry
 
larryseyer said:
You are correct, it would not be a perfectly 'flat' response... but it would be a baseline to add a replacement response.
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When you equalize a loudspeaker to flatten its response, if you do the job correctly, the equalizer's IR is an approximate inverse (in the frequency domain) of the IR of the unequalized loudspeaker. Convolved with each other, the two IRs result in an idealized IR.

Convolution (which is what Impulse Responses are)
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Convolution is what DSP-based systems do with impulse responses.

But as I understand it, the new AXE-FX II has multi-sampled IR's
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It does not.
 
Jay Mitchell said:
When you equalize a loudspeaker to flatten its response, if you do the job correctly, the equalizer's IR is an approximate inverse (in the frequency domain) of the IR of the unequalized loudspeaker. Convolved with each other, the two IRs result in an idealized IR.

Convolution is what DSP-based systems do with impulse responses.
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Correct. I didn't take the time to word that properly. But you are correct.

But as I understand it, the new AXE-FX II has multi-sampled IR's

It does not.
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Ok. I had thought I read somewhere that it did.

If it did, that would be very impressive. But even since it doesn't, the unit still has my attention and I'm gonna get one.

Any ideas if an 'Inverse Impulse Response' button will be added?

L
 
larryseyer said:
Any ideas if an 'Inverse Impulse Response' button will be added?
L
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Maybe I am missing something, but could you not compute the inverse IR in software, and upload that inverted IR in one of the User Cab locations in the AxeFx? Since there are two Cab blocks in the Axe, nothing stops you from placing them in sequence, where you put your inverse IR in one, and the desired Cab IR in the other.
 
Arjan said:
Maybe I am missing something, but could you not compute the inverse IR in software, and upload that inverted IR in one of the User Cab locations in the AxeFx? Since there are two Cab blocks in the Axe, nothing stops you from placing them in sequence, where you put your inverse IR in one, and the desired Cab IR in the other.
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Absolutely!

But it's a heck of a lot easier to hit a button than to go through that process!

And besides, behind able to un-cab things with a touch of a button is a much quicker way to find new sounds than futzing with a computer.

One of the big advantages of using the AXE-FX over a computer is it's dedicated function and ease of use.

Sure, I can do this using computers and software and uploads - but that's not what the AXE-FX is about IMHO. At least that's not what it is for me.

Which is why I had asked if we could have a reverse Impulse Response button.

Supposedly Cliff has the code already written, but it's commented out (for whatever reason).

L
 
Okay. I'd have to disagree with you on the merits of adding such a button though. For one, you already went through the trouble of capturing the IR of your specific cab. Exporting the inverted IR from the software instead of the `regular' one doesn't seem like a lot of extra work to me. Furthermore, this is probably a process that you will do only once (for your specific cab). Finally, adding such a rarely-used button to the UI in the AxeFx will IMHO clutter up the simple interface that is there now, making it less evident for the users.
 
larryseyer said:
Inverting an impulse response is not the same as applying an inverse response. In other words, simply flipping the phase does not do it.

You have to do an inverse calculation on the impulse to get the inverse response.

I could do it 'offline' and then upload it, but it would be so much more convenience to simply hit a button than to do all of that work each time you want to inverse an IR.

L
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Applying an inverse IR to flatten a cab response would only work for one position , where the measurement mic is. You then would have to not move your head from that position in order for that inverse IR to work. That is assuming that cab is linear and the system is not time variant.

In other words if anyone managed to accomplish this they would have a product worth at least 10000$ in hifi circles
 
larryseyer said:
Inverting an impulse response is not the same as applying an inverse response. In other words, simply flipping the phase does not do it.
Click to expand...
invert verb |inˈvərt |
put upside down or in the opposite position, order, or arrangement:

inverse |ˈinvərs, inˈvərs| adjective
opposite or contrary in position, direction, order, or effect:

I was just trying for a verb that means to create the inverse, but I guess in this context it was a poor choice.
 
drosei said:
Applying an inverse IR to flatten a cab response would only work for one position , where the measurement mic is. You then would have to not move your head from that position in order for that inverse IR to work. That is assuming that cab is linear and the system is not time variant.

In other words if anyone managed to accomplish this they would have a product worth at least 10000$ in hifi circles
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I believe are confusing inverting the response of a cabinet which is indeed mostly a linear system, to equalizing acoustics in a room. The first is doable (with caveats such as dealing with nulls in original response, noise floor, etc) the latter is essentially impossible.
 
Sorry if this is a simple question (or has already been answered) but I don't have the time to wade through 144 pages.

Is it possible to insert my classical guitar (featuring an active piezo system) into the Axe2, bypass the amp and preamp section and just use the FX (like verb or delay) with good results?
 
monty said:
Sorry if this is a simple question (or has already been answered) but I don't have the time to wade through 144 pages.

Is it possible to insert my classical guitar (featuring an active piezo system) into the Axe2, bypass the amp and preamp section and just use the FX (like verb or delay) with good results?
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Yes. This is possible with the Standard/Ultra currently as well.
 
I have a question I'm surprised I didn't think of before.

Will I be able to use the MIDI ports on the Axe-Fx II to edit patches on the Axe-Fx Ultra with Axe-Edit?
 
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