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Real Mesa Dual Rectifier vs Axe-Fx III and input impedance woes...

Discussion in 'Axe-Fx III Recordings' started by ML SOUND LAB, Oct 27, 2018.

  1. #1 ML SOUND LAB, Oct 27, 2018
    Last edited: Oct 29, 2018
    ML SOUND LAB

    ML SOUND LAB
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    SOLUTION FOUND: Get a proper loadbox. Two Notes Captor was used here and it was causing all the problems!

    Okay so I've been geeking out at the studio lately and I ran into a problem that is huge to someone like me. You may or may not know this but when you plug your guitar into a real amp there's some impedance magic happening that essentially loads down your pickups meaning that it sounds completely different if you have anything inbetween. So my problem is that having the Axe-Fx III inbetween my real amp signal chain changes the sound of my Dual Recto completely. Here's a clip:



    1. Guitar straight into the Mesa Dual Rectifier with all knobs on noon. Red channel, modern.
    2. Running the signal through the Axe-Fx III
    3. Trying to volume match that signal
    4. Axe-Fx III Dual Recto amp sim with default settings
    5. Axe-Fx III Dual Recto amp sim with master setting at 5 just like on the real amp.

    So there is a happy ending. The Axe-Fx III amp model sounds pretty much identical to my real Recto if they have the same settings. This is awesome! But the thing is... I love the sound of my guitar plugged straight into the amp and I also love that the Axe-Fx III sounds just like that. I'm just wondering if there is a way for me to get that same sound by running the signal through the Axe-Fx III.

    I even tried using a DI in front so that I split the signal to my real amp and the Axe-Fx III but once I plug the Axe-Fx III into the DI box it also changes the sound of the DI signal going to the amp.

    Help! Opinions?
     
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  2. bradlake

    bradlake
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    Do you have the same result if you use Output 2 to your real Recto and in I/O you are set to Echo Input 1?
     
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  3. ML SOUND LAB

    ML SOUND LAB
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    Yes I tried that as well. Having anything digital or even some pedals in front of the amp would change the sound quite drastically. The DI test that I did was the turning point for me. If I plugged my guitar to the DI and the DI through to the amp I was still getting the amp input impedance pull but if I plugged anything else to the DI and in this case the Axe-Fx, it changes things and changes the sound even though the DI through is going to the amp.
     
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  4. Raab90

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    It's not like amplifiers have some impedance magic. Actually, they have very high input impedances (a very big resistance to ground) to be able to work with a strong input signal. Remember they work with input voltages. This is why unlike fuzzes, amps don't interact with your pickups when you lower your volume.

    For the same reason, the AXE FX also has an input buffer, and therefore a very high input impedance.
    This means that adding the axe fx to the signal chain means adding another big, non-negligible load onto the pickup.

    This effectively increases the total resistance on the circuit and shifts the cut-off frequency of the input circuit to the right. I haven't listened to your clip but I'm pretty sure adding the AXE FX makes both sound darker.

    If you run them both on parallel it should sound brighter.
     
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  5. Bryanman37

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    I had this same issue with my JP2C and posted a thread about it. I was running 4CM to utilize drives, etc from the AX3 into the front of the amp and delays, etc post cab (the amp runs into a Two Notes live). I found that using this method substantially changed the tone but if I used the AX3 only in post I had no issues.

    I’ll be interested to see where this thread goes as I have not gotten this sorted. However, the AX3 sounds so good I haven’t used the JP2C much lately.

    The comments about impedence at the input makes sense- I definately found the tone darker/warmer with the AX3 in 4CM.
     
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  6. ML SOUND LAB

    ML SOUND LAB
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    If I compare the signal with my guitar straight to the amp vs having something like the Axe-Fx III in between, I get a much darker guitar tone. Even after the amount of gain that I have in this clip f.ex. I still have around 3-5dB less high end.

    Also another thing to point out is that I had to volume balance these clips. When running the signal through the Axe-Fx III there's a huge volume boost.
     
  7. yek

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    Check Output Level in I/O > Audio. Is it set to +4dB?

    For simple unity gain, connect to I/O 3 or 4. Just make sure to turn up the output knob at the front all the way.
     
  8. ML SOUND LAB

    ML SOUND LAB
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    Both things checked and tried various settings. I tried many things this week to try and solve this. Same thing happens if I plug my guitar into my USB interface and run that signal to the real amp. There's a Kemper in the studio right now so a Kemper buddy already gave me "that smile" and said the Kemper has an analog Direct out. So...... I tried it and even that so called "analog direct out" has this same problem.

    I've been reading about reamp boxes that supposedly lower your signal impedance back to normal... has anyone tried these out? If they work I think I need to buy one of those. Truth be told I definitely need to find an A/B clip proving that it works.
     
  9. OldSnail

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    Just an non-educated suggestion: have you tried to play with « impedance » value in the IN 1 block ?
     
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  10. ML SOUND LAB

    ML SOUND LAB
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    Yes and it works really well. It's just not the solution for my problem unless the Axe-Fx is capable of putting out the impedance of my real guitar. Is it? This is essentially what I'm trying to find out.

    If not, doesn't this mean that live tone matching fails?
     
  11. Raab90

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    Not really, because what’s important here is what’s done to the input signal, not the input signal per se.
    So as long as you feed both platforms the same signal, and it stays within the dynamic range of whatever system you’re feeding, there should be no problem.

    Otherwise, using differeny guitars would yield different results when tone matching.

    (Assuming the process it’s linear and time-invariant)
     
  12. FractalAudio

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    I can't reproduce this.

    Some points:
    1. You should use Output 3 into the amp. Outputs 3 and 4 are intended to drive "guitar level" devices.
    2. Cabling will have a considerable effect. The shorter the cable, the less high end loss but... it may not be perceived that way since the capacitance of the cable shifts the resonant frequency of the pickups down which may sound "brighter".

    Here's a comparison of a simulated 10K ohm pickup into 10 ft. of typical guitar cable into the input of a Dual Rectifier and then the same pickup and cable into the input of the Axe-Fx iII. The green trace is the Recto, the blue trace is the Axe-Fx III. The Axe-Fx has slightly more high frequency extension and the resonant frequency is slightly higher. The Axe-Fx III input was designed to mimic a typical tube amp input using an average of Marshall and Fender amps for the component values.

    recto_vs_axe_input.JPG
     
  13. FractalAudio

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  14. Raab90

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    Would it be possible to add the cascaded AXE FX into the Recto?
     
  15. FractalAudio

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    I have no idea what this means.
     
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  16. Raab90

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    Try the following.


    You, currently have 3 recordings right?


    a) Real amp through guitar->recto (brighter)

    b) Real amp through guitar->axe->recto (darker)

    c) Tone matched model through guitar->axe->recto (darker)


    Now plug the guitar straight into the axe and do a record with your tone matched recto model. It should sound brighter now.

    That test is

    Pickup->Axe
    Pickup->Amp

    But I’m wondering if you could do a Pickup->Axe->Amp test and add it there on that Bode plot
     
  17. ML SOUND LAB

    ML SOUND LAB
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    I hope to find a solution and wish and sincerely hope that I'm doing something wrong. This is not only about the Axe-Fx, like the test that I did with the DI box: guitar into passive DI with input through going to the amp in sounds completely normal, plug an XLR from the DI to anything and it changes the sound. If the sound difference was small I wouldn't care but it's really big right now. Here's a pic of the waveform difference:

    [​IMG]

    Here's an audio clip:

    https://www.dropbox.com/s/ciosr430mzmyxp7/Problem.wav?dl=0

    And this happens on both my Mark V and Dual Rectifier.
     
  18. FractalAudio

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    Still no idea what you're saying. How do you put a "real amp through guitar"?

    One clip is guitar->Axe-Fx->Ouput 3 to amp.
    Another clip is straight into the amp.
    The third clip is one or the other to keep you guessing.
     
  19. FractalAudio

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    You can't use a DI box. It will load down your pickups dramatically as soon as you plug a cable into the XLR jack.
     
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  20. FractalAudio

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    And what I'm saying is that they do sound the same and there are clips to prove it.
     
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