IR Properties

Discussion in 'Digital & Modeling Gear' started by Jay Mitchell, May 17, 2019.

  1. aleclee

    aleclee TGP Tech Wrangler Staff Member

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    Not questioning whether a reflection-free NF IR would be different. More a question of why it would be more desirable than one captured using typical recording techniques.
     
  2. Jay Mitchell

    Jay Mitchell Member

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    Again, "desirable" is always subjective. If you like the sound of the speaker represented by the green curve above, odds are that you'll like the sound represented in the red curve somewhat less, if at all. It will be both muddier and harsher. Additionally, it can't be equalized to recover the IR represented by the green curve.
     
    Last edited: Jun 17, 2019
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  3. Jay Mitchell

    Jay Mitchell Member

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    Again, you give away your dishonesty. The people who actually got my IRs will know how you have made that obvious....
     
  4. gigsup

    gigsup Supporting Member

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    That was exactly what I did.

    Here's the measurement process I followed:
    • Hooked up my Focusrite via Thunderbolt and used REW to generate a calibration file from the unit.
    • Saved calibration file, closed the REW program and reopened again to be sure the cal file was loaded properly.
    • Applied calibration file to subsequent measurements.
    • In the Kemper, disabled everything I could possibly turn off with the exception of the Cabinet in the Stack section.
    • Swept the Kemper in the loop of the Focusrite, using the Stack output as the return point for measurements.

    Attached is the image from REW, comparing the original IR sweep I made of a DRRI (in Blue), vs. the IR taken from the Kemper (.kipr) directly off of the Cabinet block (in Red). The Green is a sweep of the Kemper with the Cabinet block off, just to see it.



    My inexperience with the REW program is probably in evidence here, I was not expecting the graph of the response to come off the Kemper looking so "smoothed", but as I said in an earlier post, that response curve is consistent no matter where I took the measurement from downstream in the unit. I need assistance with that.

    Testing aside, my opinion is the far field IR's played through the Kemper sound excellent.

    Of course, there are adjustment to be made between monitoring situations. It seems that the slightest adjustments deliver big returns... but I have not compared with other units.
    The thing I find the most compelling with the FF IR's so far is being able to change between bridge, middle, and neck pickups without getting that "unreal" low end bump in response from the neck pickup.

    If you want 10 .wav files of a Marshall 4x12 cab I made to compare things, I posted them here:
    https://www.thegearpage.net/board/index.php?threads/wav-irs-of-marshall-4x10-1960a.2055166/
    Naturally, don't reply to me here about them...;)
     
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  5. AZG

    AZG Supporting Member

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    Spent some more time with Jay's 1x12 and 4x12 far field IR. Still think the 1x12 (C) is great. Finding the 4x12 really hard to dial in.

    Taking the Plexi Bright on the Helix, putting most everything at 5 and adding some supposedly similar 4x12 greenback IR from OH and a couple others I have and I have pretty good tone with some minor adjustments. Doing the same thing with FF greenback 4x12 is really dark, nasal, not great. Spent a lot of time trying get a tone as good as the OH IR patch. Never got anything I like as much. Maybe I would not like this cab and speakers in real life? Somewhat surprised how easy I found the FF 1x12 to dial in something great, but find the FF 4x12 the polar opposite.
     
  6. NPP

    NPP Member

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    I had similar experiences - definitely harder to dial in than the 1x12. Try putting everything on 10 with the Plexi, or playing with the presence control. Or give the JTM45 a go - it works with the 1x12, but I also found it nicer than the Plexi with the 4x12. The Hiwatt gave good results as well.

    Unfortunately I was away for a week and couldn't play around with the 4x12 any more but I hope to get back to it soon.
     
  7. antcarrier

    antcarrier Member

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    I finally got some free time to audition Jay's 4x12. My first impression was: is this a 4x12 with greenbacks? I have a 4x12 with greenbacks that I haven't used for a while, and this IR instantly reminded me of playing that cab. Reading more of this thread -> turns out that a greenback 4x12 is exactly what it is. Unfortunately I won't have a chance to A/B the IR to the real cab for a while, as it is not at my home currently. However, the playing experience was similar to what I recall from that cab (albiet a different brand cabinet). I'd say that the goal of reproducing the direct sound of the cab from a typical playing distance was achieved.
     
    Last edited: Jun 18, 2019
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  8. Jay Mitchell

    Jay Mitchell Member

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    One of the reasons I adopted the practice of sharing IRs along with presets I had built them into is that it removed lots of unknowns from the equation. In the early days of the first-gen Axe-Fx, I often had to use additional signal blocks and alter many advanced parameters to get the amp block to sound convincing. As time went on and FW was updated, the extra blocks became less necessary, and I could leave advanced parameters closer to their defaults. The most recent Amplifire FW has made similar progress toward realism. Not owning a Helix, I have no idea how its amp models behave. A clip of a Deluxe Reverb model in the Helix that was posted earlier in this thread sounded nothing like any Deluxe I've ever played, but that kind of result is possible with any modeler.
    The sound of the 4x12 IR played through one of my monitors is an excellent match for the cab it came from. I went through the exercise of A/B comparisons on several occasions during the refinement process. As you can hear from the two clips I've shared here that use the IR, it is neither muddy nor dark. It is, however, quite different from any close-mic'ed IR of a 4x12. If you've dialed a preset for an IR like that, you're going to need to start from scratch with this IR. Beyond that, I can't offer any advice for modelers I have no experience using.
     
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  9. cliffc8488

    cliffc8488 Member

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    Ah, it wasn't clear that you had turned off the amp and eq. The shorter the IR the smoother it will look. The kemper, as with any modeler, will shorten the IR to its native length. The native length of the kemper is 256 samples. This is a frequency resolution of about 170 Hz.
     
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  10. ipm

    ipm Supporting Member

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    Wouod it be too much to ask you to share your current Amplifire presets with 1x12 and 4x12 cabs you use?


     
  11. AZG

    AZG Supporting Member

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    Jay,

    I would like to say thank you for sharing your knowledge and FF IR with us and that my comments were not meant to be critical. It's been an interesting experience to compare FF IR to some of my favorite close miked IR. It was surprising to me how easy I found FF 1x12 to work with. I literally picked a number of different amps in the Helix, set most everything at noon, and instantly found tone I thought sounded very good. Generally, small adjustments from noon was all I needed to usually get great tones. It's one of the easiest to use IR I've played. Conversely, doing the same thing with the FF 4x12 did not give me the same results. I tried a number of Helix amp models that I thought should be a pretty good match, set stuff to noon, and did not bond with the tone. The JTM 45 model was one of the best natural fits I tried. Most of the models required big presence and BMT adjustments to start sounding better. Makes me wonder if I would dislike the cab if playing it in person? I've played Marshall's in to a greenback 4x12 in the past and found them pretty easy to get a sound I liked. But of course there are a lot of unknown factors when trying to compare a past experience with this IR. Long story short, the biggest shock to me was finding one instantly great, and the other not so much. I will spend some more time messing with the 4x12 IR, but I'm thinking I will need to put an EQ after the IR to get tone that works for me.

    Thanks again for the opportunity to experiment with this stuff.

    David.
     
  12. Jay Mitchell

    Jay Mitchell Member

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    I've played a wide variety of amps over the past 52 years, and I've never come close to getting a good sound with the controls of any of them at their midpoints. I can't say for certain where that notion originated - possibly with boost/cut graphic equalizer faders, which have no correlation with guitar amp tonestacks - but I've never known a guitarist who played a tube amp with bass, mid, treble, presence, at 5. With guitar tonestacks, those settings always create a scooped response which is exaggerated further by amp/speaker impedance interactions.

    IME that is not the best way to evaluate an IR. With a Marshall or Fender amp model, I'd start with bass, treble, and presence at zero and listen to the effect the midrange control has by itself. The frequency band covered by the mid control in a guitar amp tonestack is quite broad and includes both treble and bass ranges. In a Marshall tonestack, diming the mid with bass and treble at zero produces a response that is close to flat, with a very gentle low cut that is down 3dB at 70Hz. After setting mids, I'd bring up treble and/or bass as required to get the sound I wanted. Presence operates differently from the others and will affect both linear and nonlinear power amp behavior at higher frequencies.

    See above. There's absolutely nothing wrong with making major deviations from midpoint in any of the controls.
     
    Last edited: Jun 18, 2019
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  13. AZG

    AZG Supporting Member

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    Thanks for the pointers. I’ve always understood, without good evidence, that setting most controls to noon is a good starting point. Usually works IME as a usable starting point, but could also explain why I’ve not bonded with some real life amps. I will give your suggestions a try in the next day or two.
     
  14. Fireproof

    Fireproof Supporting Member

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    Wow - I can’t wait to try this approach and see if it brings me to better amp tones quicker. I tend to start with all in the middle, like mentioned above.
     
  15. cliffc8488

    cliffc8488 Member

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    Setting bass and treble to zero on a passive tone stack tells you nothing about the response of the midrange control. On a Fender setting bass and treble to zero turns the midrange into a volume control. On a Marshall it turns it into some weird highshelf/lowpass thingy.

    A passive tonestack is a very different animal than active tone controls with well-behaved frequencies.

    Download and play with Duncan's TSC to see the effects.
     
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  16. hippietim

    hippietim Member

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    Interesting...I'm curious now. Does the Axe III respond that way too?
     
  17. cliffc8488

    cliffc8488 Member

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    Of course.
     
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  18. hippietim

    hippietim Member

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    :dude
     
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  19. Chocol8

    Chocol8 Member

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    I start with the controls wherever they are at and then try to add what I think it lacks or subtract what I think it has too much of. It is usually an iterative process since the controls are interactive/overlapping on most amps.

    I do tend to set gain and volume level first and then revisit if the other controls (mids?) have an impact. I also turn the guitar volume down a bit (7-8 depending) and set there. Then I can turn up or down (add gain or clean up) from the guitar.

    As for Jay’s 4x12 being dark or not, I think that is driven by what you came from. Take a glass of room temperature tea. If you have been drinking iced tea, and take a sip, the room temp glass would seem warm. If you drink hot tea first, you would likely describe the room temp glass as cold. It really is neither.

    Compared to common greenback 4x12 IR’s, Jay’s IR has less high end and you should twist some knobs before deciding if it is dark and muddy. It definitely is not, but I do agree that it took me more time to find a setting for it that the 1x12 “c” which sounded good with my Fender clean presets as they were already set, simply by removing the high and low cuts.
     
  20. djd100

    djd100 Member

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    For those who'd like to visualize what Jay is talking about, see here...

    https://www.guitarscience.net/tsc/marshall.htm

    A downloadable Windoz version is here...

    http://www.duncanamps.com/tsc/
     

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