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Non-Minimum Phase IRs

Discussion in 'Axe-Fx III Discussion' started by FractalAudio, Jan 3, 2019.

  1. ben ifin

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    ^^^ Thanks.
     
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  2. flying_walrus

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    every waveform has a phase. MP IRs are artificially aligned to an arbitrary standard, therefore they're all theoretically aligned to each other.

    if you're using a single "raw" IR you won't have phase alignment issues, but if you use 2 of them you may need to pay attention to the alignment.
     
  3. #23 brianv4, Jan 3, 2019
    Last edited: Jan 3, 2019
    brianv4

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    I like the way these NON-MP IR's mix in the cab block. Adjusting the level control of cab 2 (f ex), you really hear a more dramatic tonal change whereas with MP IR's I always just kept the mix the same (0dB). IOW, mixing multiple NON-MP IR's in the cab block is more noticeable.

    I just tried the 1959SLP Treble (BMT about 6) with the 4x12 Marshall GB KSM313C at 0dB and the same Marshall IR with the M160A IR at minus -11.87 and my Strat, wow!

    EDIT: @FractalAudio Are these new NON-MP IR's from the Wellspring collection Ultra-Res? The titles aren't italicized, or is that only used in the Legacy bank? Doesn't really matter cause either way I'm really liking them!
     
  4. #24 DLC86, Jan 3, 2019
    Last edited: Jan 3, 2019
    DLC86

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    I'm happy to see I'm not the only one "hearing things", Lol

    I made some experiments with this a few months ago as well and found that:

    1) the attack, as you say, is different, it seems softer with non-MPT IRs

    2) I think it also changes the character of the feedback too.
    Since MPT actually changes group delays, different frequencies would be in phase with the string vibration compared to non-MPT, rhe harmonics emphasized by the feedback will probably be different (assuming the same distance and position of the guitar relative to the speaker obviously).
    EDIT: the same thing also affects how I perceive the sound when playing at low volume, the sound coming from the speakers interferes in a different way with the sound coming directly from the strings and this gives the impression that the tone changes when switching between MPT and raw.

    Anyway a while ago I actually thought of a possible useful feature.
    Would it be possible to have a switch that applies minimum phase directly within the cab block instead of being forced to import them raw and processed? Like it currently is on cab-lab.
     
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  5. #25 Variable, Jan 3, 2019
    Last edited: Jan 3, 2019
    Variable

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    This is such a timely topic given I've been pondering this same thing myself in my own first cab pack. I find that I prefer the non-MPT files I've created over MPT. Not for the sound, as I can make them sound fairly identical, but for the feel (as the man himself mentioned). There is a certain "give" to the non-MPT files. I just did a greenback mix, MPT vs. manually aligned (preserving the initial few milliseconds of the capture) and the manually aligned mix just feels better to me.

    I personally am not a fan of phasey sounds, so I probably won't be doing any of that type of non-MPT fun in this pack, but I certainly will be manually aligning my mixes to help preserve that initial few milliseconds of lag time that I think contributes to the feel.

    That said, this of course all goes back to player preference and the style of music. I think MPT files probably would work better for applications that need a more immediate attack (djent, for example) vs those that do better with more give (like the blues). Providing both I think is the best of both worlds.

    You can always futz with the mic distance parameter in the cab block, which I believe can add some distance delay "virtually" to an MPT file.
     
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  6. 2112

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    I've been playing with that parameter a bit recently and enjoying the results, especially on ribbon captures.

    Quick clip with the Atomica and one of my go to IR's imported as non-MPT (first clip) and MPT (second). The final clip flips between them. It's very subtle. IR's attached if anyone wants more to try.

     

    Attached Files:

  7. peteri

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    Very impressive, coming from a user perspective (rather than a technical engineering standpoint) - I've found these much more intuitive to mix, just feel like I expected more somehow.

    And two of the 4x12s have really helped me get closer to my memory of my 1987 experiences with the Jubilee stack I should never have sold!
     
  8. Tremonti

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    Thanks Cliff!
     
  9. FractalAudio

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    That's just delay. Same thing as moving further away from the speaker (or using a delay block with 100% mix). Minimum vs. non-minimum phase changes the "delay" of the individual frequency components of the waveform. In a minimum phase system the individual sine waves have the least phase possible which concentrates the energy near the start of the waveform.

    For example consider a sine wave with an isosceles triangle envelope. The energy is concentrated at the center of the waveform (at the apex). The Fourier transform of that is mostly the primary frequency with a bunch of other sine waves at various amplitudes added. We can phase shift the component sine waves and the magnitude (frequency response) will not change but the waveform will. If we make it minimum phase the sine waves will add up so that the energy is concentrated at the beginning of the waveform and the waveform will then look something like a sine wave with a right triangle (ramp down) envelope.

    Remember the old Behringer V-Amp. It's IRs were "maximum phase" because they forgot to reverse the data when processing (since convolution is x(t)*h(t-tau)). If you played one the IRs sounded okay but the feel was a little strange. Reversing an IR gives the exact same frequency response but adds latency equivalent to the IR length.
     
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  10. yek

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    I also hope that, some day, Mike from Red Wirez will release UltraRes, non-MP versions of the RW IRs. I use the stock ones (excellent mixes by Cliff) a lot, especially the G12H30. I'd love to know the mix recipe, to apply to other RW libraries.
     
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  11. brianv4

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    I contacted them maybe a year(?) after ultrares was introduced and was told they were working on it. It's been a while, who knows but i somehow doubt it at this point. One can only hope!
     
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  12. brianv4

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    Nice work as usual! Without comparing directly, side by side I'd say the difference is negligible. The real difference seems to be when mixing NON-MP IR's
     
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  13. yek

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    Yes, that was 2014.
     
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  14. 2112

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    I'll do another with some mixes of the IR's Cliff shared and compare them with the stock ones.

    @FractalAudio thanks for the excellent explanation. I remember the old V-Amp too, never tried one though. might have to have a peak on ebay...
     
  15. hedua

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    Gracias Cliff!
     
  16. yek

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    After spending a couple of hours playing and comparing, I can "attest" that the non-MP IRs indeed sound slightly more open and natural.

    Also, they feel better. Compared 1 to 1, the non-MP IR makes playing very slightly easier and relaxed, less effort needed.
     
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  17. rodzimguitar68

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    I hear "a" difference. But, from what ya'll have been saying, it is more apparent in how it feels when you are playing one vs. the other. And, with a reamp track playing the part, obviously, we have only the recording side of the equation, and not the feel, side.

    Thanks for the presets, I will check them out!!

    Edit: Duh, then I read Yek's assessment......
     
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  18. Holyoli

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    Absolutely ! Although I wrote in a previous thread I couldn't hear any difference between MPT and unprocessed there is definitely a very subtle one.
     
  19. yek

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    In the past years I haven't been experimenting with IRs a lot, staying away from the infamous "rabbit hole''. I know what and which I like and stuck to that.

    However, this non-MPT affair made me go through the @ownhammer libraries again, because the libraries released in recent years contain non-MPT files (in the 48kHz 200 ms WAV folder). These can be converted to non-MPT .SYX and .IR files with Cab-Lab.

    Made some nice IR discoveries, in my realm. One of those is that I still like the "SP" mix recipe in the OH libraries a lot, created by @Scott Peterson.
     
  20. Holyoli

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    Now regarding mixing non or MPT ir's, there is something I don't understand :

    - I tried to mix in the cab block some non MPT wellspring irs with various factory (MPT) irs of the axe (from different manufacturers too). I was expecting phase problems but there is not, shoudn't it be the case as I mix an unprocessed file with a processed one ?

    - When mixing a wellspring irs or a factory MPT from the axe with a non MPT Ownhammer irs from my library, there is a phase problem that cannot be solved with the cab block mic distance. The only way to make it work is to the smoothing, in fact using my keyboard CTRL command when moving the smoothing knob makes it work even before I see the 0.01 in the window above the knob ! I can hear the sound changing step by step turning the virtual knob till 0.01 although it still reads 0.00
     

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