IR Properties

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

  1. Jay Mitchell

    Jay Mitchell Member

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    It makes more sense than it sounds like at first.

    Pro - for any given IR length, it saves cpu horsepower.
    Con - when used as L6 is apparently using it here, it can run the risk of obscuring some details of the sonic signature of a cab.

    Not definitively. The reduced rate of decay from ca. 3ms onward - and the peaks that follow - could be due to early reflections.
     
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  2. AlbertA

    AlbertA Member

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    I find it easier to compare MPT vs non-MPTed by looking at the group delay instead. For example, for Jay's FF IR (the offset in the graphs is not artificial):

    [​IMG]
     
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  3. Mark Al

    Mark Al Member

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    I get that now, thanks :)

    That makes sense, that seem to echo how Helix "optimize" its DSP usage.

    I guess that's true, theoretically. Not sure why my ears almost always prefer Helix stock cabs if dialed in right, when comparing to various commercial IRs...

    Right, it's inconclusive. To my ears though, Helix cabs do sound like containing minimum amount of reflections, compared to almost all other commercial IRs. Also Helix stock cab has a dedicated "Early Reflection" setting that allows users to add appropriate amount of reflection back, which is a neat feature.

    Thanks a lot Jay, for plotting the Helix cab :)
     
  4. AlbertA

    AlbertA Member

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    This was mentioned earlier in the thread. You still need a substantial sized room just as you would need to capture a reflection-free far-field using the ground plane measurement technique. The added requirement is that now you also have to avoid the ground reflection - because now you are close mic'ing, the mic itself is elevated to be positioned at some point in the cone. In order to avoid this reflection, you can elevate the cabinet in question from the floor enough to avoid getting the reflection in the area of interest i.e. around 20ms, which comes to around 12ft of elevation (see IR Properties) - the same goes for the reflection from the ceiling.
     
  5. cliffc8488

    cliffc8488 Member

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    The offset is nearly constant which is simply the fixed delay. If you were to delay the MPT version by some number of samples that offset would be removed. IOW a fixed delay contributes equal group delay at all frequencies.

    Aside from that they look almost identical. The only substantial difference is in the very high frequencies where there is hardly any energy anyways. 100 Hz to 6 kHz or so is the usable range and over that range they are nearly identical.
     
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  6. vtgearhead

    vtgearhead Silver Supporting Member

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    I've done a bit of listening to Jay's IR samples and will risk making a fool of myself in public by offering my guess as to which is which.

    (A) Jay's near-field IR
    (B) Brand X "far-field" IR
    (C) Jay's far-field IR

    Now to wait and see whether I'll need to be wearing a paper bag over my head for the next day or two.
     
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  7. Mark Al

    Mark Al Member

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    Ah man, you ruined the fun for other folks who is going to try these IRs.... Jay's far-field IR is quite impressive, isn't it? I imagine it could be even better if done with other cabs and mics... :)
     
  8. vtgearhead

    vtgearhead Silver Supporting Member

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    If I was in the position to make an authoritative statement, _that_ would be a spoiler. However, I was hopefully clear about my post being an educated (or maybe not-so-educated) guess :).
     
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  9. GravityWell

    GravityWell Member

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    I think I concur here. B is unusable for me, I knew that instantly. A and C are quite remarkable. I need to experiment some more, but they could easily replace anything I currently use.
     
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  10. Mark Al

    Mark Al Member

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    I don't think it could replace everything I use, which is not the point of this demo. It's just a single FF IR for a specific open cab...

    The point, for me at least, is hearing the drastic different/better tonal characteristic of FF IR than the typical NF IR demonstrated the great potential for FF IRs, and It convinced me that, if done right, they are potentially capable of delivering a much more natural tones than NF IRs. We definitely need more of them :)
     
  11. AlbertA

    AlbertA Member

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    That's almost correct, but it's not entirely fixed over all frequencies. See the following, where I've manually trimmed the IR. It mostly aligns around the 2-3KHz region.

    [​IMG]

    Yep. Though that's not entirely the case here, close but not quite.

    Over the years I've always maintained that the MPT transform is audible but subtly so and that IRs seem to approach minimum phase on the low end diverging on the high end. From the chart above, you can see at least for this IR, the region from 3-5KHz still contains enough energy to be significant (-10 to -20dB is definitely in the subtle area) - at the same time, the group delay started to diverge from 3KHz on - maybe that accounts for the subtle difference I hear.
     
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  12. cliffc8488

    cliffc8488 Member

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    Manually trimming is not the correct way to compare. You need to add zeros to beginning of the MPT version. If you trim you'll remove energy content.

    Regardless, MPT sounds almost identical and for the average user solves a raft of usability issues.

    Non-MPT is something only advanced users should consider.
     
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  13. yeky83

    yeky83 Member

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    @AlbertA What's the scale of the y-axis on your group delay graphs? :bonk
     
  14. AlbertA

    AlbertA Member

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    I Only trimmed the zeros so no energy lost. But you are correct, to properly align the peaks I should delay the MPT version instead. Here's the result, so yes mostly no difference from 100 to around 3KHz - but like I said before that 3-5.5/6KHz region is probably the subtle difference I detect.

    [​IMG]
     
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  15. Jay Mitchell

    Jay Mitchell Member

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    Or argue ceaselessy with the facts that are being pointed out. :p
     
  16. AlbertA

    AlbertA Member

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    In the first 2 graphs, it's in units of samples. The last chart I converted to milliseconds.
     
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  17. Jay Mitchell

    Jay Mitchell Member

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    Close-mic'ed recorded tracks pretty much have that floor reflection baked in. I don't consider that a positive, just an inevitable tradeoff. The real reason for close-mic'ing - minimizing bleed from other mics - caused the tradeoff, but my money says that most recording mixers didn't recognize that it was even there. The resulting guitar tones were the result of not just the mic'ing technique (sorry to bust a myth) but of the sound the mic picked up plus all sorts of other games the studio guys played with it, including equalization, compression/limiting, adding reverb, etc.
     
  18. Jay Mitchell

    Jay Mitchell Member

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    We are professionals. Don't try this at home. :D
     
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  19. Chocol8

    Chocol8 Member

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    Years ago when people were chasing a certain album tone, the answer was all you need is X guitar, Y amp and 7 figures worth of studio gear. These days the average guitarist can do all that with a laptop and a couple hundred bucks worth of software. Well, that and a little knowledge, skill, and experience using those tools. But, for those inclined to such pursuits, I think it is more achievable than ever.

    I am more interested in getting a modeler into an FRFR to sound closer to my real amps and cabs. For that, I think your far field ground plane IR technique recorded off my actual cabs might be the ticket. At least I would like to think that until I fail miserably and come crawling back for more educating.
     
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  20. GravityWell

    GravityWell Member

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    Correct, it is not the point of this demo. I meant to infer that I could easily see it replacing the IRs I currently use that are Deluxe Reverb IRs.
     

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