Why is De-Phase necessary?

From what I gather, this is a digital solution to an issue akin to JH Audio's physical solution (FreqPhase) to a similar issue with cramming tiny armatures into a reeallly small space right next to your ear. Phase cancellation is the devil.
 
Close mic a cab with a dynamic mic (SM57, etc.) and you're capturing a 1" or so piece of a 12" speaker. Therefore sound waves from all parts of the speaker are reaching the mic capsule at different times, causing phase cancellation. From what i understand, the de-phase control helps to correct that.

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USMC_Trev said:
Yeah you are correct. Doppler shift is frequency change due to movement of the source.

What's the term for the phenomenon caused by change in position of the observer...?
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Spatial Variability. That's the vibroacoustic term at least for the difference in measurements between several pressure transducers or accelerometers. Sound engineers may call it something else. Coherence is the the measurement of how in phase different locations are to the same wave among other things.
 
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steadystate said:
It might be the single most important parameter for me in the Axe.
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Playing with Dephase last night for only a couple of hours it's looking like it's going to be an extremely important parameter for me as well; I always enthuse dramatically about firmware and new parameters that excite me and Dephase is a game changer for me with regards to the AFX and IR's.

As much as I may like recorded tones, 99.999999% of the time I'm not listening to myself play with my ear right up to the speaker either (yes, a great comment!) and am extremely curious to try my other near field IR's (I've also got a huge collection of near field IR's, most of them I never could bond with either) to see if I can bring them to life now.

I never liked the sucked out, phasey sound of many near fields I've tried over the years and it's exciting to think they may be useful to me finally.
 
FractalAudio said:
You don't listen to a guitar speaker with your ear against the grill cloth.
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But, isn't it pretty fair to say that most of the greatest guitar tones were recorded this way. I have certainly recorded guitar with an sm57 right in front of a cab and gotten a great recorded tone; and the essential recorded tone sounded pretty much the same as the amp in the room. So it would seem that the sound being generated at that point is an acceptable sound.

I certainly have not studied this technology, and I am quite satisfied with the axefx and the stock ir's. I only use a few and I do feel that a real cab is still a little better than frfr. But, I would imagine that a true frequency response from a speaker, whether in a cab or not, would yield a fairly smooth response. I would imagine that the jagged response seen on the mic input of most ir's is due to other frequency anomalies interfering with the true response. Just like a response taken from a room where you have frequencies bouncing all over the place. I know that the sample time is very short for a speaker ir, and that would start smoothing out the lower frequencies. However, I suspect that the ir time is not sufficiently short to prevent interference in the upper range. I suggest dephase is a process to overcome this type of interference. If the interference is included in the ir, you have essentially double the effect. Sort of like using an ir with a real cab, or power amp sim. with a tube power section. Dephase is a better way to lesson this effect than using a standard hi cut filter, which would also smooth the peaks out. I could also be stoned right now.
 
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markiv said:
Yeah, can someone advise what should be the ideal setting (0 to 10) be like for this cool feature? Really curious how are the other Axe users dialling it in. Thanks....
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It's totally up to the user to decide. It smoothes the peaks and valleys in the IR, too smooth loses its character, but a little bit improves clarity. So, tweak to taste. The "phase" word is perhaps a bit misleading since it doesn't affect phase in that "in-out/0-180'" way at all.
 
markiv said:
Yeah, can someone advise what should be the ideal setting (0 to 10) be like for this cool feature? Really curious how are the other Axe users dialling it in. Thanks....
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there isn't "ideal". I've used values as low as 0.5 up to high as 6. on some IRs I don't use it at all. depends on how the original IR sounds and what tone you're after...
 
guitarmike said:
But, isn't it pretty fair to say that most of the greatest guitar tones were recorded this way. I have certainly recorded guitar with an sm57 right in front of a cab and gotten a great recorded tone; and the essential recorded tone sounded pretty much the same as the amp in the room. So it would seem that the sound being generated at that point is an acceptable sound.
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Yes, many great recorded tones were made this way. And those great recorded tones were because the engineer and producer spent hours getting the mics in just the right position, testing and adjusting over and over. Unfortunately the vast majority of IRs were not produced with this level of precision because the financial incentive isn't there (I could wax on about quality over quantity in this regard and the unfortunate trend in the industry to offer quantity rather than quality).

De-Phase allows you to remove those unacceptable characteristics of IRs that were captured with less than optimal mic placement.
 
So the basic question is, how does the value on the led correspond to the function? You have a scale of 1-10 so....? Also does de phase require multiple IR's in use as a function of adjusting phase of one opposed to another?

I feel like I can tell the difference with one IR but I've fooled myself into believe in things that weren't there before.

Thanks in advance for any replies...
 
dbun said:
If an IR is simply a capture of a cab mic'd up, what is going 'wrong' with the process that De-Phase becomes necessary?
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Good question. The answer has to do with the imperfections that arise when you close-mic a speaker...


Rex said:
The De-phase parameter corrects for the phase issues that occur whenever you close-mic a speaker cab, even if you're only using one mic.

Remember that a guitar speaker is essentially a chunk of hardware twelve inches across. Each point on the speaker generates sound. When your mic is close to the grill, sound from the speaker is coming at it from straight in front of the mic, from parts of the cone above the mic and below the mic, from the right and left sides...

All these parts of the speaker are at different distances from the mic. So the sound from each part arrives at the mic at different times, and that means they're out of phase with each other. The De-phase parameter reduces that out-of-phasiness and smooths out the response, making it sound more like your cab sounds when you're listening at a reasonable distance.
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