IR Present for You

Not to take anything away from the cab packs but I downloaded this IR not expecting too much.

Surprise surprise.....this IR is really nice! The reference compensation is where it's at.
You got my attention. What cabs are you capturing? Are you capturing all the IR's and using the reference compensation feature?

Thanks for free IR Cliff!!

Yes, I think reference compensation is the missing piece of the IR puzzle. IRs are, in theory, extremely accurate. The problem is that your average power amp isn't perfect, especially when driving a complex load. This causes inaccuracies in the frequency response, especially around the resonant frequency.

IR compensation allows you to capture a reference IR of the voltage right at the speaker terminals and then apply the inverse of this to remove the errors.
 
Yes, I think reference compensation is the missing piece of the IR puzzle. IRs are, in theory, extremely accurate. The problem is that your average power amp isn't perfect, especially when driving a complex load. This causes inaccuracies in the frequency response, especially around the resonant frequency.

IR compensation allows you to capture a reference IR of the voltage right at the speaker terminals and then apply the inverse of this to remove the errors.

Hands down, but i think i will disagree to a certain degree: If we`re talking of a "average tube amp" this make indeed a noticable difference. If we call a solid state amp, in my example a Matrix GT1000 or even more linear amps, like Brystons (i think FAS did use for shooting IRs in the past?!) "averaga power amps", an inversion to flatten out completely the power amps influence will do nearly nothing to the IR result - especially when comparing the influence of different mics and mic-positions.

I tried to discuss this in the past when Clark talks about this approach by using the tube power amp of his Mesa Amp for IR shooting: http://forum.fractalaudio.com/axe-f...k-kent-new-irs-way-teaser-12.html#post1085114

Again: This shows the frequency response of the Matrix GT1000 at its speaker out, while the amp is seeing the load of a 2x12" Speaker cabinet (using a cheap Behringer GI100 DI Box to link through to the cabinet & an direct line-level up-link of the matrix):

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The most influence (non-linearity) we`ll see between ca 1,5kHz and 4Khz (approx. loss of 1db...). IMHO, adjusting the mic half an inch different will make a mulit-times more change to the IR result, no?! I have compared selfmade IRs with the same IR+power amp inversion, the difference is only little audible in the bass department, apart from that nearly inaudible. But as you can see: the loss from up to 10db of the CF200 is not represent by the Matrix:

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Note: This IR was made by a Hughes & Kettner CF200 in PA mode, which shows a much more non-lnearity frequency response, than the Matrix, especially in the inaccurate bass response!

If we talking accuracy, added informations how to tweak the speaker page for IRs of individual Speaker Cabinets would help a giant step better. This is and remain (because by design of a modeller) the missing piece of the puzzle, which can`t be closed automatically, but manually by knowing the behavior of an actual cabinet.

So, the missing piece could only be closed, if we get the needed speaker tab informations of the captured cabinets. IMHO.

Mics, Mic positions & Speaker tab informations influence the result drastic, a good solid state amp assumed, the tool for power amp inversion is a nice one, but with minimal influence to the result, IMHO.
 
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Hands down, but i think i will disagree to a certain degree: If we`re talking of a "average tube amp" this make indeed a noticable difference. If we call a solid state amp, in my example a Matrix GT1000 or even more linear amps, like Brystons (i think FAS did use for shooting IRs in the past?!) "averaga power amps", an inversion to flatten out completely the power amps influence will do nearly nothing to the IR result - especially when comparing the influence of different mics and mic-positions.

Depends on many factors. In some cases the error is relatively small. If the impedance of the speaker varies widely and has a pronounced resonance then the error can be significant. We've measured errors of over 3 dB for some speakers.

This is the reference IR from a 4x12 with D120s. The error is only a couple dB. The power amp was a Matrix GT1000. The scale on the plot is 5 dB/div.

D120_4x12_reference.jpg




Contrast that to this Wizard 4x12. Same power amp.

wizard_4x12_reference.jpg


The Wizard has a much more dramatic impedance curve and this influences the power amp much more.

Multiple measurements are needed to form hypotheses and conclusions. A single measurement using one amp into one particular speaker is not enough data to form a conclusion.

Furthermore you made the mistake of measuring the response at the amp's output terminals. The proper procedure is to measure the response at the speaker terminals (or as close as possible). The resistance of the speaker cable is NOT negligible.

Also the data you plotted is from a sysex file which has insufficient resolution in the low frequencies. The plots above are from the "raw" IRs which are 8K long.
 
Sounds great with a couple of Marshalls I tried it with; it has an interesting "grind" in the upper mids that tunes nicely using the new Slope control...thanks for the IR.
 
Contrast that to this Wizard 4x12. Same power amp.

wizard_4x12_reference.jpg
Woah ... ;) Damn, THIS makes a difference. OK, I`m convinced (in this case).


Good engineers and scientists recognize that multiple measurements are needed to form hypotheses and conclusions. A single measurement using one amp into one particular speaker is not enough data to form a conclusion.
I can`t deny.

Furthermore you made the mistake of measuring the response at the amp's output terminals. The proper procedure is to measure the response at the speaker terminals (or as close as possible). The resistance of the speaker cable is NOT negligible.

When miking a cabinet, when audition a cabinet (for fun or for capturing), the speaker cable is included to the sound you hear (and like). So, if the target is ABing apples to apples (real deal against the digital substitute), i believe the influence of the cable should be included and not be filtered. From this perspective, i think, the speaker cable should be understand as part of the cabinet and be included in the IR.

But again. what do you think about including informations (in a added PDF or so...) with IRs to adjust the speaker page for more accuracy behavior? Would`nt this close the REALLY last gap of accuracy?
 
I tried this IR in different presets and even though cool I felt it to be full, and almost very bassy compared to for example the ownhammer 412 H PR 55 SS median .

Is it something in my preset or listening setup or do you also experience this?

I listen through headphones(Audeze LCD2, latest edition with Fazors).

Just curious.
 
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I tried this IR in different presets and even though cool I felt it to be full, and almost very bassy compared to for example the ownhammer 412 H PR 55 SS median .

Is it something in my preset or listening setup or do you also experience this?

I listen through headphones(Audeze LCD2, latest edition with Fazors).
It's got a full, lower-mid thing going on that adds body and "wood" to the tone—great for '60s through '80s types of sounds. Some players of more modern music my prefer a more scooped IR.

Try Simeon's trick: blend it with a TV for a full-frontal assault that works with lots of different styles.

Also, playing through headphones will give you a different sound than playing at volume or in amix.
 
It's got a full, lower-mid thing going on that adds body and "wood" to the tone—great for '60s through '80s types of sounds. Some players of more modern music my prefer a more scooped IR.

Try Simeon's trick: blend it with a TV for a full-frontal assault that works with lots of different styles.

Also, playing through headphones will give you a different sound than playing at volume or in amix.

Ok. Thanks. I will try that.
 
Ok I changed my mind. I cranked it(through headphones) and sounds KILLER, even without mixing with the TV cab.

Thanks Fractal.
I will definetely buy the new cab pack.
 
Haven't had much time with this yet, but so far "I Like it a Lot" bottom is cleaner and focused and there's a fullness to the upper mids and highs I haven't been able to get exactly right before . :) :)
 
I like this with a lot of the amps that are bass heavy. It doesn't seem to get muddy. On the brighter amps it can get get a bit shrill.
 
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