IR Tech Talk

I'm considering trying third party cab packs and have a few questions about how they're captured, not sure if the actual IR vendors reply here, or maybe users who know the answers can chime in and shed some light on the subject.

1) Are IRs dependent on the power applied to the speaker? I would think speakers' character change depending on how hard they're driven, and if that is true, at what power rating do IR vendors capture their IRs? Do IRs capture the mechanical inertia diference between low and high amplitude signals?

2) Are IRs captured in anechoic chambers? I'd imagine for accuracy purposes that would be the ideal scenario, but do IR vendors actually do it?

3) Are there IR vendors who publish their IR resonance frequencies, or is this information available elsewhere?

4) Why aren't there more off-axis IRs available? If you'd ever tried listening from where most IRs are captured you'd realize how awful that sounds. My best shot using a single SM57 is off-axis about 1" from the speaker, mic perpendicular to the cone surface, wondering why there aren't more offerings captured this way. Or maybe there are and we're just not told about it?

5) Are there known shortcomings of IR capture technology, including the interaction between amp models and IRs vs real amps and real speakers?
 
Hi Deny,

I'll try.

1. The power amp does influence the IR, alot. This can be good and bad, I personally like to experiment with everyone I get my hands on :)

2. Yes and no. Creating them is an art just as micing a real amp. Room/air is good for certain things.

3. Not sure.

4. Personally I mic from many traditional and non traditional angles and get nuetral, bright and dark results. The idea it to match as many preferences as I can at the same time giving user the abiliy to mix IRS that are diverse to fine tune their tone.

5. IRs behave for the most part just as the speaker would though with so many tone shaping options available in the Axe we can bend the tone amazingly well.

One thing to note, each IR maker has a style in a way, which makes them unique. I find switching even from IR to IR can create a whiplash effecting perception of the tone. For me I find a neutral amp setting ideal to start with. Find an IR you like the basic sound of the adjust from there. Hope this isn't too obvious, but even dark or bright IRS can have something to offer with tilt eq or even mixing dark and bright together. So say a r121 and a sm57 can create a great to e texture.
 
3) Are there IR vendors who publish their IR resonance frequencies, or is this information available elsewhere?
I know that cabir.eu and valhallir.at provide this info. I've seen it on one or two free IRs, but I don't know any other commercial vendors who do this. Both vendors are active in the german Axe-forum, where this has been discussed at length. We consider this an important information and we don't really know why others don't provide it.

About the other questions, they are really good ones and I'd love to have detailled answers from all commercial vendors. But I don't think we can expect answers here.

1) Ever since firmware Q9 (afair) the Axe can simulate the change in tone when the speaker is driven with different power levels. Based on this I'd say it would be best to capture IRs with as little output as possible. But the signal to noise ratio gets worse with lower output. As always in nature it's a matter of balance between two evils ;)
2) I don't think they do this! But - comparable to 1) - I'd expect this to be the ideal case. Capturing the cab only without room would be nice, because then we could simulate the room with a reverb only. BUT: The reverb doesn't replicate the whole scenario, e.g. different distances to the floor, ceiling and walls etc.
5) IRs are completely linear. Non-linear effects cannot be captured. But guitar speakers, especially when driven hard, behave non-linear. That's why this non-linearity has to be simulated, see 1)

That's all I know or what I THINK I know. Corrections are always welcome :)
 
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I'm considering trying third party cab packs and have a few questions about how they're captured, not sure if the actual IR vendors reply here, or maybe users who know the answers can chime in and shed some light on the subject.

1) Are IRs dependent on the power applied to the speaker? I would think speakers' character change depending on how hard they're driven, and if that is true, at what power rating do IR vendors capture their IRs? Do IRs capture the mechanical inertia diference between low and high amplitude signals?

2) Are IRs captured in anechoic chambers? I'd imagine for accuracy purposes that would be the ideal scenario, but do IR vendors actually do it?

3) Are there IR vendors who publish their IR resonance frequencies, or is this information available elsewhere?

4) Why aren't there more off-axis IRs available? If you'd ever tried listening from where most IRs are captured you'd realize how awful that sounds. My best shot using a single SM57 is off-axis about 1" from the speaker, mic perpendicular to the cone surface, wondering why there aren't more offerings captured this way. Or maybe there are and we're just not told about it?

5) Are there known shortcomings of IR capture technology, including the interaction between amp models and IRs vs real amps and real speakers?
For answers to 1, 2, and 4, I have written extensively about my methodology here (please click to expand the each tab on my site ):

https://www.drbonkerssoundlab.com/why-dr-bonkers/
https://www.drbonkerssoundlab.com/faq/

Regarding the resonant frequency, where the manufacturer publishes it on the speaker, I give you a picture of it. Where the manufacturer does not publish it, I do not. I am a recording engineer by trade and was able to capture many a good cab sound without such info, also I do not have the tools to measure this. Many of my clients seem to agree that I capture good sounds.

Once I have made back my initial setup investment, I will explore this measuring capability, but truthfully very few clients have ever asked me for this info (not even 1%), so I am not sure how large the audience even is for such info.
 
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