Amp-in-the-room IRs

DLC86

DLC86

Fractal Fanatic
I've read a lot of discussion here and on TGP about far field IRs and how they should provide the closest result to match a cab frequency response heard live-unmiked according to experts like Jay Mitchell and Cliff himself. But when trying those, even if they're better at this than close-miked IRs (don't have exagerate highs and lows, are less affected by mic positioning, exhibit less destructive interferences in some frequencies, etc..), they still fail on one point IMHO: they still sound "phasey" like a miked IR.
This is because (at least from my understanding) far field IRs are captured at a certain distance from the speaker but the mic is not far enough from it to "view" the speaker as a point sound source, so the capture is still affected by the constructive/destructive interferences caused by the sound waves coming from different points of the speaker surface, that's what causes that phasey sound. That's also what happens when you "capture" the sound with your ears but having those cancellations already included in the IR is like they're happening twice (first time from the mic capture, second time from you ears in front of a FRFR speaker).
The dephase parameter works great in this regard but I think it's not an "accurate" way of solving the problem.
The (impractical) solution to this would be to capture the IR from a far greater distance but it will probably be impossible to not have ambience reflections or noises coming thru.

So here comes my (probably stupid) idea:
If we capture a far field IR of a cab and another far field IR of a reference FRFR coaxial speaker (built as similar as possible to a guitar cab - e.g. Atomic Clr - and captured at the same exact distance, room, same mic and position) and tonematch those two wouldn't the resulting IR give that FRFR speaker the same "overall" frequency response of the cab without the phasiness issue?
I know that it won't be a simple task to compensate for all the variables involved in the process and that will probably be other differences such as dispersion pattern for example, but maybe this could provide a more realistic result to amp-in-the-room chasers.
What do you think?
@FractalAudio?
 
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Some time ago I experimented with combining near and far IRs. They did not combine in an adequately convincing fashion.

An amp in the room is part of the room: its a speaker beaming sound and the cabinet resonating in the whole space; sound going in all directions, bouncing around with time and phase interactions. If you reproduce a recording of an amp in the room; it sounds weird and unnatural if it isn't in the same room because the ear is getting information that doesn't match the space, and this discrepancy of perception is interpreted as something being really off.

Part of the issue (IMO) is the difference between the conditioned preference for recorded tones in a mix vs the actual sound of the amp in space. The conditioned response is that the sound should correspond with the mental inventory, a subconscious reference: for most people this is derived largely from recordings - which are close miked: and EQed for the purpose of punching through the mix, which is often not ideal for an ambient "in the room" experience.

For IRs I made; I arrived at close micing (12-20cm) with a relatively neutral mic that doesn't have an excessive proximity effect or high end response and has an off axis response that mitigates phase artifacts. (I like the Beyerdynamic M160 with its hypercardioid pattern). Might as well just use available IRs. The factory Fractal M160 IRs I've tried were certainly up to the job; others as well, I'm sure. EQed to taste. Probably lower the resonance amount in the cab block: Not as punchy: but more "in the room" Adding reverb later carefully tailored to the specific performance space is as close as I can get. This is where you'll really appreciate the quality of the Fractal reverbs.

So, other than using an actual cabinet in a room: an IR EQed to taste with reverb is my recommendation. Don't underestimate the importance of tuning the reverb to the room: the early reflections, room size, decays, density, feedback, etc. are all crucial in achieving a satisfactory result.
 
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I've found that the TAF near/far mixes fit into a mix with a lot less post processing, are more natural sounding, but then that's for recording, not live in the room..
 
artzeal said:
An amp in the room is part of the room: its a speaker beaming sound and the cabinet resonating in the whole space; sound going in all directions, bouncing around with time and phase interactions. If you reproduce a recording of an amp in the room; it sounds weird and unnatural if it isn't in the same room because the ear is getting information that doesn't match the space, and this discrepancy of perception is interpreted as something being really off.
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Yes I agree with that and what I was trying to say has to do with what you say but my point was a bit more "theorical": when reproducing a sound thru a good FRFR speaker it's happening about the same thing, it is also a speaker beaming sound in all directions and resonating in a space, the only differences with a guitar cab are the frequency response of the speaker and his dispersion pattern.*
So to achieve a real "Amp In The Room Experience"® we'd need something that shapes the flat response of the FRFR to match the frequency response of the guitar cab we want to emulate. And here far field IRs come into play.
Obviously if we use an IR that includes room reflections and play thru a FRFR inside an actual room it's like all this is happening twice, but far field IRs should not contain any room reflection. They are captured with a flat response reference mic placed in the far field (2 meters or more) cuz their aim is to capture the frequency response of the whole speaker surface.
The problem is that those 2 meters (for which is already difficult to capture a room-reflections-free IR) are not enough to do it without phase cancellations, you'd need a far greater distance but in that case it would be an impossible task to not capture reflections too.
That's why I was asking if my idea on the tonematch is theorically right and if it can be a good workaround for this task.

*= a good FRFR cab should not have prominent internal resonances and the IR would reproduce the ones of the guitar cab.
artzeal said:
Part of the issue (IMO) is the difference between the conditioned preference for recorded tones in a mix vs the actual sound of the amp in space. The conditioned response is that the sound should correspond with the mental inventory, a subconscious reference: for most people this is derived largely from recordings - which are close miked: and EQed for the purpose of punching through the mix, which is often not ideal for an ambient "in the room" experience.
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I totally agree with you on this, in fact now 90% of the times I prefer a miked sound and it's way better when playing in large venues or thru a PA. But when playing in small pubs where only the voice is miked sometimes I miss that sensation of filling the space with the sound of an actual cab.

artzeal said:
For IRs I made; I arrived at close micing (12-20cm) with a relatively neutral mic that doesn't have an excessive proximity effect or high end response and has an off axis response that mitigates phase artifacts. (I like the Beyerdynamic M160 with its hypercardioid pattern). Might as well just use available IRs. The factory Fractal M160 IRs I've tried were certainly up to the job; others as well, I'm sure. EQed to taste. Probably lower the resonance amount in the cab block: Not as punchy: but more "in the room" Adding reverb later carefully tailored to the specific performance space is as close as I can get. This is where you'll really appreciate the quality of the Fractal reverbs.

So, other than using an actual cabinet in a room: an IR EQed to taste with reverb is my recommendation. Don't underestimate the importance of tuning the reverb to the room: the early reflections, room size, decays, density, feedback, etc. are all crucial in achieving a satisfactory result.
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Actually I've already achieved pretty good results mixing different cabs and using dephase and smoothing, but thanks anyway for this precious suggestions, there's surely something new I can try to make them even better. ;)
And I agree with you again on the importance of the reverb block, it really can make or break a sound but Fractal quality makes it lean towards the latter.
My go-to are studio C, medium room and london plate
 
DLC86 said:
Yes I agree with that and what I was trying to say has to do with what you say but my point was a bit more "theorical": when reproducing a sound thru a good FRFR speaker it's happening about the same thing, it is also a speaker beaming sound in all directions and resonating in a space, the only differences with a guitar cab are the frequency response of the speaker and his dispersion pattern.*
So to achieve a real "Amp In The Room Experience"® we'd need something that shapes the flat response of the FRFR to match the frequency response of the guitar cab we want to emulate. And here far field IRs come into play.
Obviously if we use an IR that includes room reflections and play thru a FRFR inside an actual room it's like all this is happening twice, but far field IRs should not contain any room reflection. They are captured with a flat response reference mic placed in the far field (2 meters or more) cuz their aim is to capture the frequency response of the whole speaker surface.
The problem is that those 2 meters (for which is already difficult to capture a room-reflections-free IR) are not enough to do it without phase cancellations, you'd need a far greater distance but in that case it would be an impossible task to not capture reflections too.
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You just gave me an idea. On a blistering hot August day a few years ago, my drummer and i went up to the local university parking lot, which is huge but virtually empty in summer and is surrounded by woods on three sides (good for absorption of echos from buildings), and we set up his drum kit and a portable Recorder/monitor and reference track to play to (easy to do 24 bit digital records remotely these days) and put up a few mics around the kit including stereo overhead - and the results were amazing. I've never heard a drum kit recording so clear, crisp, and clean. So after reading your comment, i think i might go back and do some far field IRs of cabs without any room on them at all.
I think the best way might be to place the cab on it's back, on some moving blankets, or squash bass, or... and place mics above. Just thinking out loud, but you never know what will work in an IR mix until you try.

As far as FRFR v. amp cab, and getting amp in room - An IR gets you the tone of a speaker in cab by matching the frequency of the speaker/cab and the mic. - so you might want to subtract the mic tone from the IR. (i think this can be done with the AFX, can it not?) - Once you have the raw frequency output of your amp cab, you can put this out an FRFR faithfully - but the dispersion still needs to be taken care of - for a typical amp cab it's cardioid pattern and hyper-carioid at higher frequencies, like a beam of light, so you get a different tone completely in your ears depending on where you stand - you can move around the room and find the place you like, based on the tone right there in that spot. Get tired of that tone, just take a few steps.

So maybe an FRFR with the same beam like dispersion of an amp cab is the best way. I think there are some folks working on this - has anybody here tried them out? Then you get the dispersion you want, and the virtual cabs will still work as designed - a win win.
 
Oh, one more thing. I can see why some say that a far-fiend IR works best to achieve the 'in the room' sound, because it approximates the tone of the cab from the most listening positions (IE not or close to on axis), but in order to get it right, i think you need a tight close representation IR, no room at all - extract mic tone, combined with an FRFR (so you can switch cabs in AFX) that has the same dispersion pattern as a typical amp cab.
The FRFR could be either four 12" FRFR elements in a standard amp cabinet, or something like the CLR, but with variable pattern output - from omni to cardioid or fixed at cardioid.
 
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What barhrecords said, except I'd take far more captures from different positions. I find most 4x12s sound best tilted back 11-13 degrees (note, huge tonal variation in this range). Then move the mic at small intervals (usually I move it 1cm or less) from the on-axis position. Even at 2 metres, the IR will sounds drastically different with the mic moved 1cm off axis. The key is to find the right position that sounds the least phasey (generally the more off axis, the phasier the sound, but too on axis can be harsh). Lately, I have been capturing over 100 IRs per cab, but only a small portion of these are actually useable (ie, not sounding phasey). It just takes patience and experimentation.
 
BillyZeppa said:
You just gave me an idea. On a blistering hot August day a few years ago, my drummer and i went up to the local university parking lot, which is huge but virtually empty in summer and is surrounded by woods on three sides (good for absorption of echos from buildings), and we set up his drum kit and a portable Recorder/monitor and reference track to play to (easy to do 24 bit digital records remotely these days) and put up a few mics around the kit including stereo overhead - and the results were amazing. I've never heard a drum kit recording so clear, crisp, and clean. So after reading your comment, i think i might go back and do some far field IRs of cabs without any room on them at all.
I think the best way might be to place the cab on it's back, on some moving blankets, or squash bass, or... and place mics above. Just thinking out loud, but you never know what will work in an IR mix until you try.
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That's a nice idea indeed ;)
BillyZeppa said:
As far as FRFR v. amp cab, and getting amp in room - An IR gets you the tone of a speaker in cab by matching the frequency of the speaker/cab and the mic. - so you might want to subtract the mic tone from the IR. (i think this can be done with the AFX, can it not?) - Once you have the raw frequency output of your amp cab, you can put this out an FRFR faithfully - but the dispersion still needs to be taken care of - for a typical amp cab it's cardioid pattern and hyper-carioid at higher frequencies, like a beam of light, so you get a different tone completely in your ears depending on where you stand - you can move around the room and find the place you like, based on the tone right there in that spot. Get tired of that tone, just take a few steps.

So maybe an FRFR with the same beam like dispersion of an amp cab is the best way. I think there are some folks working on this - has anybody here tried them out? Then you get the dispersion you want, and the virtual cabs will still work as designed - a win win.
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Regarding the mic coloration, far field IRs should be captured with neutral measurement mics so it won't be a problem. But it won't be capturing the response of the cabinet faithfully anyway, because the mic is still "hearing" different points of the speaker surface and those multiple sound waves reach the mic at different moments causing phase cancellations. It's like applying a short delay (less than 1ms) with some feedback, it produces comb filtering, that's what we percieve as "phasiness".
This effect is more prominent with close mic'ing and it becomes less noticeable the more you move the mic away. But 2 meters are still not enough to eliminate it, the proof is what @antcarrier says: the sound, even at 2 meters, changes drastically if you move the mic by just 1cm. This is caused exactly by these phenomenon.
And even finding the sweet spots where this problem is less pronounced it still isn't a faithful representation of the cab response.
But the idea he proposes to capture various position of the mic and mix them is a good one and another possible workaround ;)
BillyZeppa said:
Oh, one more thing. I can see why some say that a far-fiend IR works best to achieve the 'in the room' sound, because it approximates the tone of the cab from the most listening positions (IE not or close to on axis), but in order to get it right, i think you need a tight close representation IR, no room at all - extract mic tone, combined with an FRFR (so you can switch cabs in AFX) that has the same dispersion pattern as a typical amp cab.
The FRFR could be either four 12" FRFR elements in a standard amp cabinet, or something like the CLR, but with variable pattern output - from omni to cardioid or fixed at cardioid.
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I agree with this and a proper far field IR should not contain any room reflection, but I see the wider dispersion pattern of the FRFR as a feature and something not directly related to my idea of amp-in-the-room. It's something I always desired when playing with guitar cabs indeed.
 
I'll add that in my experience, the "phasey" tone associated with far field IRs is directly related to the presence of a notch in the frequency response typically between 1-3kHz. Sometime this can be severe, as much as -20db in this area - which is similar to having an inverted cocked wah pedal engaged. This is typical speaker behaviour I expect is caused by a speaker's cone edge resonance, whereby essentially the vibrating wave of the speaker cone hits the outer edge, then bounced back into the cone out-of-phase - this causes cancellation of sound at these frequencies I mention.

Room reflections, combined with listening position, can blur this effect (measurably - room IRs will not always have this frequency notch), which is what we hear when we listen to a cab in a room - so we don't notice all these imperfections (present in the speakers themselves) when we play through a physical cab, because the room is essentially making the speaker sound tolerable. The problem is, a far field IR must be anechoic, because obvious room reflections sound terrible in the far field for cab IRs, because they are far too loud and sound like a muddy mess (due to cab IRs needing to be mixed 100% wet in order to work, unlike reverb IRs). Also note that close miked IRs mask this notch effect significantly.

Unfortunately if you capture a FF IR 100% dry (like I do), you capture all the speaker's imperfections such as this notch filter. When played back through an accurate FRFR system, this filter effect is preserved and reproduced by your monitor. This time around, the room (& listening position) can no longer compensate for the guitar speaker's cone edge resonance, which I can only assume to be related to the directivity behaviour of guitar speakers, combined with the listening position being "baked in" to the IR.

It's a pain in the ass to work around.

But it can still be done ;)
 
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antcarrier said:
I'll add that in my experience, the "phasey" tone associated with far field IRs is directly related to the presence of a notch in the frequency response typically between 1-3kHz. Sometime this can be severe, as much as -20db in this area - which is similar to having an inverted cocked wah pedal engaged. This is typical speaker behaviour I expect is caused by a speaker's cone edge resonance, whereby essentially the vibrating wave of the speaker cone hits the outer edge, then bounced back into the cone out-of-phase - this causes cancellation of sound at these frequencies I mention.

Room reflections, combined with listening position, can blur this effect (measurably - room IRs will not always have this frequency notch), which is what we hear when we listen to a cab in a room - so we don't notice all these imperfections (present in the speakers themselves) when we play through a physical cab, because the room is essentially making the speaker sound tolerable. The problem is, a far field IR must be anechoic, because obvious room reflections sound terrible in the far field for cab IRs, because they are far too loud and sound like a muddy mess (due to cab IRs needing to be mixed 100% wet in order to work, unlike reverb IRs). Also note that close miked IRs mask this notch effect significantly.

Unfortunately if you capture a FF IR 100% dry (like I do), you capture all the speaker's imperfections such as this notch filter. When played back through an accurate FRFR system, this filter effect is preserved and reproduced by your monitor. This time around, the room (& listening position) can no longer compensate for the guitar speaker's cone edge resonance, which I can only assume to be related to the directivity behaviour of guitar speakers, combined with the listening position being "baked in" to the IR.

It's a pain in the ass to work around.

But it can still be done ;)
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I concur that there can be weird things happening and you clearly have more experience than me in shooting IRs.. However, are u sure that this notch is caused by some cancellation on the cone itself? If it is it should be present independently of where you place your mic, in a reflection-free IR. And it should be considered part of the response of the speaker in this case.
If it varies in intensity and frequency depending on mic position then it means it's happening "in the air" so it could be just one of the phase cancellations I was talking about.

If you think about it it's the same thing that happens when you mix two IRs where one is delayed or out phase in relation to the other, it's plausible that the cause could be the same even in this case (various points of the speaker surface can be considered different out-of-phase or delayed sound sources)

Out of curiosity, has anyone ever tried to shoot an IR of a Frfr cabinet?

EDIT: re-reading your post I get that it's indeed something happening on the speaker surface and probably a FRFR cabinet just accentuates this because of its wider dispersion.
But I'm not gonna get rid of my CLRs 90°x90° dispersion just for this issue :cool:
 
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DLC86 said:
I concur that there can be weird things happening and you clearly have more experience than me in shooting IRs.. However, are u sure that this notch is caused by some cancellation on the cone itself? If it is it should be present independently of where you place your mic, in a reflection-free IR. And it should be considered part of the response of the speaker in this case.
If it varies in intensity and frequency depending on mic position then it means it's happening "in the air" so it could be just one of the phase cancellations I was talking about.

If you think about it it's the same thing that happens when you mix two IRs where one is delayed or out phase in relation to the other, it's plausible that the cause could be the same even in this case (various points of the speaker surface can be considered different out-of-phase or delayed sound sources)

Out of curiosity, has anyone ever tried to shoot an IR of a Frfr cabinet?

EDIT: re-reading your post I get that it's indeed something happening on the speaker surface and probably a FRFR cabinet just accentuates this because of its wider dispersion.
But I'm not gonna get rid of my CLRs 90°x90° dispersion just for this issue :cool:
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Well, assuming there something to this, it can be quantified and removed or deconvoluted, right?
 
BillyZeppa said:
Well, assuming there something to this, it can be quantified and removed or deconvoluted, right?
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As I said if it's a behaviour of the speaker cone itself there's no reason to remove it IMHO (if our purpose is to capture the freq response faithfully)
 
DLC86 said:
As I said if it's a behaviour of the speaker cone itself there's no reason to remove it IMHO (if our purpose is to capture the freq response faithfully)
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Ya, that does make sense, provided that the FRFR system in question doesn't have the same 'cone-cancellation' problem, or you end up with two of them compounded.
 
I'm not sure i understand your idea as explained in your OP. Could you possibly unpack it a little more explicitly, and, do you know if FRFR solutions produce this same cone cancellation as normal amp cabs?
 
BillyZeppa said:
I'm not sure i understand your idea as explained in your OP. Could you possibly unpack it a little more explicitly, and, do you know if FRFR solutions produce this same cone cancellation as normal amp cabs?
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Imagine to capture a far field IR: you place a reference mic at a certain distance from the cab in an anechoic environmente and shoot the IR that will contain certain cancellations. Then take out your cab and replace it with a coaxial Frfr speaker of the same size, place it in the same exact position where your cab's speaker was (this need to be extremely precise) and shoot the IR. This IR (if the two speakers have the same exatct shape) will contain the same cancellations of the first, the only differences would be the raw frequency response of the 2 speakers.
If you tonematch these 2 IRs the result would be an IR that just compensates for the differences in the 2 frequency responses "cancelling" out the cancellations :D

Now that I write it this way I see the limitations of the process though.. It's practically impossible to find an Frfr speaker with the same shape of a guitar speaker (for example a coaxial one would have a tweeter where the other has a dust cap) so it probably won't create the same cancellations, but maybe this method could work great for matching 2 guitar speakers of the same size.

To answer your 2nd question: I don't know if a Frfr has the same cone cancellation, I assume it depends on the design and could also be compensated with DSP processing and/or crossover. From what I hear my Clr doesn't have big dips in its response
 
barhrecords said:
@antcarrier do you prefer 2m microphone distance vs. 3m?

And do you post process the IR wav files to correct for time of flight and window the IR tail?
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I use 2 meters because the roof where I record is too low to record at 3 meters without room reflections within 21ms, although I have tried making shorter 3 meter IRs that still sound good. I do edit the IRs to remove time of flight, but I haven't been applying a window to the IRs.

I was under the impression that the fractal cab block did its own windowing, and that applying a window would be 'doubling up' so to speak. That said, now that hi res and ultra res are in the same cab mode, it may be worth me adding a window to the files, since they are shorter. I have actually recently started using ultra res mode for IRs already cropped to 21ms, because ultra res mode sounds better to my ears even with short IRs (I have no idea why, perhaps related to the window in normal res mode?). I haven't actually read up on windowing in detail because I've not bothered applying it as I thought the cab block did it - is the main benefit reduced aliasing?
 
BillyZeppa said:
I'm not sure i understand your idea as explained in your OP. Could you possibly unpack it a little more explicitly, and, do you know if FRFR solutions produce this same cone cancellation as normal amp cabs?
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If an FRFR system is designed properly, this won't be an issue.
 
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