Old 07-06-2011, 06:06 PM   #1
flmason
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Default "Defeat" IR's ?

Ran into some IR's on the web that were called "Defeat" IR's... for example to "Defeat SM57" to remove SM57 sound from a track.

Any idea how these are made?

I'm wondering if I could take an inpulse of my mic and monitors... and defeat both in IR, so I'd have a theoretically flat sound coming back out the chain for vocals.

Assuming for a moment this "defeat" thing is some mathematically correct process (not just that someone took Reafir, hand drew an inverse response curve for an SM57 and Impulsed it...) any chance this could be used to remove room sound as well?
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Old 07-07-2011, 07:56 AM   #2
Gizzmo0815
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Default Hmm...

I'm not sure why you'd want to do it. It would be easier to just re-record the track with a different mic...lol.

However, I suspect that it's an IR that was recorded of the equipment response. So an SM-57 IR that is phase inverted which is intended to cancel out the sound of the SM-57. However there are so many variables that would come into play here that would pretty much ensure that you'd never be able to fully cancel the SM-57 "sound" from a recording. You could certainly change the sound by running the recording through an IR but "defeating" it would be realy quite impossible in my opinion. It sounds like marketing gibberish.

What you're describing would be essentially the same as trying to correct monitoring issues with EQ. It wouldn't really work any better in my opinion. Best to just go with the old fashioned methods of room correction.

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Old 07-07-2011, 08:35 AM   #3
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Indeed, it sounds like trying to solve a simple problem with a convoluted (pun intended) solution. It would never precisely cancel the sound out either, unless you record the IR specifically for the purpose using your recording gear in the space and arrangement to be recorded.
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Old 07-07-2011, 05:51 PM   #4
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@Gizzmo - not trying to defeat a mic, but a mic and cheap monitors as well. I.e. yup, trying to solve the "ain't got no studio monitors" problem on the cheap for the moment. So clearly bass traps, etc. aren't on the table either. At least not on this day. Perhaps eventually.

@Kenneth - Yeah basically just trying to get a better shot at making a mix that translates well, on the cheap... and to try and see how much of the sound of the amp sims I'm using comes down to the headphones and speakers I'm using.

Wouldn't expect it to beat traditional solutions, but hey, if it could half the difference, why not try it.

What I haven't figured out is if what gizmo suggests, if a simple phase inversion on the output of say Kefir would do it? I'm thinking not as the EQ curve of an inverted signal is basically the same as the original.

So's the question is really, how to make an IR that cancels the original IR from that perspective, as opposed to say a null test.
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Old 07-07-2011, 07:04 PM   #5
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Honestly, while I don't know what your day job is, chances are that the time you spend on this thread + the time you spend trying to defeat the room would cost you more in time spent (which is money) than if you had just bought/made proper treatment, even one home-made portable bass trap at a time.
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Old 07-07-2011, 07:50 PM   #6
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Quote:
Originally Posted by Kenneth R. View Post
Honestly, while I don't know what your day job is, chances are that the time you spend on this thread + the time you spend trying to defeat the room would cost you more in time spent (which is money) than if you had just bought/made proper treatment, even one home-made portable bass trap at a time.
Honestly, my "day job" has been an up and down career since at least 1995. At times have made six figures. At others gone broke looking for the next job. Long story. Suffice to say, at times I've built a home and had 4 cars and toys, bank account. At others, quite literally debating if it's possible to live in the woods successfully in this age.

Am stuck in a down turn at the minute. The time is more available than the money. Considering that I left a perfectly good Yamaha keyboard at my last residence to move here (ran out of room in the vehicle, had to leave something behind). Had been carting it around since about 2002... new in box... never opened... for my eventual "studio".

So honestly, I'm not up for buying more stuff, as I may have to move again. I seriously despise having to bang up and move equipment. Unlike when I was a kid, "relic" style doesn't appeal to me, LOL! (Didn't even then.)

Serious expenditures are on hold, ideally until I own a home again.

In all reality, the way my work goes, I literally don't have time to fuss with this stuff when I'm working. So I have to get my licks in during the lulls.

Anyway, just managed to figure out how to do an impulse with just MDA Testtone and it gave me some ideas, was wondering what it's limits are as a solution to standard, "cheap recording experiments problems".

Since the mathematical discussion on convolution over on Wikipedia is over my head, haven't ferreted out what the code in something like Kefir actually would do. Or more correctly, what the algorithm is to apply the inherent characteristics of a .wav file to carrier sound stream (assuming it's somewhat like modulation in concept).

Trust me, if I could do things the way I want, I'd just purpose build a high quality, state of the art studio and be done with it.

What a life we each could live, but for $$$. How much we could expand and optimize ourselves and perhaps our world.

The wastage of life that results from not knowing the route to independent wealth by an early age is incalculable.

Being trapped in the working classes sux like that, LOL!
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Old 07-08-2011, 08:04 AM   #7
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I sounds like you're going to go ahead and use the impulses no matter what anyone here says, but let me just add, that you will pretty much always get better results fixing the problem outside of the box (where it is happening) than inside the box.
Room treatment is not expensive or time consuming (as long as you are OK with it not looking great) and setting up your room right isn't complicated.
There is only so much that can be done by manipulating your audio in the computer, and every adjustment you make has the potential to cause just as many problems as it solves.
If your speakers can't hit certain frequecies, or are muddy in areas, then there isn't any real way to extend that low end or clear up the muddiness without changing the acoustic environment. The same with mics, if it's much easier to record it right than to try to "fix" it later. Some great albums have been recorded with a few 57s and a 4 track so you can't say "once I get rid of the sound of this cheap mic my recordings will be great". If your recordings don't sound good through a 57, they won't sound that much better through a u87.
That's not to say that there isn't a time and place for more expensive mics. The right mic can often make the difference between a "good" recoding and a "great" recording, but to blame your mics and room for a mediocre recording is like blaming your car for speeding.
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Old 07-09-2011, 03:53 AM   #8
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I think it is basically EQ. So maybe they have curves that kind of "cancel" the frequency curve of SM57. You could also do that with good EQ and proper specification graph. But you can't get ambience out.

So when talking about monitoring, the same thing applies than with EQs: you can't really repair problems in acoustical space with EQ.

My advice is DIY bass traps, they can be pretty cheap and are not that hard to make. And they really improve things alot.

EDIT: oh and about mics, you should test different ones because even some workhorses like SM57 won't work with every source. If you have special voice or instrument, chances are that stranger mic can do wonders. And it doesn't have to be expensive.

Last edited by gavriloP; 07-09-2011 at 03:56 AM. Reason: forgot something
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Old 07-09-2011, 05:19 PM   #9
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Quote:
Originally Posted by Schmidty View Post
I sounds like you're going to go ahead and use the impulses no matter what anyone here says, but let me just add, that you will pretty much always get better results fixing the problem outside of the box (where it is happening) than inside the box.
Room treatment is not expensive or time consuming (as long as you are OK with it not looking great) and setting up your room right isn't complicated.
There is only so much that can be done by manipulating your audio in the computer, and every adjustment you make has the potential to cause just as many problems as it solves.
If your speakers can't hit certain frequecies, or are muddy in areas, then there isn't any real way to extend that low end or clear up the muddiness without changing the acoustic environment. The same with mics, if it's much easier to record it right than to try to "fix" it later. Some great albums have been recorded with a few 57s and a 4 track so you can't say "once I get rid of the sound of this cheap mic my recordings will be great". If your recordings don't sound good through a 57, they won't sound that much better through a u87.
That's not to say that there isn't a time and place for more expensive mics. The right mic can often make the difference between a "good" recoding and a "great" recording, but to blame your mics and room for a mediocre recording is like blaming your car for speeding.
Don't have any impulses to use. Other than the ones I found labeled "defeat cab" and "defeat sm57" that I found. They were done by someone wanting to use the Simulanalog amp suite with cabinets other than the built in one.

Was wondering if there's a way to take an existing impulse and "invert it" so to speak, so that it becomes a "defeat".

Pretty much an just an idea for an experiment.
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Old 07-09-2011, 05:21 PM   #10
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Quote:
Originally Posted by gavriloP View Post
I think it is basically EQ. So maybe they have curves that kind of "cancel" the frequency curve of SM57. You could also do that with good EQ and proper specification graph. But you can't get ambience out.

So when talking about monitoring, the same thing applies than with EQs: you can't really repair problems in acoustical space with EQ.

My advice is DIY bass traps, they can be pretty cheap and are not that hard to make. And they really improve things alot.

EDIT: oh and about mics, you should test different ones because even some workhorses like SM57 won't work with every source. If you have special voice or instrument, chances are that stranger mic can do wonders. And it doesn't have to be expensive.
Yeah, I hear what you're saying.

I was hoping that the impulse, having the eq and time domain stuff in it would, when "inverted", cancel it all out.

I suppose I could sit there with white noise and an analyzer and use ReaFir to try and force the white noise back to a flat line, if EQ where the only problem present.

Naturally I'd rather do this the right way, just not at option at this time.
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Old 07-09-2011, 05:35 PM   #11
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Quote:
Originally Posted by flmason View Post
Don't have any impulses to use. Other than the ones I found labeled "defeat cab" and "defeat sm57" that I found. They were done by someone wanting to use the Simulanalog amp suite with cabinets other than the built in one.

Was wondering if there's a way to take an existing impulse and "invert it" so to speak, so that it becomes a "defeat".

Pretty much an just an idea for an experiment.
if the words 'experiment' and 'impulse response' interest you -
then i must link to Johnymcfly @ Acmebargig who made this weird monster that i've not yet played with:

http://www.acmebargig.com/product/ir-a-live2/
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Old 07-09-2011, 07:47 PM   #12
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Quote:
Originally Posted by BenK-msx View Post
if the words 'experiment' and 'impulse response' interest you -
then i must link to Johnymcfly @ Acmebargig who made this weird monster that i've not yet played with:

http://www.acmebargig.com/product/ir-a-live2/
Somewhere on the web I tripped over a page that the author claimed he'd somehow gotten impulses of Metallica Recordings. Not sure if it's something like this. Perhaps not, as well. Not really sure.

I seem to remember some plugin that was aimed at forcing the EQ of one track to match another, some years back.
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Old 07-11-2011, 07:44 AM   #13
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IR-A-LIVE is missing one component, that is real time deconvolution. I have a comment on the main posting too, but I want to make sure we don't confuse the intended purpose of IR-A-LIVE, so I want to take a sec and explain that.

As I said IR-A-LIVE is missing one component, that is real time deconvolution. However that depends on how you want to use it. The goal was to provide something that replicates 100% accuracy on everything your speaker is doing through convolution.(That is the goal, we're not stating it does this, yet). Quite a tall order for sure as deconvolution can be expensive in terms of CPU among other factors. However, the idea was to be able to take a full track being recorded in real time, deconvolve the signal, and send that track to a convolver. IR-A-LIVE represents the convolver portion of this scenario. Most IR cab files are quite small, 4-12 ms, IR-A-LIVE is unlimited in IR File size, but not block size, it takes a block size of 2048 samples.

So the user would have a live mic on their cabinet, and a signal from their head. Remove the head from the cabinet, then send that signal into IR-A-LIVE. IR-A-LIVE then convolves using that signal and a live signal coming from your guitar, thus performing convolution on a signal that represents what your cabinet is doing at the time.(Theoretically, and is not yet proven)

Thats a non-static scenario. In a static scenario one would record their tracks to finality, meaning you are not going to change anything, and then you would deconvolve the cabinet and head only tracks creating a third track which becomes the IR file used by IR-A-LIVE.

I want to spend some more time on IR-A-LIVE as soon as we get Head Case released to make it more user friendly and less freaking confusing... I should also point out at this time that a lot of this is theoretical meaning that we have not 100% tested this as it is part of our R&D. I'm sure there is alot left to learn and certainly is aspects that we have yet to think about, but the idea is there, and working without the deconvolver portion.

BOT:
The Mettalica recordings were not done by us, but there is a guy who has made various Mettalica Cab IR files based on the actual recordings. What we did do, was incorporate the Matrix CAB IR series into Shred 1.5x(Now head case) and Matrix makes cabinets based on actual recordings. However, thats not us, thats Matrix and the guy who makes the Golden Mettalica IR pack.
You can get both at Guitarampmodeling.com.

Defeat 57
I am not sure that you would ever really get that defeat IR to work as one may think. I would assume that the defeat IR would have to be applied to the same original cabinet IR in order to be accurate. Like if you have a cab recorded with a 57 and defeat it does that mean you can apply the profile of a 441? I am not sure, and at the end of the day its just a filter, so would one be better off using an EQ to get to the sound they are looking for? My guess is yes. In terms of pure exploration and research, it makes an interesting topic for sure.

So...
Cab recorded with 57 - Head(most likely DI OUT?) = Cab recorded with 57
Cab recorded with 57 - 57 = Raw cabinet

How does one get the recording of the 57 alone in order to get to the raw cabinet? Thats the question that needs answering...What if a car drove down the road 5 miles away while you were making the original IR, How does that affect the accuracy? What about line noise? how does that affect the outcome?

Its pretty questionable in the end..
I don't know, I am certainly interrested in knowing the answers for the above questions though.
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Old 07-11-2011, 04:17 PM   #14
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Quote:
Somewhere on the web I tripped over a page that the author claimed he'd somehow gotten impulses of Metallica Recordings.
Sweet, I hope it cancels out that horrible smashing/compression of the audio signal into complete silence.
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Old 07-11-2011, 04:30 PM   #15
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isn't this what antares mic modeler did?
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Old 07-11-2011, 07:17 PM   #16
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@karbo, here's the link for the Mettalica IR files...
http://www.guitarampmodeling.com/viewtopic.php?
f=32&t=12309&p=67967&hilit=golden+mettalica#p67967

@Jason
Yes I believe thats how it works, but I'm not sure how they are doing it..
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Old 07-11-2011, 08:16 PM   #17
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@karbo, here's the link for the Mettalica IR files...
http://www.guitarampmodeling.com/viewtopic.php?
f=32&t=12309&p=67967&hilit=golden+mettalica#p67967
Lol, that was a joke actually. I was sort of asking if it could convolve their over-compressed-smashed-into-oblivion-commercial-mixes into complete silence.
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Old 07-11-2011, 08:33 PM   #18
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haha Sorry man, I am in a constant state of rushing these days to get stuff done and keepup with posts. I'll read more careful next time..

Anyways yeah those mixes are a little lifeless aren't they, not like Kill em all
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