recording acoustic IRs

gdgross

Experienced
Anyone ever done this? I have a couple acoustics that I love the sound of, and if it's possible, i'd rather use an IR that's truer to the actual guitar than one for a guitar I've never seen nor played.

How does one record an IR for an acoustic guitar? I know how to sweep a speaker input and convolve to get an IR, but how do you do that without an electrical input? (apologies if this has been discussed already, seems like it would have been, but I didn't see anything in my search.)
 
From late last year ...

This is what I'm doing and it's working pretty good although not fool proof. A guy from the Acoustic Guitar Forum developed a way for us all to make our own acoustic IR's that can be loaded into the FM3. You will need a condenser mic and a way to record to make your own IR.

In the FM3, use the TubePre in the amp block and load your custom IR into the cab block. From there, season to taste with reverb, parametric EQ, etc.

https://www.acousticguitarforum.com/forums/showthread.php?t=571361
Further discussion on creating your own custom IRs can be found here ...

http://acousticir.free.fr/spip.php?article136&var_mode=calcul
 
Wow, what an amazing resource, sdtout. Thanks for sharing that. Can’t wait to dig into it a bit.

thanks also nikk - I’ve used the impulse response utility before in logic, actually took IRs of a d-tar Mama bear, that are probably still floating around the internet somewhere. But that’s easy to do with a piece of gear that has an input and an output, or a speaker that you can record. Where do I plug in the sine wave sweep into my acoustic guitar? Lol. Interested to take a closer look at that link on the acoustic guitar forum, hopefully this week...
 
The link I provided last year and the link offered by stdout are from the same source. A sinewave sweep is not done when creating an acoustic guitar IR. One could visualize it as your 60 seconds of playing all over the neck is the sweep. The deconvolution is between the signal the pickup is producing and the signal the mic is producing. The deconvolution of these two creates a mapping (or sorts) from one to the other. It's not perfect but does work. The Octave script generously offered by Jonsfield45 outputs an additional version of the IR that is a 50/50 mix with your original pickup signal. I seem to always have the best luck with the 50/50 mix rather than the full-on IR. I experienced similar things using the Tonedexter. I'm using a Martin D Mahogany 09 that has been tweaked by Bryan Kimsey, Dazzo 60's installed on the bridge plate, and getting very nice tones, at least compared to my previous experience of multiple K&K's, Lyric, and under-saddle piezos.
 
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@caballero59 I quoted your post because that was what alerted me to the resource so the kudos are all to you :)

Bryan Kimsey. That’s a blast from the past. He was really active on the Flatpick list when I used to drop by there but that was years ago. I remember he had pretty trenchant views about amongst other things, the tongue brace. He worked with Mario Proulx who’s a luthier from my general neck of the woods on a model called a OM/D.

http://www.proulxguitars.com/omd.htm
 
@caballero59 I quoted your post because that was what alerted me to the resource so the kudos are all to you :)

Bryan Kimsey. That’s a blast from the past. He was really active on the Flatpick list when I used to drop by there but that was years ago. I remember he had pretty trenchant views about amongst other things, the tongue brace. He worked with Mario Proulx who’s a luthier from my general neck of the woods on a model called a OM/D.

http://www.proulxguitars.com/omd.htm
I should have worded my post more carefully. My intention was to point out that what we both posted was from the same source so people didn't get confused and think there were two streams of thought regarding how to create IRs. You had correctly pointed the reader to the actual specific website which is a great resource.

My wife and I drove to his ranch recently and he kindly pulled my popsicle brace, shaved the back braces, slotted the bridge pins, and did a setup. I'll be honest. In many many cases with youtube comparisons, or changes that I have personally done to guitars and equipment, I often cannot hear much difference. My ears are a little jaded I think. However, this D Hog was already a good guitar (essentially a D-18GE with Alpine spruce top) but over a few weeks, Bryan's mods made a significant difference. I think shaving the back braces was most of it but there is no way to tell.

Anyway, this is all super cool because if you play both electric and acoustic, both can be routed to the FM3 with their appropriate processing.
 
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I wanted to make the piezo pickup on my MusicMan JP6 sound in the direction of my Taylor 616.

To do this, I picked up my Taylor with a Neumann KM84 microphone at about the height of the 14th fret at a distance of about 30cm. In the DAW, with the Magix Samplitude software, I always played the microphone signal as an arpeggio over the open strings and then a Barree' always with a distance of two frets up to the 14th fret.
The piezo output of the JP6 was then recorded synchronously to the reference track in the same way. (You can also try a Strat's neck pickup!)

Now the Taylor track is analyzed with the Samplitude FFT filter and its "sound cloner" functionality, then its spectral fingerprint is saved as a file.
Now it is the turn of the JP6 Piezo track and its offset calculation against the previously created Match FFT preset. This results in a new filter curve that corresponds to the spectral difference between Taylor and JP6. This filter curve must now be converted into an impulse response:
To do this, the first thing to do is to create a test signal, a so-called “chirp”. This is created in Samplitude under "Impulse response acquisition" as a .wav file.
This file is now played back via the previously created difference frequency response via the FFT filter plug-in and a new .wav file is generated via bounce.
Now the Samplitude impulse response extraction module is opened again, here the original chirp and the modified chirp can be loaded under "Impulse response extraction". Now the impulse response can be calculated with "generate", which contains the final IR of the difference frequency response from Taylor and JP6. The .wav file must then be converted into a FractalAudio IR with Fractals CabLab (Free) and can then be loaded into the FM3.
I think you can do this with other tools, there are also other Spectral EQ VST plugins that can transfer frequency response matching to another audio file. And there is the Voxengo Deconvolver, which should then also be able to create an IR from it.
It should also be noted that the best result can only be achieved if the same guitar with the same PU settings that was also used in the clone process is used!

Sorry, that is Google Translator English, i hope you can also understand what i mean!
 
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