# How to create acoustic guitar impulse response?



## tcollins (Jan 26, 2014)

Or, should I bother?
I'm looking for a way to warm up sampled guitars, especially for strum simulation. Among other things, I thought about putting Kontakt's convolution effect to work. After much googling, it seems that there are 2 methods for creating an IR; (1) Use a swept sine wave with a speaker and mics, and then use software to separate the original signal from the recorded result (phase invert?). Or (2), Whack the guitar with something and record the resulting noise. Option 2 is obviously easier to implement. I understand that Logic Pro comes with a utility that can be of use for option 1, but I'm a DP guy at the moment.

Have any of you tried recording and using instrument body IRs? Do you process the resulting .wav file in any way before loading it into Kontakt? 

As I said, I did try to find info on this, but all of the experts are here in my own neighborhood, so any advice would be appreciated. 

Best,
Tracy


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## d.healey (Jan 26, 2014)

Voxengos deconvolver is good for making IRs. Stick a speaker inside the guitar body through the sound hole and have it play a sine sweep or MLS, point a microphone at the sound hole and record the resultant sound then process if with voxengo.

You may want to damp the guitar strings. It's also best to do this sort of thing in an anechoic room but I'm guessing you don't have one of those  so just use a room that's as dry as possible and perhaps acoustically shield the microphone from all directions except the guitar sound hole.


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## Luca Capozzi (Jan 26, 2014)

For resonant bodies I use a stiff mallet, usually of same material as the body I want to capture. For guitars, I usually hit on the bridge, without strings. 

Cheers,
Luca


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## tcollins (Jan 26, 2014)

TotalComposure @ Sun Jan 26 said:


> Voxengos deconvolver is good for making IRs. Stick a speaker inside the guitar body through the sound hole and have it play a sine sweep or MLS, point a microphone at the sound hole and record the resultant sound then process if with voxengo.
> 
> You may want to damp the guitar strings. It's also best to do this sort of thing in an anechoic room but I'm guessing you don't have one of those  so just use a room that's as dry as possible and perhaps acoustically shield the microphone from all directions except the guitar sound hole.



Thank-you. This seems like a possible solution. It would seem that the choice of speaker would be important, and how it interfaces with the guitar body (whether it is somehow isolated from the guitar interior or touches it). Or, since the strings excite the guitar body at the bridge, maybe the speaker could be held against the bridge. Just thinking out loud here.


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## tcollins (Jan 26, 2014)

Luca Capozzi @ Sun Jan 26 said:


> For resonant bodies I use a stiff mallet, usually of same material as the body I want to capture. For guitars, I usually hit on the bridge, without strings.
> 
> Cheers,
> Luca



Thanks, Luca. So I would record the result (stereo) and use that wav as the IR to be loaded? Do you include the initial impact of the mallet, or do you edit that out?


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## tcollins (Jan 26, 2014)

Thanks again for the replies. I'll experiment and see where things lead me!


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## tcollins (Feb 3, 2014)

Well, today I had a chance to experiment, and I can't remember the last time I had so much fun and got so excited about the results. Within 10 minutes I had dramatically improved the sound of a sampled acoustic guitar!
I held the guitar with the strings damped and mics (x/y configuration) about 8 inches away, and tapped the bridge with a small piece of wood. The recording was edited down to about 1.5 seconds and faded. The beginning was edited to start at the highest point of the opening transient. 
I loaded it into Kontakt's convolution effect and it was magic. Played with eq-ing and whacking guitars the rest of the day. Thanks for the tip!


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## MacQ (Feb 3, 2014)

It's good fun, especially putting non-acoustic sources through the guitar IRs. I can't help but think a dynamic IR would be more effective, but then Sintefex has the patent on dynamic convolution, so I'm not sure it's even a possibility for someone to attempt. It is interesting, though.


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## tcollins (Feb 4, 2014)

It might be possible to create a simulated dynamic effect by using different IR impulses loaded into separate convolution instances and sending different Groups to them depending on velocity levels, but I'm not sure that it would make enough of a difference to try it.
I did learn that you must eq the impulse to keep the boxiness under control, especially if you are using an IR created from the same guitar that was used to create the samples for the instrument. Makes sense, since the resonance of the guitar would be built-in to the samples and would re-enforce those in the IR.
Amazingly, loading an IR made from another guitar made the result sound much better. And very much like the other guitar.


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## MacQ (Feb 4, 2014)

Tracy, it's funny you say that because it's exactly what I thought to do. Actually, probably more useful is taking 5 different buses fed by 5 different sample round-robins, each with its own IR variant. CPU much? LOL!

I've often wondered if there's a standard plot out there for body resonance. For example, if I wanted to take the "cello out of the cello". Not a lot of literature that I've been able to find on determining the fundamental and harmonics. Maybe I should try that tone-linearization plug from Zynaptiq "Unfilter" ... hmm ...


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