Capturing Acoustic Body IRs

gdgross

gdgross

Experienced
Hey guys -

Is there a good method for capturing Impulse responses for acoustic instrument bodies?

At one point in my history I used Logics' IR capture to take impulse responses of the D-Tar Mama Bear, but hw would one go about it with a real acoustic instrument? Bang on the body and record the DI signal?

I know some IRs can be calculated using a swept sine wave and convolution, but it seems this isn't really that feasible for a real instrument that only takes mechanical inputs instead of electrical. Any ideas on how those acoustic body responses floating around here were taken?

Thanks!!
 
I've never tried it myself, but I think you'd do it by capturing the guitar's response to an impulse. Tap on it, and record the sound you get.
 
My understanding is they're tone matches. For example, record some chords by using the piezo on acoustic and tone match this to the same chords captured by a mic.
 
An IR is always going from a source to a target - With an acoustic, you often match the signal from the on-board pickup to a mic'ed signal.

It is possible to just hit the bridge of the acoustic (softly) with something like a rubber hammer while muting the strings while recording with both a microphone and the on-board pickup. Then you can use something like Voxengo Deconvolver to extract the IR from that - There is a website out there describing this process, and they have a neat little program for the process - But I cannot find it right now.

Anyway, as @2112 writes, most acoustic impulse responses are made as tone matches. Either in the AxeFX or in a DAW with a match EQ plugin. I use Melda Productions MfreeformEQ for this. Once you have done the EQ matching, the IR can be extracted using a sine sweep and Voxengo Deconvolver. I can make a video about this process, if you are interested.
 
Thanks guys. I did use some deconvolution in the past when I took those mama bear IRs a long time ago. But now that I've kind of settled into my "keeper" acoustic instruments, i think I'd like to capture some IRs of all of them, as I usually run them as "specialty" instruments alongside my electric guitar through the ax8.

So basically, there's two methods sounds like, one more used in practicality: you record the DI and mic'd signal, do. an eq match, and then sweep a sine through the matched eq and deconvolve that into an impulse response. Simple enough I guess! I think logics IR utility had a deconvolver which I used last time. Since I don't have logic any longer, I'll have to check out voxengo as you mentioned or some other deconvolver.

I suppose once in set up to record I may as well mute the strings, tap on the bridge, and do some real IR captures anyway, as it won't take much more time. Then I can compare and see which yields the better results. I have a feeling the banjo IR captured with this method will sound funny though, but I guess I'll find out!!

Thanks!!!
 
I actually made a video tonight, but somehow, I didn't record my voice, so it's useless. I will try again tomorrow.
 
Cool thread, I will have to dig a little deeper into it.

I almost managed to make a video yesterday. I just need to record a little example, and I need to do some editing. It might be up tonight (it is morning here now)

There are basically two issues when doing this 1) I actually find it quite difficult to get a really good recording of my acoustic guitar. I just did some acoustic regulation of my recording room, and that helped a lot, but otherwise it has been really difficult. 2) Finding a good plugin to use for the Match EQ. I haven't found any free ones. Both Ozone and FabFilter will do it, but they are very expensive. I use Melda MFreeFormEqualizer, I like it a lot and it is only €50. Another is Voxengo CurveEQ. The latter one runs in a demo version that is actually sufficient for our needs.
 
I am quite happy with the sound of my acoustic going into the AX8 but I don't use it as often as I should. I use the AX8 mostly with my electrics. For live or recording I still far prefer the sound of a mic on an acoustic to any combination of the pickup. The AX8 gets really close to what I have in my head. I guess I should use it w acoustic more. Strangely enough, I go heavy on effects with my electric, but basically dry with acoustic.
 
Smittefar said:
I almost managed to make a video yesterday. I just need to record a little example, and I need to do some editing. It might be up tonight (it is morning here now)
Click to expand...
It will be up tonight. It needed a bit more editing than I could finish last night.
 
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