Impulse Response to make acoustic sound better through electric amp

[sam.spoons]

I have a ZT Lunchbox Junior which is a handy bit of kit, pretty loud and has the capability to be powered from a small Li-Ion battery pack. But it is an electric amp so loads of high mid 'push' to the sound and limited eq. I bought it for busking Gypsy Jazz with a looper and it'll do fine just as it is (think Django's electric period ).

I also have a TC Impulse IR pedal which does a good job of making a piezo pickup sound reasonably natural so I thought, can I make an IR that will make the pickup through the LBJ (it's gotta be called Lyndon hasn't it...) sound something closer to the acoustic sound of the guitar? I know the limited frequency response of 'Lyndon' will mean it can't do as good a job as a decent FRFR box but if I can tame some of the excess mid range and lose the piezo quack I'll be very happy.

How would I go about it though, I'm guessing it'll involve an IR of the amp and playing an IR of the guitar pickup through that to create a new IR of the result but at this point by brain is fried.

[Doug Young]

Some of the IR experts may have better ideas, but I'd think of this as just being wanting to capture an EQ curve that works for you with that amp. I'd record your guitar into a DAW, using an IR you like when recorded (thru a full response system), if you want. Then play that track back thru the amp, and use an EQ in the DAW to tweak the sound to your taste. Then apply that EQ curve to an impulse (you can download raw impulses from online, it's just basically a click). Save the EQd impulse, and then load that into your pedal. That should reproduce the EQ curve you tweaked in the daw.

Another approach would just be an EQ pedal of some sort, or a good preamp with good EQ, that you can use to make the overall sound better. The new ToneDexter, for example has multiple parametric EQs, so you could just create an IR the normal way in ToneDexter, then EQ it to sound good thru your amp - I tend to use a looper for that sort of fine tuning, so I can listen to the amplified guitar with no acoustic bleed, while I'm tweaking. The Baggs Voiceprint could also be used the same way. Or add a good parametric of graphical EQ to your TC pedal.

[jonfields45]

Rather then send the pickup into the IR calculator, mic the guitar, and mic the amp. Try to get them acoustically isolated. Send me the amp recording left, and the guitar mic recording right in a .wav file, and lets see what we can do. They need to be recorded at the same time. 30 seconds of open position strumming is more than enough.

Since my approach is just the math, not any equalization assuming anything to make it sound nice, it just might work.

The pickup on the guitar should not be magnetic for it to work regardless...

[sam.spoons]

Thanks gents, I have a ToneDexter mk1 which is great and bought the TC Impulse as a cheaper, smaller alternative for open mic nights and maybe a bit of busking.

As I said the LBJ doesn't have the frequency response to do a proper job but applying a 'smile curve' to an existing IR would probably get me close enough.

Jon, thanks for the offer, I may take you up on it, I have downloaded a few of the IRs from your site and loaded them into the Impulse pedal. Haven't had chance to try them yet though. I plan to use your method to convert a couple of ToneDexter wavemaps into IRs too for use with my other acoustic amps.

I guess I'm trying to work out how to create a sort of 'inverse IR' to to reduce the amp sound. Having made the recordings maybe I could use the TD to do what you are suggesting?

[Doug Young]

Originally Posted by sam.spoons

I guess I'm trying to work out how to create a sort of 'inverse IR' to to reduce the amp sound.

I don't really see this as an IR problem. The IR's great as a way to capture something complex, the resonance of the guitar and so on. And I don't see why it couldn't be used to include and "undo" the influence of an amp/speaker, but it doesn't seem all that necessary to me. (tho certainly an interesting experiment) Plain old EQ should take care of the amp (within limits), and is easier to control and dial in to your taste. Use the IRs to do the hard job of getting the quack out of your pickup, then just EQ the amp to taste. If you want to simplify your setup by capturing that EQ curve in an IR, that's ok, but it won't be adjustable on the gig, which often changes things radically.

What I've done about sound thru my amps and PA speakers, is set them up, play thru a looper so I'm not fooling myself with any direct acoustic sound from the guitar, and EQ till it sounds good. Then save that EQ as a preset, as a starting point, knowing I'll need to tweak a bit on a gig. Of course, if I have a gig where I'm playing thru an unknown house system (most of the time), the only choice is to try to adjust on the fly.

[shufflebeat]

Originally Posted by jonfields45

Rather then send the pickup into the IR calculator, mic the guitar, and mic the amp.

Please try this - I’d be very interested in how it works out. It may sound awful but knowing would be good.

I may do it as well but time is short at the minute. By my basic maths this is now a three way convolution - *pickup/mic/amp. Could be very interesting.

*possibly:
pickup/guitar = IR1
IR1/amp = IR2.
IR1/IR2 = IR3 - (pickup in/amp out)

[jonfields45]

As long as the amp is linear, that means not generating harmonic distortion, then what I am proposing can work. In this case it will generate an IR attempting to make the pickup to amp to speaker sound like the mic’ed guitar. That in use the pedal is before the amp is irrelevant as the order of linear transformation is unimportant.

I am not blowing smoke that my generator just prunes noise from the samples and is simply the raw Fourier arithmetic. That is the right approach for this experiment. ToneDexter is clearly a better approach for the conventional case, as you don’t need to know how to embellish the raw math with EQ, but that EQ might not be appropriate for this unusual experiment.

I’m a huge ToneDexter fan. You should try it too.