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Recording acoustic guitar IR’s for improving piezo pickup sound?
Hey I’ve recently discovered how much an acoustic guitar IR improves the sound I’m getting out of a piezo contact pickup but I’m wondering how to create my own...
There’s tons of free cabinet IR’s out there, and I did find one set modeling an acoustic Taylor that is nice, but I’d love to try recording and using my own. I play a unique instrument called a Mohan Veena that is REALLY lost into a contact mic and while that Taylor IR helps immensely (super happy to have discovered this) I think it could really benefit from making my own IR for it.
I’ve found plenty of resources for doing this on PC’s but can’t find anything for iOS...
For now I’ve been using THAKFNAR for loading IR’s and I see in the standalone version the ability to record but it’s a bit mysterious to me how to create an IR to model the body of my instrument. Any suggestions/comments from some of you tone gurus out there would be much appreciated!
Thanks
Comments
Would love to hear your Mohan Veena in action! Big fan of Pandit Debashish Bhattacharya,, Hindustani slide guitar guru. Try using the Fiddlicator app, there are IRs in that for cello and violin
Stating the obvious here: the piezo picks up a tiny local movement of the wood, while you hear the full guitar top swinging (coupled to air) by your ears.
The latter is a dynamic process (depending on intensity, speed and way of string hit) and very unique for any particular instrument.
The piezo signal isn't a proper excitation anyway because it represents the wood's response and not the pure string action.
That's what makes any kind of 'modelling' difficult.
There are in fact guitars, that fully emulate the top and body response (iirc by complex physical modelling), but they sound extremely limited (boring) if compared to a real guitar.
You may try to record the guitar's response to a very short hit of damped strings, approximating a broadband impluse excitation.
(no idea what comes out of this, but it's similiar to the shot method used for room IRs).
Recording an IR is rather easy but recording it in a way that you get a good-sounding IR is another thing.
A little bit of theory: Processing your signal with Thafknar and an IR loaded is in fact the signal convolution of the IR with your input signal. Simply said, imagine the sound frequency spectrum of the IR and the sound frequency spectrum of your input signal and then multiply both. Where the frequencies exist in both, they are retained and where there's a frequency that only exists in one of the signals, the result is low or zero.
The ideal source sound to record an IR is a very short impulse with very high energy, recorded with a microphone that can capture the sound pressure level without distortion.
Some use a signal gun, a bursting toy balloon is another option.
Place one microphone (or better two at different positions) inside the guitar body, set the recording level manually to prevent overload and record the balloon bursting in front of the guitar body hole.
If you don't like the resulting IR files whatever you try, then also consider editing your IR recordings with a wave editor and add equalization and a better level envelope to the file(s). A lot can be fixed this way.
Keep in mind that an IR of your guitar will act like an eq and won’t do a lot of the things that guitar modelers do. What people often use for the impulse for getting guitar and violin IRS is to tap on the instrument.
Experiment a lot with where you tap (use your fingernail or something hard to strike the instrument) and where you place the microphone.
The Fiddlicator IR app was originally intended to help electric violin players get a more natural sound.
Hey forgot to say thanks for suggestions guys. I put this on hold for a bit but will try soon and see what kind of results I can come up with...
I found someone here (https://liveukulele.com/lessons/plug-in/impulse-response-tutorial/) talking about making IR’s for their ukulele using some EQ matching software...any ideas about that method for iOS?
My instrument has “f-style” holes so placing a typical mic inside as @rs2000 suggested is not really an option...
@Tickletiger said:
If I can get it together I plan on posting a video pretty soon of some looping I’ve been doing with my Veena. And yeah Bhattacharya is a nice player, but I have a bit of Guruji bias of course for my teacher, Dr. Sanjay Verma from Varanasi, he’s got a few short videos taken of him on YouTube but isn’t very well known. If interested I could send you some recordings.
I use acoustic ir’s when I have to track acoustics on live shows where miking them up is not practical. They make a huge difference, I really don’t enjoy the sound of an acoustic DI on a recording.
Are these IRs you made or purchased?
I found them online for free. I have a bunch of questions to answer today about various things so I’ll see if I can find where I got them when I go downstairs in a little while. If nothing else I can dropbox them to you, I don’t believe any are license restricted. 3 sigma has some good ones for purchase, but i don’t have any of the acoustic guitar ones. I have a few of the upright bass sets that I’ve tried with my electric upright bass and they are cool.
Cool, tx
Fascinating thread!
Very interesting approach! Because you are trying to fake what happens at the piezo pickup and translate into what happens with the body resonating and getting recorded by mics, it seems like it would be the most accurate (though not necessarily the most pleasing?) way to translate that would be to tap near the piezo pickup, by the bridge.
@rs2000 yes, I’d read too about using a starter pistol or balloon popping to fake what would happen if you were to play a single sample of audio into a physical space. Love the idea of someone walking in on you stuffing a balloon in your guitar so you can pop it and record the sound!
I have used the Logic Pro impulse response utility, which is fantastic, if you have access to a Mac. It plays a sweep, rather than a pop, out of your speaker, and then records your mics in the space, then does all this math to “deconvolve” the sweep, into what a perfect, one sample pop sounds like, in that space. With this scenario, rather than a speaker in the guitar, it could be good to use a tactile transducer, it’s like a speaker, but you attach it to surfaces and it makes them vibrate, it makes like, a table or wall into a speaker. I’d done some fun science projects playing electric guitar into an acoustic guitar body, sounded like a funky, bluesy arch top.
I think in the OP’s scenario you would want to remove the strings or muffle them when making the impulse response, so they wouldn’t resonate. You already have sympathetic resonance in the strings, in the piezo signal you are transforming, you wouldn’t typically want to add open strings resonating on their own, like a sitar.
@Processaurus Oh my, been using Logic for decades and didn't even know the IR utility could do deconvolution! Thanks for the hint!!
You're right about the strings sympatethic resonance if your source signal is a guitar already, I was rather coming from my own experiments with acoustic guitar IRs applied to synthetic (pluck) sounds. In that case, including the strings can be desirable.
Lots of fields for fun experimentation while in quarantine 😎
So cool I had the same idea a while ago but forgot about it. Thanks for starting this thread!
Would be cool to get practical here!
Would be great to find out:
What IR app works best (low CPU / latency / AUv3?)?
What IRs sound nice and where to get them?
Or anyone got nice EQ curves / presets? (probably best for CPU / latency)
Any before / after sound examples?
Looking forward to getting into this and working out some practical solutions!
I don’t think that there is an IR app more efficient than THAFKNAR. It is also inexpensive for the AU IAP. If I recall, you can use IRs in the app without an IAP. The dev is also responsive. It’s u.i. is not fancy but the software is solid.
Oooh there's a lot going on in these Mohan Veenas...all built on resonance and sympathetic vibrations. Take a look:
You reckon a ukelele IR will handle that complexity ... stuff going everywhere... need a web to catch it all.
That's a lot to ask of a single piezo pick-up -and I suspect that you might want to try using a few - to capture the richness of the sound and its various components - a much more complex source and signal.... get three or four and run them through a little passive mixer/to balance 'em up.
Not sure how much room you've got on the Veena but the position of a piezo is absolutely critical to sound quality and timbre - so is the quality of the contact - both the pressure and area. You can in fact "tune" them. A normal guitar arrangement might not suit the character of the sound... I use three on a cello - one under the bridge (trebly and brittle), one onto the back (deep and boomy) at the fattest bit and one under the fingerboard ( percussive) ... _
Cheap as chips - so get experimenting.
But I'd have a go with a decent hot single coil magnetic pick-up myself ... give it that authentic Mumbai swampy blues twang. Great sound.
Cool, I’d heard about that ability of Logic Pro on some other threads but was really wondering if there’s anything like this for iOS at this point? No Mac here and given the whole quarantine thing accessing someone else’s is a bit off limits... And actually I’m up in a cabin in the Himalayan foothills so not much access to anything technical anyways!
Nice idea to try out with the tactile transducer, look forward to experimenting with this when I get outta here eventually. A while back I saw a crowdfunding campaign for an acoustic guitar that used this idea to apply fx to itself and amplify out the body...not sure what came of that but I thought it was a cool idea.
Yeah that is the difficulty here! And actually mine is a bit more complex than Harry Manx’s. He’s got this Vishwa Mohan Bhatt style with many chicari (drone) strings and I’ve got a few more playable strings (5) including an octave lower bass string, and I’ve put a jiwari (sitar bridge) under some of the playable strings to give it extra Indian twang, comes out super rich for the bass strings.
I mentioned the reference to the site with the ukulele IR not for their use but to ask about the guy’s method. Instead of recording a short burst and loading it up it seems he uses some sort of EQ matching software to create IR’s out of the difference that’s recorded by the mic vs a piezo...didn’t fully understand but seemed interesting. Again wondering about iOS abilities with this method.
I’ve been using these Taylor IR’s found from this forum thread:
https://forum.fractalaudio.com/threads/taylor-acoustic-irs.117476/
I’ll try to record a with and without example later if I get around to it. They make a huge difference on their own but when run through an amp sim do strange things coming out the other side...
Probably a good idea to try using multiples. I have experimented with different placements and you’re right it makes a huge difference, but hadn’t tried multiples, will need a little passive mixer though, which as mentioned above is not possible for me till the dust settles...
As of now I use this one from Zeppelin Labs https://zeppelindesignlabs.com/product/cortado-balanced-piezo-contact-mic/ with it’s own matched impedance phantom powered system which does help a lot, but still is of course a piezo at heart and I kind of accepted the thin sound from the pickup, hence my journey into IR’s! I primarily am using it for some experimental acoustic/electronic looping stuff I’m working on so a really clean sound was never that important, I figured if I want the acoustic sound for when playing Hindustani music I’ll just play it acoustically, or into a mic...but this IR thing got me trying for clean again to get more of the richness of the instrument itself.
I am curious about using a magnetic coil pickup. Looking at some videos it looks like Manx does this with his Veena, and it comes out sounding great...another thing to try
They're all pretty much the same really just on the physics of it but piezos don't have to be twangy and brittle ... bass response is very much improved by exerting pressure on the crystals - little plastic clamps- even clothes pegs... but grab it on hard. Sticking a couple of cheap piezos under the feet of a cello bridge for example can give you a deep meaty sound - serious pressure. Same with small pickups under individual strings on a guitar bridge - tunable with the right kit.
Manks looks like he's using a slim profile jazz pick-up - very thin( designed for archtop guitars) - as you can see in that screen clip above...and he's got it up on two little blocks ... so the sympathetic strings actually run under the pick-up. I'd be keen to see that through a phase meter - cancellations all over the place I'd suspect.
Can't see any other source purely for the sympathetic strings - but it'd give you a very flexible instrument - dial up how much Hindu Hop you want in your bottleneck blues. Specially if you've got one of those gourd resonators up the neck ... that's where I'd clamp a decent piezo - it'd be chaos in there!
Be a bucket of fun playing with these complex interactions ... throwing that resonance through delay units and the like... a tardis of an instrument - take you anywhere. Like to hear some when you've got it running to your satisfaction.
The piezo pickups need a very high impedance input, like over 1megaohm if that makes sense. Usually a special preamp. Or if there isn’t one, a guitar input, or buffered guitar pedal (like Boss), rather than a mixer input/line input. Regular line input is low, like 10k ohms, and it affects piezo sound by losing bass response. Opposite of what happens when you plug a magnetic (electric guitar) pickup into a low impedance input, where the tone is bad because the treble gets cut.
I've gone down the rabbit hole of acoustic guitar IRs after having looked at Tonedexter, LR Baggs Voiceprint, etc. Anyone find any new resources since last spring? Here's something I found that looks interesting:
http://acousticir.free.fr/spip.php?rubrique2
https://www.3sigmaaudio.com/
I’ve tried a bunch of the commercially available IRs for acoustic guitar, e.g. Fishman aura, 3sigma etc., and haven’t gotten good results from any of them.
Here’s a sketch of what’s worked a lot better for me. Record a timbrally representative sample of your instrument (something like bar chords chromatically up the neck…) tracking both the acoustic sound and the pickup sound. Then run a match eq with the pickup sound as the source and the acoustic sound as the target. I use Logic‘s match eq for this but you could do it on iOS with fabfilter pro Q3. (You won’t get quite as much detail with pro Q3, but it’s pretty good…) Then run a single sample spike through the resulting eq to generate an IR. Presto! – best electroacoustic sound I’ve ever had…
This belongs in a home recording wiki or an audiob.us wiki on the topic of making IR’s.
I made IR’s of toilet flushes and vacuum cleaners but this exposes how to make a targeted IR based on a spectrum and not a wave file.
What’s a good tool fir that “impulse”? A wave file or an app?
IR stands for impulse response so I wasn’t making IR’s but something like a FR or VR.
Hand clapping in a room works
Not precisely on topic but if you have the app, MixBox can help improve the piezo sound. Also, this pedal works surprisingly well https://www.boss.info/us/products/ad-2/
This website is where I ended up... and found a solution. From links in here you can download free/donationware open source software (works on a Mac) that compares your mic'd versus piezo sound to create an IR which you can use in an IR loader (I use Thafknar on iOS). The website has a ton of info with tutorials to help. Also a crazy long forum post detailing how the guy created his IR software. It's a lot to dig through, but there are some diamonds in there. I'm currently revisiting it all again before I record a new "final" IR for my rig.
I got the Martin D45 IRs and they do improve the sound of my piezo-equipped acoustic (which is an Epiphone J200, not a Martin, but hey).