How to Create an Impulse Response for ʻUkulele or Guitar

Plugging in a piezo ʻukulele pickup has always been a compromise. But can impulse responses help the situation?

Good as a piezo might be, there’s always a trade off in sound. In a head-to-head contest, a microphone will always sound better. The pickup element just can’t reproduce the same frequencies in a musical way.

With a technology called impulse responses (IRs for short), you can now create an EQ curve that mimics the frequency response of, well, ANYTHING!

The most obvious use of this would be to EQ a piezo to make your ʻukulele sound like it’s playing through a microphone.

What the Heck is an IR?

In layman’s terms, an impulse response is a snapshot of an EQ curve that you store in a little audio file. It allows you to capture the sound of specific things – instruments, rooms, amps, etc… When you apply this EQ curve to another sound, you’re creating the illusion that you’re playing the IR instrument, room or amp.

The IR EQ can be as detailed as your equipment will provide, allowing you to really get an accurate rendering of the source material – much more so than you ever could before, even with a fancy standard EQ.

For instance, you could use an IR to recreate the sound of an elephant in a room – literally. You’d record the sound of the room with a mic (by playing a track through a speaker or something similar). Then you’d bring an elephant into the room and – assuming it was one of those silent elephant types – record the exact same thing again.

Using some fancy software you’d analyze the discrepancies between the two audio files and export the difference in EQ as an impulse response. This could be then loaded into an IR-reading device and used to create the sound of an elephant in a room anywhere, even if you don’t have an elephant handy at your studio.

Products like the Fishman Aura series and others have leveraged impulse response technology for a while now to create better live guitar sounds. Unfortunately, this has excluded players of more obscure instruments since the presets are made by Fishman for Fishman products. If there isn’t a market for it, you don’t get an IR.

Times are changing, of course, but if you don’t want to wait, you can do it yourself.

New IR Options

With the advent of the Audio Sprockets ToneDexter, IR technology came back onto my radar. It also made the technology the most accessible its been to the average Joe.

This device does the hard part of creating an impulse response for you. You simply plug in your favorite mic alongside your instrument pickup and the pedal creates an IR of the difference. That way when you play with just your pickup, it’s altered to sound like the microphone. Very cool, but expensive for this one purpose.

Recently I upgraded my hodge-podge pedalboard to the new Line 6 HX Stomp. It’s compact and has all the effect options I could ever need. Yes, it’s expensive, but no more so than the collection of individual pedals it replaces.

Bonus: the HX Stomp allows you to stick IRs in your signal chain.

I knew this was valuable to creating a better live ʻukulele sound, but it took me a while to figure out how to implement it. After several waves of research, I figured it out. And it’s not as hard as it seems once you know what you need and how to do it.

What it Sounds Like

Before I go any further, let me convince you why this is worth exploring.

Without IR:

With IR:

I couldn’t believe my ears when I first loaded these up. They’re a little flat recorded into the computer, but the potential for sound polishing is huge! This was only my first try too!

This is with the IR mixed at about 60%. 100% is too bright, but combining the two signals gives you the best of both worlds.

Now that you want to play with these too, let me show you have it’s done.

The following applies to any instrument you want to make an IR for. When doing my research, there seemed to be a lack of easy solutions in general so perhaps this will be useful for a guitarist, keyboardist, or banjo player down the road.

How to Make an IR

You need:

  • A DAW program of some kind that will run 3rd party plugins (I use Cubase Artist 8)
  • A match EQ plugin of some type – MFreeformEqualizer by Melda Production ($45~ with my referral code: MELDA2762597) does the job great and, it turns out, will render the IR for you
  • A source file that you want to replicate
  • A target file that you want to sound like the source file
I’m sure there are many ways to do this, but MFreeformEqualizer worked fine for me and was way easier than I was expecting. If you’re going down the IR rabbit hole you’ll be shelling out some bucks regardless, so for me, $45 felt like a deal.

Source and Target Files

The whole idea of creating an impulse response like this for ʻukulele is to make up the difference between miked and plugged in sounds. To do this you need to have a start and end reference recordings.

You could, theoretically, use someone else’s ʻukulele recording and match it to your plugged in sound, but for me the whole idea is to get my great-sounding ʻukulele sounding like itself through a PA, not to copy someone else’s sound.

I didn’t even create new recordings for this IR. I just used my rhythm ʻukulele part from a song off of my album, If Only.

The main point is that you have a recording of your ʻukulele using a mic that you like (each mic sounds different and will create a different IR) AND also the pickup.

For me, to get the most sterile IR environment possible, it makes sense to record the mic and pickup simultaneously while playing something typical of my style. I had a whole album worth of material to work from with separate mic and DI tracks from the same take, but you probably only need around 30 seconds to capture the IR.

If you’re not sure about recording your ʻukulele, follow the link and do your homework. This is a project that builds upon recording and DAW skills and should probably not be your first try at tracking your ʻukulele.

Now you should have two tracks in your DAW: one of the miked ʻukulele and one of the pickup.

This next bit is the fun part.

MFreeformEqualizer has two options for capturing the source EQ curve: sidechain and audio file. I don’t have sidechain capabilities in Cubase so I was grateful for the audio file option.

Using the sidechain allows you to work without ever leaving your DAW. It’s not crazy hard, but you’ve got to figure it out. Here’s some sidechain reading on Sound On Sound.

To go the audio file route, bounce a soloed render of your microphone track out of your DAW. Then load MFreeformEqualizer onto the pickup track. This is where we’re going to superimpose the miked uke IR.

In the MFreeformEqualizer look for the “AUTOMATIC EQ” section at the bottom of the window. Click the arrow/window button to expand it, if needed.

Now click the drop down on the right side of the red “ANALYSE source” button:

using mfreeformequalizer to create irs

Select “Analyse audio files.”

analyse audio files mfreformeq

Now choose the microphone render you just exported (hope you put it somewhere easy to remember!).

how to select track analyse mfreeformeq

MFreeformEqualizer will quickly analyze the track and create and EQ curve for it. Like so:

eq curve in mfreeformequalizer

To get the most detailed IR possible, you can pull the smoothness knob down to 0. This creates more points along the EQ curve and will look more saw-toothy.

smoothness at 0 mfreeformeq

Default output should be “0” and default range should be “+24.00db”. In the tutorial I watched, the guy recommended clicking the “minimum phase” option for the best IRs.

Now we’re going to overlap the EQ of the two tracks. Press the green “ANALYSE target” button and press play in your DAW. (Remember the EQ plugin should be loaded on the DI pickup track!)

analyse target mfreeformeq

The plugin will analyze the playback of the track and create a new EQ curve that will hop around for a bit. Let it play until the curve settles down and stops moving as much. Then pause the playback.

Click the “ANALYSE target” button again to finish. Now you’ll see both EQ curves. The microphone track is in red, the pickup track is in green. You should see some discrepancies. If not, you might have your tracks mixed up and you just analyzed two versions of the same track.

source and target eq curves mfreeformequalizer

To see the discrepancy between the two tracks, just press the “EQUALIZE” green/red button. (I imagine you can reverse your track inputs and click the “SEPARATE” button here.)

These are the EQ changes MFreeformEqualizer will make to the pickup track to make it act like the microphone. At this point you can play back the pickup track (be sure to solo it) and hear what the IR will basically sound like on your plugged-in sound.

target and source equalization

The last step is to click “Save IR” above the EQ window. Locate a folder and name your IR and you’re set!

saving ir mfreeformeq

The IR saves as a .wav file that seems to be optimized for most applications. From here you’re on your own to figure out how to get the IR onto your device. It was really easy with the HX Stomp.

IR Possibilities

In addition to the very straight-ahead Neumann KM184 mic IR I made, I also took some content from other source tracks.

One was another mic sound that I liked from my album. This particular take didn’t have a DI track as well so I rendered it against the plugged-in track from the first IR. Surprisingly, this one doesn’t sound very good.

Here it is with the IR at 100%. There are some serious phase issues going on:

I imagine that when you’re trying to create the highest-quality acoustic IR possible, it really helps to reference tracks from the same take. (I.e. one track for the mic, one for the pickup, recorded simultaneously.)

Another I did was of a fuzz electric guitar sound from a song I dig. The trick to using already recorded songs is finding a snippet where the guitar (or other instrument) is playing by itself. Not everything will give you a clean shot at an EQ curve, but this track happened to have just guitar in the intro.

This turned out to be a pretty radical EQ curve, but I thought it was a huge upgrade from the normal fizzy distortion tones you usually get with a piezo equipped uke. It sounded more guitar-like and alive. Like you’d expect a steel-string uke to sound.

This was a 50-50 mix, I think. Again, too much and it can be overwhelming. There’s good thing about both.

By Brad Bordessa

I’m an ‘ukulele artist from Honoka’a, Hawai’i, where I run this site from a little plantation house in the jungle. I’ve taught workshops internationally, made Herb Ohta Jr. laugh until he cried, and once borrowed a uke to jam with HAPA onstage in my boardshorts. More about me

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