Testing IRs for the first time

**Jim Soloway** · 08-10-2020, 03:47 PM

I've been trying IR's for the first time this afternoon. I recorded this in Reaper with the Kuassa Amplifikation Lite Amp sim with a free test IR. So far pretty much all the IR's I've found are based on big rock cabs but it's a start. Compared to my direct tracks I think it sounds pretty good.

**Skip Ellis** · 08-10-2020, 03:57 PM

Real nice, Jim! Not sure what an IR is. I'm clueless about sims, etc. I'm so old school that I think any amp that doesn't have a master volume and makes my guitar louder is a good amp. I've pretty much settled on my Quilter 101R and Ear Candy Mr Watts clone (8"). If I need to peel paint off the walls I still have my Evans RE200 but doubt that'll happen any more. Congrats on the new house!!

**Jim Soloway** · 08-10-2020, 04:02 PM

Originally Posted by Skip Ellis

Real nice, Jim! Not sure what an IR is. I'm clueless about sims, etc. I'm so old school that I think any amp that doesn't have a master volume and makes my guitar louder is a good amp. I've pretty much settled on my Quilter 101R and Ear Candy Mr Watts clone (8"). If I need to peel paint off the walls I still have my Evans RE200 but doubt that'll happen any more. Congrats on the new house!!

Thanks. An IR is an "Impulse Response". As I understand it, it's a sample of the response of a specific speaker response including the speaker, the cab, the mic and mic placement and the room. They're considered a very big deal in the amp modeling universe. In some ways a bigger deal than the amp models themselves. From what I've seen in my testing today, some of that may well be true. They do have a really big impact on the final sound.

BTW, the Strymon Iridium uses IR's for their speaker emulation and one of the big features is that you can replace the IR's with other IR files so the cab simulations can all be custominzed.

**TedBPhx** · 08-10-2020, 04:34 PM

The Fender ToneMasters use an IR to model their reverb for both the cab and the XLR out mic emulation. Of the 4 core DSP processor 3 out of 4 are devoted to those IRs 2 for the main and 1 for the XLR.

**wzpgsr** · 08-10-2020, 06:19 PM

Testing IRs is one of the deepest gear rabbit holes I’ve fallen into. Holler when you want someone to throw you a rope.

**Skip Ellis** · 08-10-2020, 06:28 PM

Doesn't matter what I play, I sound like me and that's the way I like it, but to each his own........

**Jim Soloway** · 08-10-2020, 06:39 PM

Originally Posted by Skip Ellis

Doesn't matter what I play, I sound like me and that's the way I like it, but to each his own........

Right now I have nothing to play through so I'm mostly playing my little Emerald X7 unpluged. I'm probably not going to have any kind of amplification until after September 10 so it's a good time to muck around with stuff like this.

**dconeill** · 08-10-2020, 11:42 PM

Back in the 80s when I was taking a run at being a geophysicist, we used impulse responses as a way to build models of what a seismic signal would look like when recorded by a particular seismic instrument.

The idea is this: you hit a seismic recording instrument, analogous to a microphone, with an impulse (i.e., no signal, then suddenly a signal, typically only one digital sample in duration, then no signal). You record the instrument's output. This output is the "impulse response". Once you had that, you could model an input signal, e.g. a small or large earthquake, or a mine blast, or a nuclear explosion, pass it through the instrument's impulse response, and look at the output. You could use this to see what a particular kind of seismic event would look like through a particular instrument. The instrument itself sensed ground motion at its location and recorded the result, as affected by the instrument, as a seismogram.

Of course this is an oversimplified description. No physical device that I've ever heard of can reproduce an impulse exactly - there are always time delays, inertial limits on how fast a detector at rest can be set into motion, response peculiarities in the instrument, and so on. But it's a place to start. If you knew the impulse response of a particular seismometer, you could back out the response of the instrument and end up with (more or less) what the ground was doing at the location of the instrument. You could even put that "deconvolved" signal through another impulse response to see what the same ground motion would look like through a different instrument.

Something similar is done with IRs in amp simulations. You put an impulse into a speaker and record what comes out. It takes the speaker some amount of time to get into motion when it first receives the input signal, it takes the speaker some amount of time to stop moving once the signal stops, the frequency response of the speaker comes into play to color what comes out given a particular input, and so on. The goal is to produce, from a mathematical/digital model, something similar to what happens with a real signal going into a real speaker.

Now keep in mind that I was unable to make a career of geophysics, so my explanation might be incorrect. But for what it's worth, that's my general understanding of IRs in amp sims.

**feet** · 08-11-2020, 12:34 AM

That's a much fancier explanation than I can give, but it helps to think of it as an eq curve. Every speaker and cab all have it's own sound, and an ir is representing that sound and applying it as an eq curve. If it helps, consider analog cab emulation, like a Rivera rock crusher recording or a suhr ace. A digital ir is doing that, in a nutshell.

I prefer something that allows you to select and "move" digital microphones around on these digital cabinets, but that's a more expensive feature. I used to have single irs before and I hated flipping through them and auditioning them. The best sounds always came from being able to place a couple of mics and then bring up a little bit of the room mic, them a little reverb on top of that. Oftentimes, people are unhappy with an ir because it's the sound of a single mic right on the grill, which isn't what we hear in the room. What your ears hear and what a mic hears is very different and it takes time to get your head around that.

**AKA** · 08-11-2020, 02:00 AM

Sounds fantastic - the IR sim and the playing!

**dconeill** · 08-11-2020, 08:38 AM

Originally Posted by feet

... it helps to think of it as an eq curve. Every speaker and cab all have it's own sound, and an ir is representing that sound and applying it as an eq curve. ...

This isn't wrong, but thinking of an IR as only a frequency response curve is incomplete. There are time-related elements of response that are captured in an IR that are not present in an EQ curve.

**thpm** · 08-11-2020, 10:58 AM

Two thoughts, based on my experience:

- In the beginning, I think one naturally is inclined to stick to what one knows, and also do the ‘right’ thing: only try Fender amp sims with Fender cabs, Vox with Vox, etc. — but it has really been enlightening for me to drop that and not get hung up on “big rock cabs”, brands or what one knows from real hardware. I've been having pleasing results with totally ‘insensible’ combinations. That's the great thing about IRs. I mean I have zero desire whatsoever to haul a 4x12 cab around, ever, and that's why I never even tried to plug into a real one. But a 4x12 IR is the same weight as a 1x8… (;

- It's a rabbit hole and it's easy to get lost… but you also learn a lot. For example how much of the “Fender-Sound” comes from speaker and cab, not the amp.

For further experiments:

Big free pack, includes JC-120, Fender Twin and Vibrolux, and lots of others:
Seacow cabs Christmas IR Pack – Seacow Cabs Impulses

and if you like the Poly, Polytone 1x12 (Mini Brute II), and 1x15, 2x8 IRs