What do IRs and Cab Sims actually do?

[rpjazzguitar]

I understand they're supposed to make it sound like you're playing with a certain amp, cab, mic and/or room.

What I'm asking is how they actually do this. Is a cab sim just a fancy EQ profile? If not, what else does it do?

I'm assuming an IR is the result of putting a burst of energy of some kind (white noise?) into something like a guitar amplifier and then measuring the output with a mic somewhere nearby.

The IR is then the mathematical relationship (transform? numerical convolution?) between the impulse (the burst of energy) and the output (what the mic hears).

But, the resulting relationship would seem to be dependent on what aspects you pay attention to when you do the math. Is it just EQ? Or does delay enter into it? Something else?

What is behind this is trying to figure out what I'm missing when I use a powered speaker. I'm doing the listening experiments (and have reported on them ad nauseum) but I'm also trying to understand something about the math.

Thanks.

[John A.]

Older style cabinet emulators are just filters that cut some of the high end off approximately the way a speaker does; some are that + some sort of extra bit of distortion intended to emulate speaker distortion (supposedly what the original SansAmp pedal did).

I/R is different. It stands for "impulse response" and is digital signal processing that replicates what a component or environment does to an input. They're built by comparing a short duration input (impulse) to the output and converting that information into a mathematical function. An I/R profile can be done for anything that has an effect on an input of some kind (e.g., a reverberant room's effect on a sound, an amp's effect on a guitar signal, a speaker's effect on an amp's output). The profile is loaded into a processor (e.g., some sort of guitar effect), and then superimposed on a signal passed through the processor.

[rpjazzguitar]

Older style cabinet emulators are just filters that cut some of the high end off approximately the way a speaker does; some are that + some sort of extra bit of distortion intended to emulate speaker distortion (supposedly what the original SansAmp pedal did).

I/R is different. It stands for "impulse response" and is digital signal processing that replicates what a component or environment does to an input. They're built by comparing a short duration input (impulse) to the output and converting that information into a mathematical function. An I/R profile can be done for anything that has an effect on an input of some kind (e.g., a reverberant room's effect on a sound, an amp's effect on a guitar signal, a speaker's effect on an amp's output). The profile is loaded into a processor (e.g., some sort of guitar effect), and then superimposed on a signal passed through the processor.

John, thanks for this. So, if I understand it, the IR is the "multiplier" (actually, I'd guess it's a numerical convolution) which turns the impulse into the output, mathematically speaking. Can it be broken down into components? That is, can you say it's X amount of EQ and Y amount of delay (maybe stratified by frequency), and Z amount of distortion? Or is it an impenetrable black box?

Behind this is wondering what makes the Henriksen Bud/Blu great. If it's good for vocals, which is claimed, it must be FRFR or close. It has 5 band EQ but no IR. Of course, it has a cabinet, so it doesn't need IR for that. Reportedly, it sounds great, so it doesn't need anything more.

Powered speakers are also FRFR and I recently learned that the Everse 8 has global 7 band EQ and 3 band on each channel. Is there a reason the Bud/Blu should sound better? Why? Everse also has a cabinet. (No, I haven't emerged from the rabbit hole and I'm still digging).

And, an aside. Is it possible to buy something like the Everse 8, but without the battery? Is one of their other models equivalent but without the battery (which I don't need and don't need to carry).

[John A.]

John, thanks for this. So, if I understand it, the IR is the "multiplier" (actually, I'd guess it's a numerical convolution) which turns the impulse into the output, mathematically speaking. Can it be broken down into components? That is, can you say it's X amount of EQ and Y amount of delay (maybe stratified by frequency), and Z amount of distortion? Or is it an impenetrable black box?

Convolution is the right term as I understand it. I guess you could do an impulse response of each element of a system and chain those together, but I don't think that's common. I think the main value of an I/R is it allows the behavior of an entire system to be emulated without having to analyze and reproduce its inner workings (which can be done by other means that afford control over parameters)

Behind this is wondering what makes the Henriksen Bud/Blu great. If it's good for vocals, which is claimed, it must be FRFR or close. It has 5 band EQ but no IR. Of course, it has a cabinet, so it doesn't need IR for that. Reportedly, it sounds great, so it doesn't need anything more.

I think those amps can be either FRFR or somewhat more colored based on how you eq them and whether or not you switch in their tweeter. I prefer other amps, though, so I wouldn't be the one to ask why they sound great.

Powered speakers are also FRFR and I recently learned that the Everse 8 has global 7 band EQ and 3 band on each channel. Is there a reason the Bud/Blu should sound better? Why? Everse also has a cabinet. (No, I haven't emerged from the rabbit hole and I'm still digging).

And, an aside. Is it possible to buy something like the Everse 8, but without the battery? Is one of their other models equivalent but without the battery (which I don't need and don't need to carry).

Sorry, but I have no idea about any of that. I don't use any of that gear.

[woyvel]

I haven't found anything like it that didn't also feature battery power, like the Bose S1Pro+. I bought it primarily for solo acoustic PA but decided to use it with a Boss GX-100 for an FRFR rig component too.

[Spook410]

It is an interesting and kind of complex topic. This guy explains it a lot better than I could..