IR's - what are they?

[tonyclaret]

I know this may make me sound like a dumb donkey, but so be it.

Could someone explain the purpose and use, functionality?

I've noticed a few pedal units with the feature and I haven't the foggiest of what it actually means when it's says you can load IR's. 

Load from where? Is there a website with a million pre-loaded sounds? Do you have create them from scratch?

See I'm totally confused.

Thanks 🤔

Edited August 30, 2018 by tonyclaret

[dannybuoy]

It stands for Impulse Response. Commonly used for cab sims and reverb modellers (to simulate the sound of a specific room), but most pedals you will see would be talking about cab sims.

If you feed a white noise signal that contains an equal spread of all frequencies into a cab, then measure what comes out the other end, you end up with a specific EQ curve for that cab. That can then be used to apply a cab sim via digital processing, and you can download a ton of IRs from the web, e.g. one for an Ampeg 8x10.

It's a bit more complicated than a simple EQ curve though as it takes time into the equation as well, but that's the general gist of it!

[Tech21NYC]

It's often called a cab or speaker sim, but in reality it's the sound of the speaker as captured through various microphones at different positions. Like a close mic'd SM57 off axis or an AKG at a distance of 6" on the cap edge etc. The IR's can very accurately represent the EQ curve as captured through various mic's. They can't capture compression or distortion artifacts though. They are very popular for lead guitar because many times in the studio more than one microphone will be used to capture the tone. They are less popular with bass since bass is often DI'd or a composite sound of a DI and a mic'd cab. Mic'ing a bass cab with stereo room mic's would be kind of pointless for most applications. You also have to convert the analog signal to digital to use them. With bass you could go parallel and use your DI sound and also feed the signal to an impulse response etc.  

Edited September 6, 2018 by Tech21NYC

[Dood]

2 minutes ago, Tech21NYC said:

It's often called a cab or speaker sim, but in reality it's the sound of the speaker as captured through various microphones at different positions. Like a close mic'd SM57 off axis or an AKG at a distance of 6" on the cap edge etc. The IR's can very accurately represent the EQ curve as captured through various mic's. They can't capture compression or distortion artifacts though. They are very popular for lead guitar because many times in the studio more than one microphone will be used to capture the tone. They are less popular with bass since bass is often DI'd or a composite sound of a DI and a mic'd cab. Mic'ing a bass cab with stereo room mic's would be kind of pointless for most applications. You also have to convert the analog signal to digital to use them. With bass you could go parallel and use your DI sound and also feed the signal to an impulse response. 

I'd venture that with the advent of the 'new wave' of digital processors such as Positive Grid, Helix, AxeFX and Kemper that Impulse Responses for bass are being used and growing in popularity at an accelerating rate. Even the likes of Darkglass are building pedals that load user preset  IR's on. For the uninitiated, guitarists using overdrive or distortion, cabinet IR's help to shape and make driven tones more palatable - and as bassists are using drive (especially in say prog and metal situations) then IR's for classic bass cabinets are required more and more. I think that you only have to look at the likes of Sigma and other companies who specialise in IR creation to see that demand for bass IR's are growing. I actually managed to grab a download the other day that literally has hundreds, maybe more IR's and many are bass orientated. 

That said, all-analogue hardware examples that allow the mixing of direct and cabinet simulated sound and can also offer up the compression and distortion artefacts of a real amplifier are highly regarded too. P.s. Would like to review the Doug Pinnick pedal in GI please  (Do I win a Q/Strip yet?)