How to capture an impulse response (IR) from an amp (with free plugins) Part 1/2

Hello and welcome to this week's article!

Today we are talking about an extremely interesting topic: how to capture an Impulse Response.

Impulse responses consist, said in very simple terms, in playing a sound that covers all audible frequences from a source and capturing it with a microphone, then we subtract the original sound from the captured wave and what remains is the interaction between the source, the ambient in which the sound is played, and the microphone that captured it.
This resulting file can be applied in form of Reverb to any track we have, so that a vocal track can sound as it's recorded in a church, or in a room without resonances, or in the shower booth and so on.

Impulse responses are particularly interesting in the world of home recording for one purpose: amp simulators;
why? Because amp modeling is out there by 20 to 30 years (according to whether we are considering also the analog simulation), and still, even if the circuitry of the amp today is emulated to an impressive degree of realism, there is a technological bottleneck regarding cab simulation, somehow it never seems to sound close enough to the real thing and it's the main reason why people still in 2019 keeps making records using the same techniques of 50 years ago.

Impulse responses are a workaround to this technological bottleneck: they substitute completely the other types of cabinet simulations, and just replace them with a Reverb that recreates the sound captured from the guitar cab with a microphone; the result is so much more realistic that this technique has basically substituted completely all the other ways of simulating a cabinet, and are (in a slightly more elaborated way) the core of high end digital guitar amps such as the Kemper.

Internet is full of great impulses that can be downloaded for free (such as the Guitarhack or the Catharsis ones) or paid (like the Ownhammer ones), but if we have the right tools we can do them on our own, so that we just need to capture with our microphone and cab all the positions once, and then we can have fun at home without having to set up the recording gear every time.


What do we need to capture an IR?

A good guitar amp (possibly with a tube power amp) with effects loop and a good cabinet

A microphone (possibly an industry standard such a Shure SM57)

A good audio interface connected to a computer with a Daw

A software that creates impulses, such as Voxengo Deconvolver, that can be used for free with some limitation, but that is perfectly usable to create IRs.


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