*Updated 10/15/2022 to include Linux Studio Plugins.
When I first really got started recording instruments, I began hearing about something called IR’s and had to dig to find out what they were. I was a late bloomer it seems.
IR stands for Impulse Response. Essentially an IR is a recording of a sound (like a guitar) played though a speaker (cabinet) in a environment (ie: studio live room) through a specific microphone. The final recorded file is just a wav or an aif with wav being much more common.
You load up your IR file into an impulse response loader, which is added to a track that contains a DI guitar and an amp sim of some sort, and the IR mimics the sound of the cab/microphone/room that was recorded.
IR’s are a must have if you’re using straight up amp sims on your guitar tracks. Normally amp sims on their own don’t sound super great; they’re very dry and don’t have a ton of “character”. Stick an IR of, for example, a Fender Tweed Champ 58 on the track and you’ll notice a big difference right away.
IRs can also be used for reverb. Similar to the idea of capturing a sound of specific amp/mics/rooms, reverb impulses capture the ambiance of specific places be it a famous concert hall, the space under a bridge, or even a school hallway.
While there are a ton of IR loaders out there, both paid and free, as with everything else, a good percentage of them are for Windows and/or Mac.1
All is not lost and there are Linux options, and they’re damn good.