Impulses are like "snapshots" of an amp or cab used to model.
You use an impulse loader VST or program or whatnot and load this 8-second or so .wav files that tell the host how to change the sound to mimick a cab or amp. Much like POD Farm or an Axe FX unit. POD Farm doesn't have good-quality cab impulses though, no anything based on GK gear. Their bass amp system is all flawed.
Here's a video example
‪How To Use Impulses‬‏ - YouTube
As you can see, he goes and pick the JJ Powertube cab, then selects the microphone setting he wants, and it emulates the sound,
You can make your own, but I don't have to equipment nor skill.
They're especially useful for recording in apartments, at night, with families, or getting the same sound consistently and saving a ton of time at live shows.
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