IR Cabinets (Cabinet Simulation)

A large part of what you hear from a miked amp doesn't come from the amplifier at all but from the speaker cabinet, microphone and room. Modelers reproduce that via impulse responses (IRs) — a building block that strongly co-determines the quality of digital sounds.

What an IR is — An impulse response is a kind of acoustic "fingerprint": the recording of how a particular cab with a particular microphone in a particular position sounds. The modeler convolves the dry amp signal with this IR and thus produces the sound of exactly that cab-microphone combination — very realistic, because it maps a real measurement.

Why it matters — The same simulated amp sounds distinctly different through different IRs — just like a real head through different cabs (see the "Speakers" topic). The IR is thus one of the most effective controls for a modeler sound's end result. Many "my modeler sounds digital" complaints resolve with a better IR.

In practice — Modelers come with IRs; additionally, third-party IRs can be loaded. Experimenting with IRs (different cabs, microphones, positions) is often more rewarding than constantly switching the amp model.

For the direct path to the mixing desk or the DAW, IR cabinet simulation is the key — it replaces cab, microphone and miking with a measurement. No approach is "more correct"; the fitting IR is the one that leads to the desired sound.