What Is an IR (Cab Impulse Response) and When Does NAM Need One?
If your amp model sounds like a swarm of bees, you are probably missing an IR. Here is what impulse responses are, why they matter so much, and how to pick one.
Basics NAM Hub team · October 2, 2026 · 5 min read
What an IR is
An impulse response (IR) is a short audio file that captures how a speaker cabinet — together with a microphone in a specific position — colours sound. When you load it, your signal is filtered exactly as if it were played through that cab and recorded with that mic.
IRs are usually small .wav files. Almost every amp simulator, multi-effect and DAW can load them; the NAM plugin has a built-in IR slot as well.
Why a cabinet matters so much
A guitar speaker is not a neutral loudspeaker. It cuts most of the very low and very high frequencies and adds its own peaks and dips. That filtering turns the raw, buzzy output of an amplifier into the familiar guitar tone. Without it, distortion sounds harsh and fizzy.
When NAM needs an IR — and when it doesn't
| Model type | Add an IR? |
|---|---|
| Amp only / DI / direct out / load box | Yes, always |
| Preamp capture | Yes |
| Full rig (amp + cab + mic) | No |
| Pedal capture going into another amp model | Only after the amp model, if that amp is "amp only" |
How to choose an IR
- Cabinet size: 4x12 cabs sound big and tight; 2x12 and 1x12 sound more open and focused, often great for blues and clean tones.
- Speaker: Vintage 30-style speakers are mid-forward and aggressive (rock, metal); Greenback-style are warmer and vintage; Jensen-style and other American-voiced speakers suit clean and crunchy tones.
- Microphone: dynamic mics such as the SM57 type are bright and punchy; ribbon mics are smoother and darker. Many IRs blend two mics.
- Position: closer to the centre of the cone = brighter; towards the edge or off-axis = darker.
Practical tips
- Start with a classic "4x12 V30 + SM57" style IR for rock and a 1x12 or 2x12 IR for cleans.
- Match the sample rate (most often 48 kHz) to avoid quality loss or extra processing.
- Use a high-cut (around 6–8 kHz) and low-cut (around 80–100 Hz) EQ after the IR to tame fizz and boom.
- Compare IRs at the same volume — loudness changes our perception.
- Many good IR packs are free; manufacturers also sell professional ones.
Next: avoid the other classic mistakes in 5 common beginner mistakes, or learn to read file descriptions in this guide.
Keep reading
How to Read a NAM Model Description: Gain, Cab and Mic
What to check in a NAM file listing before you download: capture type, amp settings, cab and mic, input level, model size and ESR.
Beginners5 Common Beginner Mistakes the First Time You Run NAM
Missing IR, two cabinets in a row, wrong input level, effects in the wrong order and audio settings — the five most common NAM beginner mistakes and how to fix them.
CreateGPU vs CPU: What Is Faster for Training Your Own NAM Model?
Do you need a graphics card to train a NAM model? Training on a GPU, CPU, Apple Silicon or free cloud notebooks compared — with practical tips to save time.