What is an Impulse Response (IR)?

An impulse response (IR) is a digital snapshot of how a physical system—like a guitar cabinet, room, or microphone setup—responds to sound. When you load an IR into a compatible device, it applies that acoustic fingerprint to your guitar signal, making it sound as if it's playing through that exact cabinet, in that exact room, with that exact mic placement.

Think of it like a photograph, but for sound. A cabinet IR captures the frequency response, resonance, and character of a real speaker cabinet so you can reproduce it digitally.

How Do Impulse Responses Work?

The technical process is called convolution. Here's the simplified version:

1. A test signal (an "impulse"—a very short burst of sound) is played through a real cabinet, room, or other system
2. The result is recorded with a microphone, capturing how the system shapes the sound
3. This recording becomes the IR file—a small audio file (typically .wav format)
4. When your guitar signal passes through an IR loader, the convolution engine applies the IR to your signal in real-time

The result: your direct guitar signal sounds like it's coming out of a real cabinet, complete with speaker breakup characteristics, frequency response curves, and room ambience.

What is an IR Loader?

An IR loader is any device or plugin that can load and apply impulse response files to your audio signal. IR loaders come in several forms:

• Hardware pedals: Standalone IR loader pedals that sit on your pedalboard
• Multi-effects units: Many modern multi-effects pedals include built-in IR loading capability
• Software plugins: VST/AU plugins for your DAW (recording software)
• Smart amps: Devices like the upcoming Nimbus™ by Chaos Audio include IR loading as a built-in feature

IR Loaders on Chaos Audio Devices

The upcoming Nimbus™ smart amp from Chaos Audio supports loading custom IR files directly onto the device. You can store up to 10 IRs and choose between 256, 512, or 1024 sample lengths for the perfect balance of accuracy and CPU efficiency.

Combined with AIDA-X and NAM neural amp models, Nimbus gives you a complete amp-and-cab solution without needing separate hardware.

Why Guitarists Use IRs

Silent Stage / Direct Recording

Running direct into a PA or audio interface without a real cabinet? IRs make your direct signal sound like it's coming through a miked-up cab. Essential for:

• Recording at home without disturbing neighbors
• Going direct to front-of-house at gigs
• Using in-ear monitors on stage

Tone Matching

Want the sound of a specific cabinet, room, or mic setup? There are IR libraries capturing everything from vintage Marshall 4x12s to modern Friedman cabinets, boutique 1x12 combos, and even famous recording studio rooms.

Consistency

Unlike real cabinets (which sound different depending on the room, mic position, and volume), IRs give you the exact same tone every time. Your bedroom practice tone matches your live tone matches your recording tone.

Types of Impulse Responses

Cabinet IRs

The most common type. These capture the frequency response and character of a guitar or bass cabinet with a specific speaker, recorded with a specific microphone at a specific position. This is what most guitarists mean when they say "IR."

Room IRs

Capture the reverb and ambience of a physical space—a concert hall, recording studio, church, or even a tiled bathroom. Apply a room IR to add natural-sounding space to your tone.

Microphone IRs

Some IRs specifically capture the characteristics of microphone models, letting you apply the color of a Shure SM57, Royer R-121, or other classic mic to your signal.

IR File Formats and Sample Lengths

IRs are typically stored as .wav files at sample rates of 44.1kHz or 48kHz. The key variable is sample length:

• 256 samples: Lowest CPU usage, captures the essential frequency response. Great for live use.
• 512 samples: Good balance of accuracy and performance. Most popular for guitar use.
• 1024 samples: Higher accuracy, captures more of the cab's character including low-end resonance. Uses more CPU.
• 2048+ samples: Studio-quality captures with room ambience. Typically used in DAW plugins.

Where to Find IRs

There's a thriving ecosystem of IR creators:

• Free IRs: Many amp modeler communities share free cabinet IRs
• Commercial IR packs: Companies like Ownhammer, York Audio, Celestion, and 3 Sigma Audio sell premium IR collections
• Capture your own: With the right tools, you can create IRs of your own cabinets

Getting Started with IRs

Ready to explore impulse responses? Here's how to get started:

1. Get an IR-compatible device – A multi-effects pedal with IR loading, a dedicated IR loader pedal, or software plugins
2. Download some IRs – Start with free packs to learn what you like
3. Load and experiment – Try different cabinets, mics, and positions to find your sound
4. Pair with amp modeling – IRs sound best when paired with a good amp model or preamp

The Stratus® multi-effects pedal and the upcoming Nimbus™ smart amp from Chaos Audio both support IRs as part of their open plugin platform. Learn more at chaosaudio.com →