What is an impulse response in guitar terms?
An impulse response (or IR) is a sonic measurement of the sound of a speaker, room or microphone in relation to a sound source. In guitar terms, this is usually your amp.
After your guitar itself and the dialled-in tone of your amp, there’s a lot more that can affect your sound. The speaker type, the space you’re in, the microphone you’re using, the microphone’s preamp or position – the list goes on.
The idea of an impulse response is to capture all of that information in one go, so you can instantly recall that setting. This means that wherever you are, you can retain your preferred tone, right down to the detail of your favourite mic placement and room sound. On stage, in the studio, jamming with friends – sorted.
Impulse responses – the scientific bit
It’s worth mentioning at this point that the term ‘impulse response’ is not exclusively used to refer to guitar amps and music production. The scientific explanation is, broadly-speaking, the measurement of an output reacting to a brief input signal (the impulse).
This could be an electronic current, an economic calculation, or a sound – that’s what we’re working with.
How do you use an impulse response?
Impulse responses are usually saved as generic .wav files. Many companies, producers and artists release their own impulse responses that allow you to accurately replicate their sounds. Alternatively, you can create your own – more on this later.
Once you’ve got your chosen IR file, you can load it into compatible hardware or software to reproduce your desired tone. Because impulse responses are becoming more and more commonly used, many manufacturers offer easy built-in ways to utilise them.
Can you use an impulse response with a modelling amp?
Modelling amps are perfect examples of a common IR application. Most of the popular modelling amp varieties have built-in ways of loading in your own impulse response files – whether they’re your own or ones you’ve purchased/downloaded.
Here are some examples IR-compatible modelling amps:
- Line 6 Helix – using Line 6’s free software, you can simply connect your Helix to a computer and import your IR files into the ‘Impulses’ tab.
- Kemper Profiler – use Kemper’s Cab Maker software to convert your IR .wav files into compatible .kipr files. Drop your .kipr files on a USB stick or similar device, then connect it to your Kemper. You can then import using the ‘external storage’ feature.
- Axe-FX – with the Axe-FX III, you can simply drag and drop .wav IR files into the Axe Edit software. To make your files compatible with the Cab Manage feature, you need to download Fractal’s free Cab-Lab software to convert the files.
- Amplifire – simply connect your Amplifire unit and drag and drop your generic .wav IR files – you can then select these in the ‘Cabinet’ section of the Amplifire.
- Headrush – put your Headrush pedalboard into ‘USB Transfer’ mode via global settings and plug in its USB cable. At this point, it’ll show up as a series of folders on your computer; drag and drop your .wav IR files into the ‘Impulse Responses’ folder.
(above: many manufacturers offer easy ways of implementing your own impulse responses, including Headrush)
Can you use an impulse response in a DAW?
The short answer is yes. As with the hardware described above, many DAWs have built-in IR solutions. While some plugins specifically let you use impulse responses (Amplitube, Positive Grid BIAS), they’re more commonly found in convolution reverb effects.
What is convolution reverb?
To put it simply, convolution reverb refers to the simulation of a reverb, echo or the sonic quality of a space using impulse responses. As described earlier, a short sound is played, with the response then being measured and recorded, then recreated using algorithms. Popular convolution reverb plugins include Logic Pro X Space Designer, Waves IR1 and Space by Avid.
What’s the different between an impulse response and a cab sim?
A cab simulator does exactly what the name suggests. It emulates the sound of a guitar cabinet to give your sound an organic ‘realistic’ edge. This is great for both recording and live performance, as it saves you needing to set up a cab with a mic.