The Impulse Response
Clap in a cathedral. That echo is the room's fingerprint, called an impulse response. Stamp it onto any dry sound and suddenly you're in the cathedral.
What Is an Impulse Response?
Every space responds to sound differently. A cathedral rings for seconds. A tiled bathroom is bright and tight. A metal plate shimmers.
If you fire an infinitely short click (an impulse) into any of these spaces, the reverberations you record back are that space's impulse response (IR). It captures the size, shape, and materials of the environment in a single waveform.
Convolution Reverb
A convolution reverb takes a recorded IR and mathematically "stamps" it onto your dry signal. Every sample gets multiplied by the entire IR and summed together. The result sounds like your signal was actually played in that space.
This is different from the algorithmic reverb in Part 22, which simulates reflections with delay networks. Convolution reproduces the exact acoustic character of a real space. It also works on plates, springs, speakers, and EQ curves.
The IR Shapes Sound
Look at the IR waveform display below. A cathedral IR is long with sparse early reflections that build into a dense tail. A small room is short and punchy. A plate is bright and shimmering. A spring has that metallic "boing" from its comb-filtered resonances.
The dry/wet mix controls how much reverb you hear. Hit A/B to flip between dry and your current mix.
Try it: switch between IRs and hear how each one transforms the same source. Use A/B to compare. Try the "Click" source to hear the raw impulse response.
Why It Matters
With a library of impulse responses, you can put any sound in any space. Concert hall, cardboard box, vintage spring tank. The same technique works for modelling guitar cabinets and vintage EQs too.