Convolution reverb is one of the most powerful tools in audio and one of the most passively used. You load an impulse response — somebody’s recording of a cathedral, a plate, a spring — and you get that space. The creative act is picking from a list.
Convolution Playground, by Ziv Eliraz of the loopop channel, is built around the other half: designing the impulse response.
What it does
A browser-based application that turns audio files into effects by letting you build impulse responses. Ten ways to design one, per the description: reverse blooms, drawn echoes, chord bodies, filter sweeps, vowels, spectral delays, reverbs, and rain.
You drag in your own audio files or process live instrument input, then visualise the result as a waveform, a frequency response, or a waterfall display.
Free for the full set of sound-design controls and listening. Exporting an IR as a WAV requires a WaveShaper membership on Patreon.
What convolution actually is, and why designing the IR is the interesting part
Convolution takes two signals and produces a third in which every sample of one is multiplied by the entire other and summed. The practical meaning: if you convolve a dry recording with an impulse response, you get the dry recording as it would have sounded inside whatever the IR describes.
The IR is just a recording of what a system does to a single instantaneous click. Fire a starter pistol in a cathedral, record the result, and you have the cathedral’s IR. It encodes the early reflections, the reverb tail, the frequency-dependent absorption — everything.
Here is the thing people under-exploit: nothing requires the IR to be a room.
An IR is a filter, and convolution with an arbitrary signal is an arbitrary filter. So:
- A chord as an IR makes everything you play through it resonate at those pitches — the “chord bodies” in the list. This is how you get a reverb that is harmonically tuned to your track.
- A reversed decay produces a swell into the sound rather than away from it — “reverse blooms”. The effect every trailer uses, built from first principles.
- A vowel formant makes the input speak. Convolving with a recorded “ah” imposes that formant structure on anything.
- A sequence of discrete clicks is a multi-tap delay with an arbitrary rhythm — “drawn echoes”.
- Rain, or any dense stochastic texture, produces a granular smear that no algorithmic reverb will give you.
- A sine sweep is a frequency-dependent time smear.
Everything in that list is a legitimate filter and none of them are rooms. The tool’s contribution is a direct interface for building them, which is the part that has always been missing. You could always make these IRs — in an editor, by hand, by rendering and exporting WAVs and loading them into a convolution plugin and listening and going back. The iteration loop was so slow that almost nobody explored the space.
The three visualisations are not decoration
Waveform, frequency response, and waterfall is exactly the right set, and each answers a different question about an IR:
Waveform tells you the time structure — where the early reflections are, how long the tail is, whether it builds or decays. This is what determines whether the result reads as a space, a delay or a swell.
Frequency response tells you the tonal colour — the IR’s own EQ curve, which gets imposed on everything through it. A bright IR makes everything bright. This is the one people miss, and it is why an unexpected IR can wreck a mix.
Waterfall (a spectrogram over time) tells you how the frequency content changes as it decays, which is where realism lives in a real room and where the interesting artifice lives in a designed one. An IR whose high frequencies die first sounds like a room with soft furnishings; one where they persist sounds metallic and wrong in a way that may be exactly what you want.
Reading those three together is the actual skill, and having them live next to the controls is what makes the tool a learning instrument rather than a toy.
Browser-based, again
This is the third browser-based audio tool we have covered in a week — after Ian Dixon’s Web MIDI synth editors and the Web Serial work — and the pattern is worth naming.
Web Audio is genuinely good now. ConvolverNode has been in the standard since the beginning and is hardware-accelerated; AudioWorklet allows custom DSP on a dedicated audio thread; getUserMedia provides live input. A convolution playground is almost an ideal fit: the heavy operation is one node the browser already implements well, and everything else is UI.
What you get is no install, no platform, no version rot, and a URL you can hand to someone. What you give up is tight integration with a DAW, and sample-accurate sync.
Which maps precisely onto the business model here: exploration is free in the browser, and getting the artifact out costs a Patreon membership. That is an honest split. The expensive part for the developer is not the WAV encoder; it is the hundred hours of DSP and interface work, and gating the export is a reasonable way to fund it while leaving the educational use genuinely free.
How to actually use it
Make IRs from things in your project. Convolve a vocal through a chord from the same song’s harmony. Use a drum hit as the IR for a bass line. Material from inside the track produces results that sit in it.
Short IRs are filters, long IRs are spaces. Under ~50ms and you are shaping timbre; over ~200ms and you are placing the sound somewhere. The middle is where comb filtering and odd resonances live, and that is the most productive region to explore.
Watch the frequency response before you commit. A great-sounding IR with a 6dB bump at 300Hz will muddy everything you put through it, and you will spend an hour EQ-ing a problem you introduced.