Convolution reverb is a technique that applies the acoustics of a real or virtual space to an audio signal by convolving it with an impulse response recorded in that space.
Convolution reverb uses the mathematical operation of convolution to apply the characteristics of an environment (captured as an impulse response, or IR) to a dry audio signal. This allows you to simulate how a sound would behave in real acoustic spaces.:
Strengths:
- Convolution reverb can capture the acoustics of existing places.
- High quality results.
Drawbacks:
- Not dynamic.
- Not parametric.
- Computationally complex (for long IRs).
Impulse Responses¶
The principle of an impulse response (IR) in acoustics (and for IR reverbs) is the same as in DSP in general: A system is excited with an impulse and its response is recorded.
There are different methods to create that impulse:
- Handclap
- Balloon Pop
- Starter Pistol
Another way is to use a sine sweep and transform the response.
A Stereo IR¶
IRs can be recorded and applied in any format. Mono, stereo, binaural, Ambisonics, ... Since stereo has been the dominant format for a long time, there are countless stereo IRs available. This example was recorded in a small church (MD, Germany) with a field recorder, using a hand-clap as excitation:
Applying Convolution¶
We can convolve the dry audio with the impulse response to simulate reverberation. Since we have a stereo IR, we perform two convolutions to use the spatial information and create a stereo signal from our mono input.
Visualizing the Signals¶
Here we visualize the waveforms for the dry signal, the impulse response, and the resulting reverberated signal.
Listen to the Audio¶
Playback of the dry, IR, and wet signals.
Dry Audio:
Wet Audio (Reverberated):
Exercise¶
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1: Download a solo: https://ringbuffer.org/download/audio/solo_instruments/
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2: Download one of these IRs: https://ringbuffer.org/download/audio/ir/
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3: Apply convolution to create a reverberant version of the solo.