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How to apply Convolution Reverb

Mono version

Input/Output data: See how to pass data to KFR

univector<float> audio;
univector<float> impulse_response;
Code
convolve_filter<float> reverb(impulse_response);
reverb.apply(audio);

Note

convolve_filter uses Filter API and preserves its internal state between calls to apply. Audio can be processed in chunks. Use reset function to reset its internal state.

convolve_filter has zero latency.

Internally, FFT is used for performing convolution

True stereo version

Formula

\[ \begin{aligned} out_{L} &= in_{L} * ir_{LL} + in_{R} * ir_{RL}\\ out_{R} &= in_{L} * ir_{LR} + in_{R} * ir_{RR} \end{aligned} \]

where \(*\) is convolution operator.

Input/Output data:

univector<float, 2> stereo_audio;
univector<float, 4> impulse_response;
// impulse_response[0] is left to left
// impulse_response[1] is right to left
// impulse_response[2] is left to right
// impulse_response[3] is right to right
Code
// Prepare filters
convolve_filter<float> reverb_LL(impulse_response[0]);
convolve_filter<float> reverb_LR(impulse_response[1]);
convolve_filter<float> reverb_RL(impulse_response[2]);
convolve_filter<float> reverb_RR(impulse_response[3]);

// Allocate temp data
univector<float> tmp1(stereo_audio[0].size());
univector<float> tmp2(stereo_audio[0].size());
univector<float> tmp3(stereo_audio[0].size());
univector<float> tmp4(stereo_audio[0].size());

// Apply convolution
reverb_LL.apply(tmp1, audio[0]);
reverb_RL.apply(tmp2, audio[1]);
reverb_LR.apply(tmp3, audio[0]);
reverb_RR.apply(tmp4, audio[1]);

// final downmix
audio[0] = tmp1 + tmp2;
audio[1] = tmp3 + tmp4;