Bo Holm-Rasmussen, Heidi-Maria Lehtonen, and Vesa Välimäki

A New Reverberator Based on Variable Sparsity Convolution

Companion page for a paper submitted for the 16th International Conference on Digital Audio Effects (DAFx-13), Maynooth, Ireland, September 2-6, 2013


An efficient algorithm approximating the late part of room reverberation is proposed. The algorithm partitions the impulse response tail into variable-length segments and replaces them with a set of sparse FIR filters and lowpass filters, cascaded with several Schroeder allpass filters. The sparse FIR filter coefficients are selected from a velvet noise sequence, which consists of ones, minus ones, and zeros only. In this application, it is sufficient perceptually to use very sparse velvet noise sequences having only about 0.1 to 0.2% non-zero elements, with increasing sparsity along the impulse response. The algorithm yields a parametric approximation of the late part of the impulse response, which is more than 100 times more efficient computationally than the direct convolution. The computational load of the proposed algorithm is comparable to that of FFT-based partitioned convolution techniques, but with nearly half the memory usage. The main advantage of the new reverberator is the flexible parameterization.

Sound Examples

The reference impulse response (zip-file containing s1_r3_o.wav) measured from the concert hall in Pori, Finland, available from its original webpage, the replicated impulse response, and the abstract reverb effect impulse response.

The sound examples below demonstrates the proposed algorithm in mono. The recordings are borrowed from here and here.

Dry sound Reference reverb Proposed algorithm Abstract reverb
Jazz guitar guitar_dry_sound.wav guitar_reference_reverb.wav guitar_proposed_algorithm.wav guitar_abstract_reverb.wav
Drum fill drum_dry_sound.wav drum_reference_reverb.wav drum_proposed_algorithm.wav drum_abstract_reverb.wav
Updated on Monday June 17, 2013