Karolina Prawda, Sebastian J. Schlecht and Vesa Välimäki
Companion page for a paper submitted to the 25th International Conference on Digital Audio Effects (DAFx 2022)
The published paper can be found here.
The cross-correlation of multichannel reverberation generated using interleaved velvet noise is studied. The interleaved velvet-noise reverberator was proposed recently for synthesizing the late reverb of an acoustic space. In addition to providing a computationally efficient structure and a perceptually smooth response, the interleaving method allows combining its independent branch outputs in different permutations, which are all equally smooth and flutter-free. For instance, a four-branch output can be combined in 4! or 24 ways. Additionally, each branch output set is mixed orthogonally, which increases the number of permutations from M! to M^2!, since sign inversions are taken along. Using specific matrices for this operation, which change the sign of velvet-noise sequences, decreases the correlation of some of the combinations. This paper shows that many selections of permutations offer a set of well decorrelated output channels, which produce a diffuse and colorless sound field, which is validated with spatial variation. The results of this work can be applied in the design of computationally efficient multichannel reverberators.
To illustrate the spatial variance and multichannel correlation, we provide three binaural renderings. The multichannel reverberation impulse response is played through 16 or 24 virtual loudspeaker positions. The binaural rendering applies the appropriate HRTFs, distance gain, and delay for the loudspeaker position. A moving receiver position demonstrates the spatial variance with about +-2 m within 2-3 seconds. The movement exaggerates the effect of a person's head moving in an anechoic chamber with multichannel playback. The same signal from all loudspeakers results in the superposition of multiple comb filters is perceived as 'warbling.' Well-decorrelated sound by IVN permutation significantly reduced this effect. Informal listening has confirmed that a similar result can be achieved with physical playback in an anechoic room.
16 loudspeakers, the same signal
24 loudspeakers, basic permutations
16 loudspeakers, with orthogonal mixing