Directional Feedback Delay Network

Abstract

Artificial reverberation algorithms are used to enhance dry audio signals. Delay-based reverberators can produce a realistic effect at a reasonable computational cost. While the recent popularity of spatial audio algorithms is mainly related to the reproduction of the perceived direction of sound sources, there is also a need to spatialize the reverberant sound field. Usually multichannel reverberation algorithms output a series of decorrelated signals yielding an isotropic energy decay. This means that the reverberation time is uniform in all directions. However, the acoustics of physical spaces can exhibit more complex direction-dependent characteristics. This paper proposes a new method to control the directional distribution of energy over time, within a delay-based reverberator, capable of producing a directional impulse response with anisotropic energy decay. We present a method using multichannel delay lines in conjunction with a direction-dependent transform in the spherical harmonic domain to control the direction-dependent decay of the late reverberation. The new reverberator extends the feedback delay network, retaining its time-frequency domain characteristics. The proposed directional feedback delay network reverberator can produce non-uniform direction-dependent decay time, suitable for anisotropic decay reproduction on a loudspeaker array or in binaural playback through the use of ambisonics.

Perceptual Matching of Room Acoustics for Auditory Augmented Reality in Small Rooms - Literature Review and Theoretical Framework

“…Besides, for example, semantic and visual information can be used to estimate acoustic properties (Kim et al, 2017(Kim et al, , 2020. BRIR synthesis can be realized either by pure simulation, for example, based on ray-tracing (Savioja & Svensson, 2015;Brinkmann et al, 2019), wave-based simulation approaches or delay networks (Alary et al, 2019;Välimäki et al, 2012) or by manipulation of measured impulse responses, like interpolation (Bruschi et al, 2020;Brinkmann et al, 2020), extrapolation (Neidhardt et al, 2018;Sloma et al, 2019;Coleman et al, 2017;Pörschmann et al, 2017) or shaping of the late reverberation tail (Jot & Lee, 2016;Pörschmann & Zebisch, 2012;Arend et al, 2021). Systems that do not rely on a priori knowledge are desired because their use is not limited to rooms or environments for which the predetermined information is available.…”

“…Another approach is the use of feedback-delay networks (FDNs). Based on a direction-dependent target reverberation time, Alary et al (2019) create directional anisotropic reverberation with a directional FDN. Depending on the specific application, the trade-off between spatial accuracy and computational costs has to be considered.…”

Comparing modeled and measurement-based spherical harmonic encoding filters for spherical microphone arrays

“…Lecomte et al [30] showcases similar spatial effects. Finally, Alary et al [31] uses them to modify the directional power response of a feedback delay network operating on Ambisonic signals resulting in non-uniform reverberation time across different directions.…”

Auditory perception stability evaluation comparing binaural and loudspeaker Ambisonic presentations of dynamic virtual concert auralizations

“…Ambisonic is a format that allows for the representation of a 3D-sound field through the use of spherical harmonics (SH) (Nicol, 2010). This format, agnostic to rendering configuration, allows easy spatial manipulations, such as rotation, directional loudness control, and warping (Alary et al, 2019;Zotter and Frank, 2019). Ambisonics provides a decoupling between encoder and decoder.…”