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A recent publication introduced the Directional Feedback Delay Network, a parametric artificial reverberation algorithm capable of producing direction-dependent energy decay. This method extends the capabilities of Feedback Delay Networks by using multichannel delay-line groups and a spatial transform to produce direction-dependent reverberation in the Ambisonics domain. In this paper, we present a modified formulation of the Directional Feedback Delay Network method that allows both frequency-and direction-dependent reverberation. Multichannel delay-line groups are used to manipulate signals incident on a spherical grid through independent recursive signal paths, while an early reflection module gives a physically-motivated spatial distribution of input signals in the system. The overall number of delay lines is reduced from the previous formulation, and the design allows flexibility to favor a lower computational cost over accuracy. acceptedVersion

Feedback delay networks (FDNs) belong to a general class of recursive filters which are widely used in sound synthesis and physical modeling applications. We present a numerical technique to compute the modal decomposition of the FDN transfer function. The proposed pole finding algorithm is based on the Ehrlich-Aberth iteration for matrix polynomials and has improved computational performance of up to three orders of magnitude compared to a scalar polynomial root finder. The computational performance is further improved by bounds on the pole location and an approximate iteration step. We demonstrate how explicit knowledge of the FDN's modal behavior facilitates analysis and improvements for artificial reverberation. The statistical distribution of mode frequency and residue magnitudes demonstrate that relatively few modes contribute a large portion of impulse response energy.

In this design study, we introduce a novel class of digital audio effects that extend the recently introduced modal processor approach to artificial reverberation and effects processing. These pitch and distortion processing effects mimic the design and sonics of a classic additive-synthesis-based electromechanical musical instrument, the Hammond tonewheel organ. As a reverb effect, the modal processor simulates a room response as the sum of resonant filter responses. This architecture provides precise, interactive control over the frequency, damping, and complex amplitude of each mode. Into this framework, we introduce two types of processing effects: pitch effects inspired by the Hammond organ’s equal tempered “tonewheels”, “drawbar” tone controls, vibrato/chorus circuit, and distortion effects inspired by the pseudo-sinusoidal shape of its tonewheels and electromagnetic pickup distortion. The result is an effects processor that imprints the Hammond organ’s sonics onto any audio input.

cote interne IRCAM: Jot99a; None / None; National audience; This paper overviews the principles and methods for synthesizing complex three-dimensional sound scenes by processing multiple individual source signals. Signal processing techniques for directional sound encoding and rendering over loudspeakers or headphones are reviewed, as well as algorithms and interface models for synthesizing and dynamically controlling room reverberation and distance effects. A real-time modular spatial sound processing software system, called Spat, is presented. It allows reproducing and controlling the localization of sound sources in three dimensions and the reverberation of sounds in an existing or virtual space. A particular aim of the Spatialisateur project is to provide direct and computationally efficient control over perceptually relevant parameters describing the interaction of each sound source with the virtual space, irrespective of the chosen reproduction format over loudspeakers or headphones. The advantages of this approach are illustrated in practical contexts, including professional audio, computer music, multimodal immersive simulation systems, and architectural acoustics.

It is shown that half of the points on the diamond grid are redundant for sampling and reconstructing a bandlimited 3-D signal. This redundancy is then exploited to show that the tetrahedral digital waveguide mesh requires four times more computational density and twice the memory storage for the same approximation as a finite difference scheme on the face-centered cubic lattice.