On Lossless Feedback Delay Networks

Schlecht, Sebastian J.; Habets, Emanuël A. P.

doi:10.1109/tsp.2016.2637323

Cited by 19 publications

(24 citation statements)

References 49 publications

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“…In this way, the application of both S W GW and S recombines the N (N − 1)(N − 1) channels present in the feedback loop back into the N (N − 1) inter-node wave variables required for reinsertion and further propagation through the system. Since the WGW makes use of essentially the same scattering operation as the SDN, it is similarly stable [10] regardless of the length of the delay lines connecting the nodes. As a result the addition of losses at the nodes will always result in a stable network.…”

Section: Feedback Loopmentioning

confidence: 99%

“…A RTIFICIAL reverberation research has, until recently, striven mainly for the realistic imitation of rooms, concert halls, and other indoor acoustic spaces [1], [2]. For this purpose, there are several specialized modeling techniques, such as the ray-tracing [3], image-source [4], [5], digital waveguide [6], [7], feedback delay networks (FDNs) [8]- [10], and finitedifference time-domain (FDTD) [11]- [14] methods. However, there has been relatively little research looking at modeling of sparsely reflecting outdoor acoustic scenes, although environmental sound is of significant importance, particularly because of the propagation of noise pollution over distances and its impact on human health and well-being [15].…”

Section: Introductionmentioning

confidence: 99%

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Modeling Sparsely Reflecting Outdoor Acoustic Scenes Using the Waveguide Web

Stevens

Murphy

Savioja

et al. 2017

IEEE/ACM Trans. Audio Speech Lang. Process.

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Computer games and virtual reality require digital reverberation algorithms, which can simulate a broad range of acoustic spaces, including locations in the open air. Additionally, the detailed simulation of environmental sound is an area of significant interest due to the propagation of noise pollution over distances and its related impact on well-being, particularly in urban spaces. This paper introduces the waveguide web digital reverberator design for modeling the acoustics of sparsely reflecting outdoor environments; a design that is, in part, an extension of the scattering delay network reverberator. The design of the algorithm is based on a set of digital waveguides connected by scattering junctions at nodes that represent the reflection points of the environment under study. The structure of the proposed reverberator allows for accurate reproduction of reflections between discrete reflection points. Approximation errors are caused when the assumption of point-like nodes does not hold true. Three example cases are presented comparing waveguide web simulated impulse responses for a traditional shoebox room, a forest scenario, and an urban courtyard, with impulse responses created using other simulation methods or from real-world measurements. The waveguide web algorithm can better enable the acoustic simulation of outdoor spaces and so contribute toward sound design for virtual reality applications, gaming, and auralization, with a particular focus on acoustic design for the urban environment.

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Section: Feedback Loopmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Modeling Sparsely Reflecting Outdoor Acoustic Scenes Using the Waveguide Web

Stevens

Murphy

Savioja

et al. 2017

IEEE/ACM Trans. Audio Speech Lang. Process.

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show abstract

“…1. FDNs have well-established system properties such as losslessness and stability [5,6], decay control [7,8], impulse response density [9,10], and, modal distribution [11]. SISO allpass FDNs can be composed from simple allpass filters in series [2,12] or by nesting [13].…”

Section: Introductionmentioning

confidence: 99%

“…They result in homogeneous decay of the impulse response, i.e., all system eigenvalues have the same magnitude [7]. The main contributions of this work are ‚ Improved sufficient condition for an FDN to be stable (Theorem 2) in Section III ‚ Sufficient and necessary conditions for SISO and MIMO FDNs to be uniallpass (Theorems 3 and 4 in Section III) ‚ Characterization of admissible feedback matrices in uniallpass FDN (Section IV-B) 1 The term uniallpass is introduced here with similar motivation as unilossless feedback matrices in [6] which yields lossless FDNs regardless of delay lengths.…”

Section: Introductionmentioning

confidence: 99%

Allpass Feedback Delay Networks

Schlecht

2021

IEEE Trans. Signal Process.

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In the 1960s, Schroeder and Logan introduced delay line-based allpass filters, which are still popular due to their computational efficiency and versatile applicability in artificial reverberation, decorrelation, and dispersive system design. In this work, we extend the theory of allpass systems to any arbitrary connection of delay lines, namely feedback delay networks (FDNs). We present a characterization of uniallpass FDNs, i.e., FDNs, which are allpass for an arbitrary choice of delays. Further, we develop a solution to the completion problem, i.e., given an FDN feedback matrix to determine the remaining gain parameters such that the FDN is allpass. Particularly useful for the completion problem are feedback matrices, which yield a homogeneous decay of all system modes. Finally, we apply the uniallpass characterization to previous FDN designs, namely, Schroeder's series allpass and Gardner's nested allpass for singleinput, single-output systems, and, Poletti's unitary reverberator for multi-input, multi-output systems and demonstrate the significant extension of the design space.

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“…They studied the use of absorptive filters in these systems to maximize the mode density of the response while controlling the decay rate of different frequencies and ensuring consistency within frequency bands. The central lossless property of FDNs has been extensively studied by Rocchesso and Smith [9] and by Schlecht and Habets [10].…”

Section: Introductionmentioning

confidence: 99%

Directional Feedback Delay Network

Alary¹,

Politis²,

Schlecht³

et al. 2019

J. Audio Eng. Soc.

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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.

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On Lossless Feedback Delay Networks

Cited by 19 publications

References 49 publications

Modeling Sparsely Reflecting Outdoor Acoustic Scenes Using the Waveguide Web

Modeling Sparsely Reflecting Outdoor Acoustic Scenes Using the Waveguide Web

Allpass Feedback Delay Networks

Directional Feedback Delay Network

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