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Computational costs of different FDN and VFDN config- urations.
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Artificial reverberation is an audio effect used to simulate the acoustics of a space while controlling its aesthetics, particularly on sounds recorded in a dry studio environment. Delay-based methods are a family of artificial reverberators using recirculating delay lines to create this effect. The feedback delay network is a popular delay-based r...
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... since the spectral deviation is constant, it is possible to introduce a set of equalization filters at the final outputs to compensate for the coloration. Table 1 shows the number of operations per output sample for the configurations presented in Fig. 7. These numbers are computed for a practical setup using fourth-order attenuation filters consisting of a second-order low-shelf, a second-order high-shelf, and DAFx.6 DAF 2 x 21 in gain for middle frequencies. ...Context 2
... FDN32 structure is used as the reference method to calculate the amount of savings, since it is the target we used for the echo density measure. A comparison between the VFDN16 structures implemented using OVN15 and VN15 highlights the added cost of using decaying VNSs, which shows in the number of multiplications in Table 1. The proposed configuration using OVN15 and VN15 save 35% and 52% of operations, respectively, so they both still use considerably less operations than the reference method FDN32. ...Context 3
... counting additions and multiplications separately may not be relevant on modern hardware, Table 1 follows the typical method of presenting the computational cost and from which also the Multiply and Accumulate (MAC) operations can be derived. Here, we used a dense random orthogonal matrix in the FDN recirculation path. ...Similar publications
Available online with the related articles at: http://urn.fi/URN:ISBN:978-952-64-0472-1
In this dissertation, the reproduction of reverberant sound fields containing directional characteristics is investigated. A complete framework for the objective and subjective analysis of directional reverberation is introduced, along with reverberation method...
Citations
... While most of these optimization methods rely on traditional reverberator methods, recent advancements, such as the use of velvet noise to reproduce RIRs [12] and to improve modal density in lower-order FDNs [13], may prove beneficial. Other improvements in FDN-based reverberators include a method to find the optimal mixing matrix to achieve a colorless prototype [14,15] and a two-stage filter design to improve the accuracy of attenuation filters in the feedback path [16]. ...
This paper seeks to improve the state-of-the-art in delay-network-based analysis-synthesis of measured room impulse responses (RIRs). We propose an informed method incorporating improved energy decay estimation and synthesis with an optimized feedback delay network. The performance of the presented method is compared against an end-to-end deep-learning approach. A formal listening test was conducted where participants assessed the similarity of reverberated material across seven distinct RIRs and three different sound sources. The results reveal that the performance of these methods is influenced by both the excitation sounds and the reverberation conditions. Nonetheless, the proposed method consistently demonstrates higher similarity ratings compared to the end-to-end approach across most conditions. However, achieving an indistinguishable synthesis of measured RIRs remains a persistent challenge, underscoring the complexity of this problem. Overall, this work helps improve the sound quality of analysis-based artificial reverberation.
... An optimization scheme for minimizing the spectral coloration introduced by the velvet-noise decorrelator was proposed in [14]. Velvet noise has been also used in hybrid reverb structures combining it with feedback delay networks (FDN) [15,16]. Short velvet-noise filters are applied either within the feedback matrix [16] or at the inputs and outputs of the FDN [15]. ...
... Velvet noise has been also used in hybrid reverb structures combining it with feedback delay networks (FDN) [15,16]. Short velvet-noise filters are applied either within the feedback matrix [16] or at the inputs and outputs of the FDN [15]. Additionally, velvet-noise has been used in vocoder-based speech generation by serving as excitation signals [17]. ...
Velvet noise is a sparse pseudo-random signal, with applications in late reverberation modeling, decorrelation, speech generation, and extending signals. The temporal roughness of broadband velvet noise has been studied earlier. However, the frequency-dependency of the temporal roughness has little previous research. This paper explores which combinative qualities such as pulse density, filter type, and filter shape contribute to frequency-dependent temporal roughness. An adaptive perceptual test was conducted to find minimal densities of smooth noise at octave bands as well as corresponding lowpass bands. The results showed that the cutoff frequency of a lowpass filter as well as the center frequency of an octave filter is correlated with the perceived minimal density of smooth noise. When the lowpass filter with the lowest cutoff frequency, 125 Hz, was applied, the filtered velvet noise sounded smooth at an average of 725 pulses/s and an average of 401 pulses/s for octave filtered noise at a center frequency of 125 Hz. For the broadband velvet noise, the minimal density of smoothness was found to be at an average of 1554 pulses/s. The results of this paper are applicable in designing velvet-noise-based artificial reverberation with minimal pulse density.
... Low multichannel correlation can also be generated by recombining multiple uncorrelated channels by an orthogonal mixing matrix [16,17]. Correlation can be reduced by additional decorrelation filtering, such as with a white noise sequence [4], subband techniques [18], an allpass filter [19,20], or a velvet-noise sequence [21][22][23]. ...
The feedback delay network (FDN) is a popular filter structure to generate artificial spatial reverberation. A common requirement for multichannel late reverberation is that the output signals are well decorrelated, as too high a correlation can lead to poor reproduction of source image and uncontrolled coloration. This article presents the analysis of multichannel correlation induced by FDNs. It is shown that the correlation depends primarily on the feedforward paths, while the long reverberation tail produced by the recursive path does not contribute to the inter-channel correlation. The impact of the feedback matrix type, size, and delays on the inter-channel correlation is demonstrated. The results show that small FDNs with a few feedback channels tend to have a high inter-channel correlation, and that the use of a filter feedback matrix significantly improves the decorrelation, often leading to the lowest inter-channel correlation among the tested cases. The learnings of this work support the practical design of multichannel artificial reverberators for immersive audio applications.
... The idea of reverberation modelling with VN was continued by applying filtered sparse sequences to approximate segments of the late part of an RIR, at the same time closely following the target decay of each of such fragments [222,223]. Recently, VN signals were inserted in an FDN architecture to enhance the diffuseness of produced sounds [224,225,226]. ...
In this dissertation, the discussion is centered around the sound energy decay in enclosed spaces. The work starts with the methods to predict the reverberation parameters, followed by the room impulse response measurement procedures, and ends with an analysis of techniques to digitally reproduce the sound decay.
The research on the reverberation in physical spaces was initiated when the first formula to calculate room's reverberation time emerged. Since then, finding an accurate and reliable method to predict reverberation has been an important area of acoustic research. This thesis presents a comprehensive comparison of the most commonly used reverberation time formulas, describes their applicability in various scenarios, and discusses their accuracy when compared to results of measurements. The common sources of uncertainty in reverberation time calculations, such as bias introduced by air absorption and error in sound absorption coefficient, are analyzed as well. The thesis shows that decreasing such uncertainties leads to a good prediction accuracy of Sabine and Eyring equations in diverse conditions regarding sound absorption distribution.
The measurement of the sound energy decay plays a crucial part in understanding the propagation of sound in physical spaces. Nowadays, numerous techniques to capture room impulse responses are available, each having its advantages and drawbacks. In this dissertation, the majority of commonly used measurement techniques are listed, whereas the exponential swept-sine is described in more detail. This work elaborates on the external factors that may impair the measurements and introduce error to their results, such as stationary and non-stationary noise, as well as time variance. The dissertation introduces Rule of Two, a method of detecting nonstationary disturbances in sweep measurements. It also shows the importance of using median as
a robust estimator in non-stationary noise detection.
Artificial reverberation is a popular sound effect, used to synthesize sound energy decay for the purpose of audio production. This dissertation offers an insight into artificial reverberation algorithms based on recursive structures. The filter design proposed in this work offers precise control over the decay rate while being efficient enough for real-time implementation. The thesis discusses the role of the delay lines and feedback matrix in achieving high echo density in feedback delay networks. It also shows that four velvet-noise sequences are sufficient to obtain smooth output in interleaved velvet noise reverberator. The thesis shows that the accuracy of reproduction increases the perceptual similarity between measured and synthesised impulse responses.
The insights collected in this dissertation offer insights into the intricacies of reverberation prediction, measurement and synthesis. The results allow for reliable estimation of parameters related to sound energy decay, and offer an improvement in the field of artificial reverberation.
... Several different reverberation algorithms utilizing velvet noise have been proposed in the past [8,9,10,11,12]. Other applications include speech synthesis [13], where modified velvet noise has been used to generate unvoiced speech sounds. ...
This paper proposes dark velvet noise (DVN) as an extension of the original velvet noise with a lowpass spectrum. The lowpass spectrum is achieved by allowing each pulse in the sparse sequence to have a randomized pulse width. The cutoff frequency is controlled by the density of the sequence. The modulated pulse-width can be implemented efficiently utilizing a discrete set of recursive running-sum filters, one for each unique pulse width. DVN may be used in reverberation algorithms. Typical room reverberation has a frequency-dependent decay, where the high frequencies decay faster than the low ones. A similar effect is achieved by lowering the density and increasing the pulse-width of DVN in time, thereby making the DVN suitable for artificial reverberation.
... Recent research extended Schroeder allpass filters and reverberators, e.g., allowing frequency-dependent gains in Schroeder allpass filters [35]; connecting FDNs to room geometry [36]; adding controls of directional distribution of sound to FDNs [37]; imbuing FDNs with the allpass prop- erty [34]; generalizing FDN feedback to a matrix of filters [38], including the case of velvet noise [39,40] feedback matrices in particular [41]; and studying coupled and parallel FDNs [42,43]. This article complements these works, providing new insight on Schroeder allpass filters and FDN architectures with good time-varying properties. ...
... This is equivalent to what we found in (41). Since the filter output's energy is equal to the filter input's energy, we say that it is "energy-preserving." ...
... Parametric reverberation algorithms suitable for this purpose have been extensively studied, including methods for analyzing, simulating or "sculpting" recorded, simulated or calculated reverberation responses [73]- [79]. Many involve a recirculating delay network as illustrated in Fig. 16 -where, referring to the reverberation API properties introduced in Section II-A2 [73], [75], [80], ...
Interactive audio spatialization technology previously developed for video game authoring and rendering has evolved into an essential component of platforms enabling shared immersive virtual experiences for future co-presence, remote collaboration and entertainment applications. New wearable virtual and augmented reality displays employ real-time binaural audio computing engines rendering multiple digital objects and supporting the free navigation of networked participants or their avatars through a juxtaposition of environments, real and virtual, often referred to as the Metaverse. These applications require a parametric audio scene programming interface to facilitate the creation and deployment of shared, dynamic and realistic virtual 3D worlds on mobile computing platforms and remote servers. We propose a practical approach for designing parametric 6-degree-of-freedom object-based interactive audio engines to deliver the perceptually relevant binaural cues necessary for audio/visual and virtual/real congruence in Metaverse experiences. We address the effects of room reverberation, acoustic reflectors, and obstacles in both the virtual and real environments, and discuss how such effects may be driven by combinations of pre-computed and real-time acoustic propagation solvers. We envision an open scene description model distilled to facilitate the development of interoperable applications distributed across multiple platforms, where each audio object represents, to the user, a natural sound source having controllable distance, size, orientation, and acoustic radiation properties.
... Parametric reverberation algorithms suitable for this purpose have been extensively studied, including methods for analyzing, simulating or "sculpting" recorded, simulated or calculated reverberation responses [73]- [79]. Many involve a recirculating delay network as illustrated in Fig. 16 -where, referring to the reverberation API properties introduced in Section II-A2 [73], [75], [80], ...
Interactive audio spatialization technology previously developed for video game authoring and rendering has evolved into an essential component of platforms enabling shared immersive virtual experiences for future co-presence, remote collaboration and entertainment applications. New wearable virtual and augmented reality displays employ real-time binaural audio computing engines rendering multiple digital objects and supporting the free navigation of networked participants or their avatars through a juxtaposition of environments, real and virtual, often referred to as the Metaverse. These applications require a parametric audio scene programming interface to facilitate the creation and deployment of shared, dynamic and realistic virtual 3D worlds on mobile computing platforms and remote servers. We propose a practical approach for designing parametric 6-degree-of-freedom object-based interactive audio engines to deliver the perceptually relevant binaural cues necessary for audio/visual and virtual/real congruence in Metaverse experiences. We address the effects of room reverberation, acoustic reflectors, and obstacles in both the virtual and real environments, and discuss how such effects may be driven by combinations of pre-computed and real-time acoustic propagation solvers. We envision an open scene description model distilled to facilitate the development of interoperable applications distributed across multiple platforms, where each audio object represents, to the user, a natural sound source having controllable distance, size, orientation, and acoustic radiation properties.
... Our recent work shows that the smallest useful order of the FDN is 16 [47], whereas Alary et al. point out that an order as high as 32 may be necessary to achieve sufficient echo and modal densities, depending on the algorithm implementation [48]. Fagerström et al. consider the reverberation produced by an FDN of order 32 as sufficiently dense and the one synthesized with a 16th-order FDN as slightly too sparse [49]. For fairness, we choose here the order 16 as the smallest order for the FDN that is useful for high-quality audio. ...
This paper proposes a novel algorithm for simulating the late part of room reverberation. A well-known fact is that a room impulse response sounds similar to exponentially decaying filtered noise some time after the beginning. The algorithm proposed here employs several velvet-noise sequences in parallel and combines them so that their non-zero samples never occur at the same time. Each velvet-noise sequence is driven by the same input signal but is filtered with its own feedback filter which has the same delay-line length as the velvet-noise sequence. The resulting response is sparse and consists of filtered noise that decays approximately exponentially with a given frequency-dependent reverberation time profile. We show via a formal listening test that four interleaved branches are sufficient to produce a smooth high-quality response. The outputs of the branches connected in different combinations produce decorrelated output signals for multichannel reproduction. The proposed method is compared with a state-of-the-art delay-based reverberation method and its advantages are pointed out. The computational load of the method is 60% smaller than that of a comparable existing method, the feedback delay network. The proposed method is well suited to the synthesis of diffuse late reverberation in audio and music production.
