Download FDNTB: The Feedback Delay Network Toolbox
Feedback delay networks (FDNs) are recursive filters, which are widely used for artificial reverberation and decorrelation. While there exists a vast literature on a wide variety of reverb topologies, this work aims to provide a unifying framework to design and analyze delay-based reverberators. To this end, we present the Feedback Delay Network Toolbox (FDNTB), a collection of the MATLAB functions and example scripts. The FDNTB includes various representations of FDNs and corresponding translation functions. Further, it provides a selection of special feedback matrices, topologies, and attenuation filters. In particular, more advanced algorithms such as modal decomposition, time-varying matrices, and filter feedback matrices are readily accessible. Furthermore, our toolbox contains several additional FDN designs. Providing MATLAB code under a GNU-GPL 3.0 license and including illustrative examples, we aim to foster research and education in the field of audio processing.
Download A Virtual Instrument for Ifft-Based Additive Synthesis in the Ambisonics Domain
Spatial additive synthesis can be efficiently implemented by applying the inverse Fourier transform to create the individual channels of Ambisonics signals. In the presented work, this approach has been implemented as an audio plugin, allowing the generation and control of basic waveforms and their spatial attributes in a typical DAW-based music production context. Triggered envelopes and low frequency oscillators can be mapped to the spectral shape, source position and source width of the resulting sounds. A technical evaluation shows the computational advantages of the proposed method for additive sounds with high numbers of partials and different Ambisonics orders. The results of a user study indicate the potential of the developed plugin for manipulating the perceived position, source width and timbre coloration.
Download Improving Elevation Perception with a Tool for Image-guided Head-related Transfer Function Selection
This paper proposes an image-guided HRTF selection procedure that exploits the relation between features of the pinna shape and HRTF notches. Using a 2D image of a subject’s pinna, the procedure selects from a database the HRTF set that best fits the anthropometry of that subject. The proposed procedure is designed to be quickly applied and easy to use for a user without previous knowledge on binaural audio technologies. The entire process is evaluated by means of an auditory model for sound localization in the mid-sagittal plane available from previous literature. Using virtual subjects from a HRTF database, a virtual experiment is implemented to assess the vertical localization performance of the database subjects when they are provided with HRTF sets selected by the proposed procedure. Results report a statistically significant improvement in predictions of localization performance for selected HRTFs compared to KEMAR HRTF which is a commercial standard in many binaural audio solutions; moreover, the proposed analysis provides useful indications to refine the perceptually-motivated metrics that guides the selection.
Download Exponential Weighting Method for Sample-by-Sample Update of Warped AR-Model
Auto-regressive (AR) modeling is a powerful tool having many ap­ plications in audio signal processing. The modeling procedure can be focused to low or high frequency range using frequency warp­ ing. Conventionally the AR-modeling procedure is accomplished with frame-by-frame processing which introduces latency. As with any frame-by-frame algorithm full frame has to be available for the algorithm before any output can be produced. This latency makes AR-modeling more or less unusable in real-time sound effects es­ pecially when long frame lengths are required. In this paper we introduce an exponential weighting (EW) method for sample-bysample update of the warped AR-model. This method reduces the latency down to the order of the AR-model.
Download The Sounds of the Avian Syrinx - are they Really Flute-Like?
This research presents a model of the avian vocal tract, implemented using classical waveguide synthesis and numerical methods. The vocal organ of the songbird, the syrinx, has a unique topography of acoustic tubes (a trachea with a bifurcation at its base) making it a rather unique subject for waveguide synthesis. In the upper region of the two bifid bronchi lies a nonlinear vibrating membrane – the primary resonator in sound production. Unlike most reed musical instruments, the more significant displacement of the membrane is perpendicular to the directions of airflow, due to the Bernoulli effect. The model of the membrane displacement, and the resulting pressure through the constriction created by the membrane motion, is therefore derived beginning with the Bernoulli equation.
Download Fixed-rate Modeling of Audio Lumped Systems: A Comparison Between Trapezoidal and Implicit Midpoint Methods
This paper presents a comparison framework to study the relative benefits of the typical trapezoidal method with the lesser-used implicit midpoint method for the simulation of audio lumped systems at a fixed rate. We provide preliminary tools for understanding the behavior and error associated with each method in connection with typical analysis approaches. We also show implementation strategies for those methods, including how an implicit midpoint method solution can be generated from a trapezoidal method solution and vice versa. Finally, we present some empirical analysis of the behavior of each method for a simple diode clipper circuit and provide an approach to help interpret their relative performance and how to pick the more appropriate method depending on desirable properties. The presented tools are also intended as a general approach to interpret the performance of discretization approaches at large in the context of fixed-rate simulation.
Download Morph: Timbre Hybridization Tools Based on Frequency Domain Processing
This paper presents a hybridization method using Morph, a sound timbre hybridization and modeling software running on the Windows 95 platform. Elaboration occurs in Fourier space and is based on analysis/re-synthesis operations through FFT and FFT-1. The hybridization method works through the segmentation of two starting spectra in zones centered on the energy peaks. Each identified spectral zone, is numbered in increasing order so that a matching can be established between pairs of zones with the same value during re-synthesis. A full description of the Morph elaboration performance includes cross-synthesis, timbre hybridization, harmonic/inharmonic component separation and filtering. An initial catalogue of hybrid sounds has been compiled using this system, in order to tackle hybridization problems in an organic and systematic manner. The criteria used for the drafting and organization of the catalogue are discussed in the latter part of this paper.
Download Low-Cost Geometry-Based Acoustic Rendering
In this paper we propose a new sound rendering algorithm that allows the listener to move within a dinamic acoustic environment. The main goal of this work is to implement a real-time sound rendering software for Virtal Reality applications, which runs on lowcost platforms. The resulting numeric structure is a recursive filter able to efficiently simulate the impulse response of a large room.
Download Non-Iterative Schemes for the Simulation of Nonlinear Audio Circuits
In this work, a number of numerical schemes are presented in the context of virtual-analog simulation. The schemes are linearlyimplicit in character, and hence directly solvable without iterative methods. Schemes of increasing order of accuracy are constructed, and convergence and stability conditions are proven formally. The schemes are able to handle stiff problems very efficiently, because of their fast update, and can be run at higher sample rates to reduce aliasing. The cases of the diode clipper and ring modulator are investigated in detail, including several numerical examples.
Download Quality Diversity for Synthesizer Sound Matching
It is difficult to adjust the parameters of a complex synthesizer to create the desired sound. As such, sound matching, the estimation of synthesis parameters that can replicate a certain sound, is a task that has often been researched, utilizing optimization methods such as genetic algorithm (GA). In this paper, we introduce a novelty-based objective for GA-based sound matching. Our contribution is two-fold. First, we show that the novelty objective is able to improve the quality of sound matching by maintaining phenotypic diversity in the population. Second, we introduce a quality diversity approach to the problem of sound matching, aiming to find a diverse set of matching sounds. We show that the novelty objective is effective in producing high-performing solutions that are diverse in terms of specified audio features. This approach allows for a new way of discovering sounds and exploring the capabilities of a synthesizer.