Download Block-oriented modeling of distortion audio effects using iterative minimization Virtual analog modeling is the process of digitally recreating an analog device. This study focuses on analog distortion pedals for guitarists, which are categorized as stompboxes, because the musician turns them on and off by stepping on the switch. While some of the current digital models of distortion effects are circuit-based, this study uses a signal-based approach to identify the device under test (DUT). An algorithm to identify any distortion effect pedal in any given setting by input-output (I/O) measurements is proposed. A parametric block-oriented Wiener-Hammerstein model for distortion effects and the corresponding iterative error minimization procedure are introduced. The algorithm is implemented in Matlab and uses the Levenberg-Marquardt minimization procedure with boundaries for the parameters.
Download Generalizing Root Variable Choice in Wave Digital Filters with Grouped Nonlinearities Previous grouped-nonlinearity formulations for Wave Digital Filter (WDF) modeling of nonlinear audio circuits assumed that nonlinear (NL) devices with memoryless voltage–current characteristics were modeled as voltage-controlled current sources (VCCSs). These formulations cannot accommodate nonlinear devices whose equations cannot be written as NL VCCSs, and they cannot accommodate circuits with cutsets composed entirely of current sources (including NL VCCSs). In this paper we generalize independent and dependent variable choice at the root of WDF trees to accommodate both these cases, and review two graph theorems for avoiding forbidden cutsets and loops in general.
Download Modal Parameter Tracking for Shape-Changing Geometric Objects For interactive sound synthesis, we would like to change the shape of a finite element model of an instrument and rapidly hear how the sound changes. Using modal synthesis methods, we would need to compute a new modal decomposition with each change in the geometry, making the analysis too slow for interactive use. However, by using modes computed for one geometry to estimate the frequencies for nearby geometries, we can hear much more quickly how changing the instrument shape changes the sound. In this paper, we describe how to estimate resonant frequencies of an instrument by combining information about the modes of two similar instruments. We also describe the balance between computational speed and accuracy of the computed resonances.
Download Consistency of Timbre Patterns in Expressive Music Performance Musical interpretation is an intricate process due to the interaction of the musician’s gesture and the physical possibilities of the instrument. From a perceptual point of view, these elements induce variations in rhythm, acoustical energy and timbre. This study aims at showing the importance of timbre variations as an important attribute of musical interpretation. For this purpose, a general protocol aiming at emphasizing specific timbre patterns from the analysis of recorded musical sequences is proposed. An example of the results obtained by analyzing clarinet sequences is presented, showing stable timbre variations and their correlations with both rhythm and energy deviations.
Download Fully-Implicit Algebro-Differential Parametrization of Circuits This paper is concerned with the conception of methods tailored
for the numerical simulation of power-balanced systems that are
well-posed but implicitly described. The motivation is threefold:
some electronic components (such as the ideal diode) can only
be implicitly described, arbitrary connection of components can
lead to implicit topological constraints, finally stable discretization
schemes also lead to implicit algebraic equations.
In this paper we start from the representation of circuits using a
power-balanced Kirchhoff-Dirac structure, electronic components
are described by a local state that is observed through a pair of
power-conjugated algebro-differential operators (V, I) to yield the
branch voltages and currents, the arc length is used to parametrize
switching and non-Lipschitz components, and a power balanced
functional time-discretization is proposed. Finally, the method is
illustrated on two simple but non-trivial examples.
Download Fourth-Order and Optimised Finite Difference Schemes for the 2-D Wave Equation This paper investigates some fourth-order accurate explicit finite difference schemes for the 2-D wave equation obtained using 13-, 17-, 21-, and 25-point discrete Laplacians. Optimisation is conducted in order to minimise numerical dispersion and computational costs. New schemes are presented that are more computationally efficient than nine-point explicit schemes at maintaining less than one percent wave speed error up to some critical frequency. Simulation results are presented.
Download WDF Modeling of a Korg MS-50 Based Non-linear Diode Bridge VCF The voltage-controlled low-pass filter of the Korg MS-50 synthesizer is built around a non-linear diode bridge as the cutoff frequency control element, which greatly contributes to the sound of this vintage synthesizer. In this paper, we introduce the overall filter circuitry and give an in-depth analysis of this diode bridge. It is further shown how to turn the small signal equivalence circuit of the bridge into the necessary two-resistor configuration to uncover the underlying Sallen-Key structure. In a second step, recent advances in the field of WDFs are used to turn a simplified version of the circuit into a virtual-analog model. This model is then examined both in the small-signal linear domain as well as in the non-linear region with inputs of different amplitudes and frequencies to characterize the behavior of such diode bridges as cutoff frequency control elements.
Download A Modal Approach to the Numerical Simulation of a String Vibrating Against an Obstacle: Applications to Sound Synthesis A number of musical instruments (electric basses, tanpuras, sitars...) have a particular timbre due to the contact between a vibrating string and an obstacle. In order to simulate the motion of such a string with the purpose of sound synthesis, various technical issues have to be resolved. First, the contact phenomenon, inherently nonlinear and producing high frequency components, must be described in a numerical manner that ensures stability. Second, as a key ingredient for sound perception, a fine-grained frequencydependent description of losses is necessary. In this study, a new conservative scheme based on a modal representation of the displacement is presented, allowing the simulation of a stiff, damped string vibrating against an obstacle with an arbitrary geometry. In this context, damping parameters together with eigenfrequencies of the system can be adjusted individually, allowing for complete control over loss characteristics. Two cases are then numerically investigated: a point obstacle located in the vicinity of the boundary, mimicking the sound of the tanpura, and then a parabolic obstacle for the sound synthesis of the sitar.
Download Resolving Grouped Nonlinearities in Wave Digital Filters using Iterative Techniques In this paper, iterative zero-finding techniques are proposed to resolve groups of nonlinearities occurring in Wave Digital Filters. Two variants of Newton’s method are proposed and their suitability towards solving the grouped nonlinearities is analyzed. The feasibility of the approach with implications for WDFs containing multiple nonlinearities is demonstrated via case studies investigating the mathematical properties and numerical performance of reference circuits containing diodes and transistors; asymmetric and symmetric diode clippers and a common emitter amplifier.
Download Application of Raster Scanning Method to Image Sonification, Sound Visualization, Sound Analysis and Synthesis Raster scanning is a technique for generating or recording a video image by means of a line-by-line sweep, tantamount to a data mapping scheme between one and two dimensional spaces. While this geometric structure has been widely used on many data transmission and storage systems as well as most video displaying and capturing devices, its application to audio related research or art is rare. In this paper, a data mapping mechanism of raster scanning is proposed as a framework for both image sonification and sound visualization. This mechanism is simple, and produces compelling results when used for sonifying image texture and visualizing sound timbre. In addition to its potential as a cross modal representation, its complementary and analogous property can be applied sequentially to create a chain of sonifications and visualizations using digital filters, thus suggesting a useful creative method of audio processing. Special attention is paid to the rastrogram - raster visualization of sound - as an intuitive visual interface to audio data. In addition to being an efficient means of sound representation that provides meaningful display of significant auditory features, the rastrogram is applied to the area of sound analysis by visualizing characteristics of loop filters used for a Karplus-Strong model. A new sound synthesis method based on texture analysis/synthesis of the rastrogram is also suggested.