Download Comparison of Germanium Bipolar Junction Transistor Models for Real-time Circuit Simulation The Ebers-Moll model has been widely used to represent Bipolar Junction Transistors (BJTs) in Virtual Analogue (VA) circuits. An investigation into the validity of this model is presented in which the Ebers-Moll model is compared to BJT models of higher complexity, introducing the Gummel-Poon model to the VA field. A comparison is performed using two complementary approaches: on fit to measurements taken directly from BJTs, and on application to physical circuit models. Targeted parameter extraction strategies are proposed for each model. There are two case studies, both famous vintage guitar effects featuring germanium BJTs. Results demonstrate the effects of incorporating additional complexity into the component model, weighing the trade-off between differences in the output and computational cost.
Download Physically-based synthesis of nonlinear circular membranes This paper investigates the properties of a recently proposed physical model of nonlinear tension modulation effects in a struck circular membrane. The model simulates dynamic variations of tension (and consequently of partial frequencies) due to membrane stretching during oscillation, and is based on a more general theory of geometric nonlinearities in elastic plates. The ability of the nonlinear membrane model to simulate real-world acoustic phenomena is assessed here through resynthesis of recorded membrane (rototom) sounds. The effects of air loading and tension modulation in the recorded sounds are analyzed, and model parameters for resynthesis are consequently estimated. The example reported in the paper show that the model is able to accurately simulate the analyzed rototom sounds.
Download Physical Modelling of a Wah-wah Effect Pedal as a Case Study for Application of the Nodal DK Method to Circuits with Variable Parts The nodal DK method is a systematic way to derive a non-linear state-space system as a physical model for an electrical circuit. Unfortunately, calculating the system coefficients requires inversion of a relatively large matrix. This becomes a problem when the system changes over time, requiring continuous recomputation of the coefficients. In this paper, we present an extension of the DK method to more efficiently handle variable circuit elements. The method is exemplified with the Dunlop Crybaby wah-wah effect pedal, as the continuous change of the potentiometer position is an extremely important aspect of the wah-wah effect.
Download A Proposal for using SMS for Expression Modeling Spectral models have proven to be a successful method for analyzing and re-synthesizing natural and acoustic sounds, to the extent that a musical phrase can also be modeled in order to extract performance parameters. This paper suggests various parameters which are embedded in the spectral analysis or .sms file and proposes some methods which can be used for expression modeling based upon compositional, perceptive, and cognition approaches. The focus is on achieving the means to construct a translation algorithm which the composer can use as a tool to analyze expressive material such as a musical phrase or a spoken sentence of text, and apply detected parameters to the vectors of a physical model or a synthesis algorithm..
Download A Spatial Interface for Audio and Music Production In an effort to find a better suited interface for musical performance, a novel approach has been discovered and developed. At the heart of this approach is the concept of physical interaction with sound in space, where sound processing occurs at various 3D locations and sending sound signals from one area to another is based on physical models of sound propagation. The control is based on a gestural vocabulary that is familiar to users, involving natural spatial interaction such as translating, rotating, and pointing in 3-D. This research presents a framework to deal with realtime control of 3-D audio, and describes how to construct audio scenes to accomplish various musical tasks. The generality and effectiveness of this approach has enabled us to re-implement several conventional applications, with the benefit of a substantially more powerful interface, and has further led to the conceptualization of several novel applications.
Download Energy and Accuracy Issues in Numerical Simulations of a Non-linear Impact model A physically-based impact model – already known and exploited in the field of sound synthesis – is studied using both analytical tools and numerical simulations. It is shown that, for some regions of the parameter space, the trajectories of discretized systems may drift from analytically-derived curves. Some methods, based on enforcing numerical energy consistency, are suggested to improve the accuracy and stability of discrete-time systems.
Download Energy Shaping of a Softening Duffing Oscillator Using the Formalism of Port-Hamiltonian Systems This work takes place in the context of the development of an active control of instruments with geometrical nonlinearities. The study focuses on Chinese opera gongs that display a characteristic pitch glide in normal playing conditions. In the case of the xiaoluo gong, the fundamental mode of the instrument presents a softening behaviour (frequency glides upward when the amplitude decreases). Controlling the pitch glide requires a nonlinear model of the structure, which can be partially identified with experimental techniques that rely on the formalism of nonlinear normal modes. The fundamental nonlinear mode has been previously experimentally identified as a softening Duffing oscillator. This paper aims at performing a simulation of the control of the oscillator’s pitch glide. For this purpose, the study focuses on a single-degree-offreedom nonlinear mode described by a softening Duffing equation. This Duffing oscillator energy proves to be ill-posed - in particular, the energy becomes negative for large amplitudes of vibration, which is physically inconsistent. Then, the first step of the present study consists in redefining a new energetically well-posed model. In a second part, guaranteed-passive simulations using port-Hamiltonian formalism confirm that the new system is physically and energetically correct compared to the Duffing model. Third, the model is used for control issues in order to modify the softening or hardening behaviour of the fundamental pitch glide. Results are presented and prove the method to be relevant. Perspectives for experimental applications are finally exposed in the last section of the paper.
Download Modal Based Tanpura Simulation: Combining Tension Modulation and Distributed Bridge Interaction Techniques for the simulation of the tanpura have advanced significantly in recent years allowing numerically stable inclusion of bridge contact. In this paper tension modulation is added to a tanpura model containing a stiff lossy string, distributed bridge contact and the thread. The model is proven to be unconditionally stable and the numerical solver used has a unique solution as a result of choices made in the discretisation process. Effects due to the distribution of the bridge contact forces by comparison to a single point bridge and of introducing the tension modulation are studied in simulations. This model is intended for use in furthering the understanding of the physics of the tanpura and for informing the development of algorithms for sound synthesis of the tanpura and similar stringed instruments.
Download State of the Art in Sound Texture Synthesis The synthesis of sound textures, such as rain, wind, or crowds, is an important application for cinema, multimedia creation, games and installations. However, despite the clearly defined requirments of naturalness and flexibility, no automatic method has yet found widespread use. After clarifying the definition, terminology, and usages of sound texture synthesis, we will give an overview of the many existing methods and approaches, and the few available software implementations, and classify them by the synthesis model they are based on, such as subtractive or additive synthesis, granular synthesis, corpus-based concatenative synthesis, wavelets, or physical modeling. Additionally, an overview is given over analysis methods used for sound texture synthesis, such as segmentation, statistical modeling, timbral analysis, and modeling of transitions. 2
Download A Computational Model of the Hammond Organ Vibrato/Chorus using Wave Digital Filters We present a computational model of the Hammond tonewheel organ vibrato/chorus, a musical audio effect comprising an LC ladder circuit and an electromechanical scanner. We model the LC ladder using the Wave Digital Filter (WDF) formalism, and introduce a new approach to resolving multiple nonadaptable linear elements at the root of a WDF tree. Additionally we formalize how to apply the well-known warped Bilinear Transform to WDF discretization of capacitors and inductors and review WDF polarity inverters. To model the scanner we propose a simplified and physically-informed approach. We discuss the time- and frequency-domain behavior of the model, emphasizing the spectral properties of interpolation between the taps of the LC ladder.