Download An Explorative String-bridge-plate Model with Tunable Parameters The virtual exploration of the domain of mechano-acoustically produced sound and music is a long-held aspiration of physical modelling. A physics-based algorithm developed for this purpose combined with an interface can be referred to as a virtual-acoustic instrument; its design, formulation, implementation, and control are subject to a mix of technical and aesthetic criteria, including sonic complexity, versatility, modal accuracy, and computational efficiency. This paper reports on the development of one such system, based on simulating the vibrations of a string and a plate coupled via a (nonlinear) bridge element. Attention is given to formulating and implementing the numerical algorithm such that any of its parameters can be adjusted in real-time, thus facilitating musician-friendly exploration of the parameter space and offering novel possibilities regarding gestural control. Simulation results are presented exemplifying the sonic potential of the string-bridgeplate model (including bridge rattling and buzzing), and details regarding efficiency, real-time implementation and control interface development are discussed.
Download Latent Force Models for Sound: Learning Modal Synthesis Parameters and Excitation Functions from Audio Recordings Latent force models are a Bayesian learning technique that combine physical knowledge with dimensionality reduction — sets of coupled differential equations are modelled via shared dependence on a low-dimensional latent space. Analogously, modal sound synthesis is a technique that links physical knowledge about the vibration of objects to acoustic phenomena that can be observed in data. We apply latent force modelling to sinusoidal models of audio recordings, simultaneously inferring modal synthesis parameters (stiffness and damping) and the excitation or contact force required to reproduce the behaviour of the observed vibrational modes. Exposing this latent excitation function to the user constitutes a controllable synthesis method that runs in real time and enables sound morphing through interpolation of learnt parameters.
Download A Numerical Scheme for Various Nonlinear Forces, Including Collisions, Which Does Not Require an Iterative Root Finder Nonlinear forces are ubiquitous in physical systems, and of prominent importance in musical acoustics. Though many models exist to describe such forces, in most cases the associated numerical schemes rely on iterative root finding methods, such as NewtonRaphson or gradient descent, which are computationally expensive and which therefore could represent a computational bottleneck. In this paper, a model for a large class of nonlinear forces is presented, and a novel family of energy-conserving finite difference schemes given. The schemes only require the evaluation of the roots of a quadratic function. A few applications in the lumped case are shown, and the robustness and accuracy of the scheme tested.
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 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 Simulating the Friction Sounds Using a Friction-based Adhesion Theory Model Synthesizing a friction sound of deformable objects by a computer is challenging. We propose a novel physics-based approach to synthesize friction sounds based on dynamics simulation. In this work, we calculate the elastic deformation of an object surface when the object comes in contact with other objects. The principle of our method is to divide an object surface into microrectangles. The deformation of each microrectangle is set using two assumptions: the size of a microrectangle (1) changes by contacting other object and (2) obeys a normal distribution. We consider the sound pressure distribution and its space spread, consisting of vibrations of all microrectangles, to synthesize a friction sound at an observation point. We express the global motions of an object by position based dynamics where we add an adhesion constraint. Our proposed method enables the generation of friction sounds of objects in different materials by regulating the initial value of microrectangular parameters.
Download Modal Audio Effects: A Carillon Case Study Modal representations—decomposing the resonances of objects into their vibrational modes has historically been a powerful tool for studying and synthesizing the sounds of physical objects, but it also provides a flexible framework for abstract sound synthesis. In this paper, we demonstrate a variety of musically relevant ways to modify the model upon resynthesis employing a carillon model as a case study. Using a set of audio recordings of the sixty bells of the Robert and Ann Lurie Carillon recorded at the University of Michigan, we present a modal analysis of these recordings, in which we decompose the sound of each bell into a sum of decaying sinusoids. Each sinusoid is characterized by a modal frequency, exponential decay rate, and initial complex amplitude. This analysis yields insight into the timbre of each individual bell as well as the entire carillon as an ensemble. It also yields a powerful parametric synthesis model for reproducing bell sounds and bell-based audio effects.
Download On Iterative Solutions for Numerical Collision Models Nonlinear interactions between different parts of musical instruments present several challenges regarding the formulation of reliable and efficient numerical sound synthesis models. This paper focuses on a numerical collision model that incorporates impact damping. The proposed energy-based approach involves an iterative solver for the solution of the nonlinear system equations. In order to ensure the efficiency of the presented algorithm a bound is derived for the maximum number of iterations required for convergence. Numerical results demonstrate energy conservation as well as convergence within a small number of iterations, which is usually much lower than the predicted bound. Finally, an application to music acoustics, involving a clarinet simulation, shows that including a loss mechanism during collisions may have a significant effect on sound production.
Download Live Convolution with Time-variant Impulse Response This paper describes a method for doing convolution of two live signals, without the need to load a time-invariant impulse response (IR) prior to the convolution process. The method is based on stepwise replacement of the IR in a continuously running convolution process. It was developed in the context of creative live electronic music performance, but can be applied to more traditional use cases for convolution as well. The process allows parametrization of the convolution parameters, by way of real-time transformations of the IR, and as such can be used to build parametric convolution effects for audio mixing and spatialization as well.