Download A Physically-Constrained Source Model for FDTD Acoustic Simulation The Finite Difference Time Domain (FDTD) method is becoming increasingly popular for room acoustics simulation. Yet, the literature on grid excitation methods is relatively sparse, and source functions are traditionally implemented in a hard or additive form using arbitrarily-shaped functions which do not necessarily obey the physical laws of sound generation. In this paper we formulate a source function based on a small pulsating sphere model. A physically plausible method to inject a source signal into the grid is derived from first principles, resulting in a source with a nearflat spectrum that does not scatter incoming waves. In the final discrete-time formulation, the source signal is the result of passing a Gaussian pulse through a digital filter simulating the dynamics of the pulsating sphere, hence facilitating a physically correct means to design source functions that generate a prescribed sound field.
Download Potentiometer law modelling and identification for application in physics-based Virtual Analogue circuits Physical circuit models have an inherent ability to simulate the behaviour of user controls as exhibited by, for example, potentiometers. Working to accurately model the user interface of musical circuits, this work provides potentiometer ‘laws’ that fit to the underlying characteristics of linear and logarithmic potentiometers. A strategy of identifying these characteristics is presented, exclusively using input/output measurements and as such avoiding device disassembly. By breaking down the identification problem into one dimensional, search spaces characteristics are successfully identified. The proposed strategy is exemplified through a case study on the tone stack of the Big Muff Pi.
Download Quadratic Spline Approximation of the Contact Potential for Real-Time Simulation of Lumped Collisions in Musical Instruments Collisions are an integral part of the sound production mechanism in a wide variety of musical instruments. In physics-based realtime simulation of such nonlinear phenomena, challenges centred around efficient and accurate root-finding arise. Nonlinearly implicit schemes are normally ill-suited for real-time simulation as they rely on iterative solvers for root-solving. Explicit schemes overcome this issue at the cost of a slightly larger error for a given sample rate. In this paper, for the case of lumped collisions, an alternate approach is proposed by approximating the contact potential curve. The approximation is described, and is shown to lead to a non-iterative update for an energy-stable nonlinearly implicit scheme. The method is first tested on single mass-barrier collision simulations, and then employed in conjunction with a modal string model to simulate hammer-string and slide-string interaction. Results are discussed in comparison with existing approaches, and real-time feasibility is demonstrated.