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 A Stable Acoustic Impedance Model of the Clarinet using Digital Waveguides Digital waveguide (DW) modeling techniques are typically associated with a traveling-wave decomposition of wave variables and a “reflection function” approach to simulating acoustic systems. As well, it is often assumed that inputs and outputs to/from these systems must be formulated in terms of traveling-wave variables. In this paper, we provide a tutorial review of DW modeling of acoustic structures to show that they can easily accommodate physical input and output variables. Under certain constraints, these formulations reduce to simple “Schroeder reverb-like” computational structures. We also present a stable single-reed filter model that allows an explicit solution at the reed / air column junction. A clarinet-like system is created by combining the reed filter with a DW impedance model of a cylindrical air column.
Download Digital Synthesis Models of Clarinet-Like Instruments Including Nonlinear Losses in the Resonator This paper presents a real-time algorithm for the synthesis of reed instruments, taking into account nonlinear losses at the first open tonehole. The physical model on which the synthesis model relies on is based on the experimental works of Dalmont et al. who have shown that for high pressure levels within the bore, an air jet obeying the Bernoulli flow model, hence acting as a nonlinear resistance, is created at the open end of the bore. We study the effect of these additional losses on the response of the bore to an acoustic flow impulse at different levels and on the self oscillations. We show that at low frequencies, these nonlinear losses are of the same order of magnitude than the viscothermal linear losses and modifie the functioning of the whole instrument. For real-time synthesis purposes, a simplified algorithm is proposed and compared to the more accurate model.
Download A Source Localization/Separation/Respatialization System Based on Unsupervised Classification of Interaural Cues In this paper we propose a complete computational system for Auditory Scene Analysis. This time-frequency system localizes, separates, and spatializes an arbitrary number of audio sources given only binaural signals. The localization is based on recent research frameworks, where interaural level and time differences are combined to derive a confident direction of arrival (azimuth) at each frequency bin. Here, the power-weighted histogram constructed in the azimuth space is modeled as a Gaussian Mixture Model, whose parameter structure is revealed through a weighted Expectation Maximization. Afterwards, a bank of Gaussian spatial filters is configured automatically to extract the sources with significant energy accordingly to a posterior probability. In this frequency-domain framework, we also inverse a geometrical and physical head model to derive an algorithm that simulates a source as originating from any azimuth angle.
Download Discretization of the '59 Fender Bassman Tone Stack The market for digital modeling guitar amplifiers requires that the digital models behave like the physical prototypes. A component of the iconic Fender Bassman guitar amplifier, the tone stack circuit, filters the sound of the electric guitar in a unique and complex way. The controls are not orthogonal, resulting in complicated filter coefficient trajectories as the controls are varied. Because of its electrical simplicity, the tone stack is analyzed symbolically in this work, and digital filter coefficients are derived in closed form. Adhering to the technique of virtual analog, this procedure results in a filter that responds to user controls in exactly the same way as the analog prototype. The general expressions for the continuous-time and discrete-time filter coefficients are given, and the frequency responses are compared for the component values of the Fender ’59 Bassman. These expressions are useful implementation and verification of implementations such as the wave digital filter.
Download Frequency-Dependent Boundary Condition for the 3-D Digital Waveguide Mesh The three-dimensional digital waveguide mesh is a method for modeling the propagation of sound waves in space. It provides a simulation of the state of the whole soundfield at discrete timesteps. The updating functions of the mesh can be formulated either using physical values of sound pressure or particle velocity, also called the Kirchhoff values, or using a wave decomposition of these instead. Computation in homogenous media is significantly lighter using Kirchhoff variables, but frequency-dependent boundary conditions are more easily defined with wave variables. In this paper a conversion method between these two variable types has been further simplified. Using the resulting structure, a novel method for defining the mesh boundaries with digital filters is introduced. With this new method, the reflection coefficients can be defined in a frequency-dependent manner at the boundaries of a Kirchhoff variable mesh. This leads to computationally lighter and more realistic simulations than previous solutions.
Download Robust Design of Very High-Order Allpass Dispersion Filters A nonparametric allpass filter design method is presented for matching a desired group delay as a function of frequency. The technique is useful in physical modeling synthesis of musical instruments and emulation of audio effects devices exhibiting dispersive wave propagation. While current group delay filter design methods suffer from numerical difficulties except at low filter orders, the technique presented here is numerically robust, producing an allpass filter in cascaded biquad form, and with the filter poles following a smooth loop within the unit circle. The technique was inspired by the observation that a pole-zero pair arranged in allpass form contributes exactly 2π radians to the integral of group delay around the unit circle, regardless of the (stable) pole location. To match a given group delay characteristic, the method divides the frequency axis into sections containing 2π total area under the desired group-delay curve, and assigns a polezero allpass pair to each. In this way, the method incorporates an order selection technique, and by adding a pure delay to the desired group delay, allows the trading of increased filter order for improved fit to the frequency-dependent group delay. Design examples are given for modeling the group delay of a dispersive string (such as a piano string), and a dispersive spring, such as in a spring reverberator.
Download Prepared Piano Sound Synthesis A sound synthesis algorithm which simulates and extends the behaviour of the acoustic prepared piano is presented. The algorithm is based on a finite difference approximation to multiple stiff string vibration, including an excitation method (a hammer) as well as several connected preparation elements, modeled as lumped nonlinearities. Numerical issues and implementation details are discussed, and sound examples are presented.
Download A Stochastic State-Space Phase Vocoder for Synthesis of Roughness This paper presents an implementation of the phase vocoder within a Gaussian state-space framework. Rather than formulate the problem as a deterministic evolution of frequencies centered around a given bin, this evolution is treated stochastically by introducing noise into the dynamics matrix of the recursive state equation. This produces effects on the roughness of the input sound, which vary depending on the position within the matrix where the noise is added, how it is propagated throughout the matrix and further by the variance of the noise input.
Download Examining Design Goals of Digital Musical Instruments This paper describes the adaptation of an existing model of human information processing for the categorization of digital musical instruments in terms of performance context and behavior. It further presents a visualization intended to aid the analysis of existing DMIs and the design of new devices. Three new interfaces constructed by the authors are examined within this framework to illustrate its utility.