Download Articulatory vocal tract synthesis in Supercollider The APEX system [1] enables vocal tract articulation using a reduced set of user controllable parameters by means of Principal Component Analysis of X-ray tract data. From these articulatory profiles it is then possible to calculate cross-sectional area function data that can be used as input to a number of articulatory based speech synthesis algorithms. In this paper the Kelly-Lochbaum 1-D digital waveguide vocal tract is used, and both APEX control and synthesis engine have been implemented and tested in SuperCollider. Accurate formant synthesis and real-time control are demonstrated, although for multi-parameter speech-like articulation a more direct mapping from tract-to-synthesizer tube sections is needed. SuperCollider provides an excellent framework for the further exploration of this work.
Download Digitally Moving An Electric Guitar Pickup This paper describes a technique to transform the sound of an arbitrarily selected magnetic pickup into another pickup selection on the same electric guitar. This is a first step towards replicating an arbitrary electric guitar timbre in an audio recording using the signal from another guitar as input. We record 1458 individual notes from the pickups of a single guitar, varying the string, fret, plucking position, and dynamics of the tones in order to create a controlled dataset for training and testing our approach. Given an input signal and a target signal, a least squares estimator is used to obtain the coefficients of a finite impulse response (FIR) filter to match the desired magnetic pickup position. We use spectral difference to measure the error of the emulation, and test the effects of independent variables fret, dynamics, plucking position and repetition on the accuracy. A small reduction in accuracy was observed for different repetitions; moderate errors arose when the playing style (plucking position and dynamics) were varied; and there were large differences between output and target when the training and test data comprised different notes (fret positions). We explain results in terms of the acoustics of the vibrating strings.
Download Real-time 3D Ambisonics using Faust, Processing, Pure Data, and OSC This paper presents several digital signal processing (DSP) tools for the real-time synthesis of a 3D sound pressure field using Ambisonics technologies. The spatialization of monophonic signal or the reconstruction of natural 3D recorded sound pressure fields is considered. The DSP required to generate the loudspeaker signals is implemented using the FAUST programming language. FAUST enables and simplifies the compilation of the developed tools on several architectures and on different DSP tool format. In this paper, a focus is made on the near-field filters implementation which allows for the encoding of spherical waves with distance information. The gain variation with distance is also taken into account. The control of the synthesis can be made by software controllers or hardware controllers, such as joystick, by the mean of P URE DATA and O PEN S OUND C ONTROL (OSC) messages. A visual feedback tool using the P ROCESSING programming language is also presented in the most recent implementation. The aim of this research derives from a larger research project on physically-accurate sound field reproduction for simulators in engineering and industrial applications.
Download Improving the robustness of the iterative solver in state-space modelling of guitar distortion circuitry Iterative solvers are required for the discrete-time simulation of nonlinear behaviour in analogue distortion circuits. Unfortunately, these methods are often computationally too expensive for realtime simulation. Two methods are presented which attempt to reduce the expense of iterative solvers. This is achieved by applying information that is derived from the specific form of the nonlinearity. The approach is first explained through the modelling of an asymmetrical diode clipper, and further exemplified by application to the Dallas Rangemaster Treble Booster guitar pedal, which provides an initial perspective of the performance on systems with multiple nonlinearities.
Download Simulations of Nonlinear Plate Dynamics: An Accurate and Efficient Modal Algorithm This paper presents simulations of nonlinear plate vibrations in relation to sound synthesis of gongs and cymbals. The von Kármán equations are shown and then solved in terms of the modes of the associated linear system. The modal equations obtained constitute a system of nonlinearly coupled Ordinary Differential Equations which are completely general as long as the modes of the system are known. A simple second-order time-stepping integration scheme yields an explicit resolution algorithm with a natural parallel structure. Examples are provided and the results discussed.
Download Digitizing the Ibanez Weeping Demon Wah Pedal Being able to transform an analog audio circuit into a digital model is a big deal for musicians, producers, and circuit benders alike. In this paper, we address some of the issues that arise when attempting to make such a digital model. Using the canonical state variable filter as the main point of interest in our schematic, we will walk through the process of making a signal flow graph, obtaining a transfer function, and making a usable digital filter. Additionally, we will address an issue that is common throughout virtual analog literature; reducing the very large expressions for each of the filter coefficients. Using a novel factoring algorithm, we show that these expressions can be reduced from thousands of operations down to tens of operations.
Download Distortion and Pitch Processing Using a Modal Reverberator Architecture A reverberator based on a room response modal analysis is adapted to produce distortion, pitch and time manipulation effects, as well as gated and iterated reverberation. The so-called “modal reverberator” is a parallel collection of resonant filters, with resonance frequencies and dampings tuned to the modal frequencies and decay times of the space or object being simulated. Here, the resonant filters are implemented as cascades of heterodyning, smoothing, and modulation steps, forming a type of analysis/synthesis architecture. By applying memoryless nonlinearities to the modulating sinusoids, distortion effects are produced, including distortion without intermodulation products. By using different frequencies for the heterodyning and associated modulation operations, pitch manipulation effects are generated, including pitch shifting and spectral “inversion.” By resampling the smoothing filter output, the signal time axis is stretched without introducing pitch changes. As these effects are integrated into a reverberator architecture, reverberation controls such as decay time can be used produce novel effects having some of the sonic characteristics of reverberation.
Download Frequency estimation of the first pinna notch in Head-Related Transfer Functions with a linear anthropometric model The relation between anthropometric parameters and Head-Related Transfer Function (HRTF) features, especially those due to the pinna, are not fully understood yet. In this paper we apply signal processing techniques to extract the frequencies of the main pinna notches (known as N1 , N2 , and N3 ) in the frontal part of the median plane and build a model relating them to 13 different anthropometric parameters of the pinna, some of which depend on the elevation angle of the sound source. Results show that while the considered anthropometric parameters are not able to approximate with sufficient accuracy neither the N2 nor the N3 frequency, eight of them are sufficient for modeling the frequency of N1 within a psychoacoustically acceptable margin of error. In particular, distances between the ear canal and the outer helix border are the most important parameters for predicting N1 .
Download Design principles for lumped model discretisation using Möbius transforms Computational modelling of audio systems commonly involves discretising lumped models. The properties of common discretisation schemes are typically derived through analysis of how the imaginary axis on the Laplace-transform s-plane maps onto the Ztransform z-plane and the implied stability regions. This analysis ignores some important considerations regarding the mapping of individual poles, in particular the case of highly-damped poles. In this paper, we analyse the properties of an extended class of discretisations based on Möbius transforms, both as mappings and discretisation schemes. We analyse and extend the concept of frequency warping, well-known in the context of the bilinear transform, and we characterise the relationship between the damping and frequencies of poles in the s- and z-planes. We present and analyse several design criteria (damping monotonicity, stability) corresponding to desirable properties of the discretised system. Satisfying these criteria involves selecting appropriate transforms based on the pole structure of the system on the s-plane. These theoretical developments are finally illustrated on a diode clipper nonlinear model.