Download Simulation of Textured Audio Harmonics Using Random Fractal Phaselets We present a method of simulating audio signals using the principles of random fractal geometry which, in the context of this paper, is concerned with the analysis of statistically self-affine ‘phaselets’. The approach is used to generate audio signals that are characterised by texture and timbre through the Fractal Dimension such as those associated with bowed stringed instruments. The paper provides a short overview on potential simulation methods using Artificial Neural Networks and Evolutionary Computing and on the problems associated with using a deterministic approach based on solutions to the acoustic wave equation. This serves to quantify the origins of the ‘noise’ associated with multiple scattering events that characterise texture and timbre in an audio signal. We then explore a method to compute the phaselet of a phase signal which is the primary phase function from which a phase signal is, to a good approximation, a periodic replica and show that, by modelling the phaselet as a random fractal signal, it can be characterised by the Fractal Dimension. The Fractal Dimension is then used to synthesise a phaselet from which the phase function is computed through multiple concatenations of the phaselet. The paper provides details of the principal steps associated with the method considered and examines some example results, providing a URL to m-coded functions for interested readers to repeat the results obtained and develop the algorithms further.
Download Source Filter Model For Expressive Gu-Qin Synthesis and its iOS App Gu-Qin as a venerable Chinese plucked-string instrument has its unique performance techniques and enchanting sounds. It is on the UNESCO Representative List of the Intangible Cultural Heritage of Humanity. It is one of the oldest Chinese solo instruments. The variation of Gu-Qin sound is so large that carefullydesigned controls of its computer synthesizer are necessary. We developed a parametric source-filter model for re-synthesizing expressive Gu-Qin notes. It is capable to cover as many as possible combinations of Gu-Qin’s performance techniques. In this paper, a brief discussion of Gu-Qin playing and its special tablature notation are made for understanding the relationship between its performance techniques and its sounds. This work includes a Gu-Qin’s musical notation system and a source-filter model based synthesizer. In addition, we implement an iOS app to demonstrate its low computation complexity and robustness. It is easy to perform improvisation of the sounds because of its friendly user interfaces.
Download Extended Source-Filter Model for Harmonic Instruments for Expressive Control of Sound Synthesis and Transformation In this paper we present a revised and improved version of a recently proposed extended source-filter model for sound synthesis, transformation and hybridization of harmonic instruments. This extension focuses mainly on the application for impulsively excited instruments like piano or guitar, but also improves synthesis results for continuously driven instruments including their hybrids. This technique comprises an extensive analysis of an instruments sound database, followed by the estimation of a generalized instrument model reflecting timbre variations according to selected control parameters. Such an instrument model allows for natural sounding transformations and expressive control of instrument sounds regarding its control parameters.
Download Bit Bending: an Introduction We introduce the technique of "Bit Bending," a particularly fertile technique for circuit bending which involves short circuits and manipulations upon digital serial information. We present a justification for computer modeling of circuit-bent instruments, with deference to the movement's aversion to "theory-true" design and associations with chance discovery [1]. To facilitate software modeling of Bit Bending, we also present a software library for modeling certain classes of digital integrated circuits. A synthesis architecture case study (frequency modulation via numerically controlled oscillators) demonstrates software modeling of Bit Bending in action.
Download Numerical Simulation of Spring Reverberation Virtual analog modeling of spring reverberation presents a challenging problem to the algorithm designer, regardless of the particular strategy employed. The difficulties lie in the behaviour of the helical spring, which, due to its inherent curvature, shows characteristics of both coherent and dispersive wave propagation. Though it is possible to emulate such effects in an efficient manner using audio signal processing constructs such as delay lines (for coherent wave propagation) and chains of allpass filters (for dispersive wave propagation), another approach is to make use of direct numerical simulation techniques, such as the finite difference time domain method (FDTD) in order to solve the equations of motion directly. Such an approach, though more computationally intensive, allows a closer link with the underlying model system— and yet, there are severe numerical difficulties associated with such designs, and in particular anomalous numerical dispersion, requiring some care at the design stage. In this paper, a complete model of helical spring vibration is presented; dispersion analysis from an audio perspective allows for model simplification. A detailed description of novel FDTD designs follows, with special attention is paid to issues such as numerical stability, loss modeling, numerical boundary conditions, and computational complexity. Simulation results are presented.
Download Fourth-Order and Optimised Finite Difference Schemes for the 2-D Wave Equation This paper investigates some fourth-order accurate explicit finite difference schemes for the 2-D wave equation obtained using 13-, 17-, 21-, and 25-point discrete Laplacians. Optimisation is conducted in order to minimise numerical dispersion and computational costs. New schemes are presented that are more computationally efficient than nine-point explicit schemes at maintaining less than one percent wave speed error up to some critical frequency. Simulation results are presented.
Download Parametric Audio Coding of Bass Guitar Recordings Using a Tuned Physical Modeling Algorithm In this paper, we propose a parametric audio coding framework that combines the analysis and re-synthesis of electric bass guitar recordings. In particular, an existing synthesis algorithm that incorporates 11 playing techniques is extended by two calibration algorithms. Both the temporal and spectral decay parameters as well as the inharmonicity coefficient are set according to the fretboard position on the instrument. Listening tests show that there is still a gap in perceptual quality between real-world instrument recordings and the re-synthesized versions. Due to this gap, the perceived improvement due to the model calibration is only small. Second, the listening tests reveal that the plucking styles are more important towards realistic synthesis results than expression styles.
Download 3D Particle Systems for Audio Applications Although particle systems are well know for their use in computer graphics, their application in sound is very rare or almost non-existent. This paper presents a conceptual model for the use of particle systems in audio applications, using a full rendering system with virtual microphones: several virtual particles are spread over a virtual 3D space, where each particle reproduces one of the available audio streams (or a modified version), and the overall sound is captured by virtual microphones. Such system can be used on several audio-related areas like sound design, 3D mixing, reverb/impulse response design, granular synthesis, audio up-mixing, and impulse response up-mixing.
Download Physically Informed Synthesis of Jackhammer Tool Impact Sounds This paper introduces a sound synthesis method for jackhammer tool impact sounds. The model is based on parallel waveguide models for longitudinal and transversal vibrations. The longitudinal sounds are produced using a comb filter that is tuned to match the longitudinal resonances of a steel bar. The dispersive transversal vibrations are produced using a comb filter which has a cascade of first-order allpass filters and time-varying feedback coefficient. The synthesis model is driven by an input generator unit that produces a train of Hann pulses at predetermined time-intervals. Each pulse has its amplitude modified slightly by a random process. For increased realism each impact is followed by a number of repetitive impacts with variable amplitude and time difference according to the initial pulse. The sound output of the model is realized by mixing both transversal and longitudinal signals and the effect is finalized by an equalizer.
Download Guitar Preamp Simulation Using Connection Currents This paper deals with a method of decomposition of a nonlinear audio circuit based on so called connection currents. These currents are used to connect inner blocks of the audio circuit with regards to preserve mutual interaction between adjoined blocks. Although this approach requires usage of numerical algorithm to solve the nonlinear equations, it reduces number of nonlinear equations to be solved if the solution of inner blocks is approximated while the accuracy of simulation is comparable to numerical solution of the whole nonlinear audio circuit.