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.
Download Chromax, the Other Side of the Spectral Delay Between Signal Processing and Composition
Spectral delays have been used for a long time as a way to colour and shape spectral characteristics of sound. Most of available software is controlled by drawing an envelope on a window that represents spectral bins, and by setting a maximum delay time. Despite its comfort, such a simplistic approach does not imply any methods for allowing symbolic manipulations on spectral data that are often required by composers and sound designers. Chromax proposes an alternative dynamic parameterization of spectral delays, allowing fine and complex compositional manipulations. It implements a bin-synchronous spectral processing using the new Gen~ technology available in Max6 [1], and provides algorithms to dynamically specify a filter, a delay and a feedback level for each bin of a processed sound.
Download Analysis/Synthesis Using Time-Varying Windows and Chirped Atoms
A common assumption that is often made regarding audio signals is that they are short-term stationary. In other words, it is typically assumed that the statistical properties of audio signals change slowly enough that they can be considered nearly constant over a short interval. However, using a fixed analysis window (which is typical in practice) we have no way to change the analysis parameters over time in order to track the slowly evolving properties of the audio signal. For example, while a long window may be appropriate for analyzing tonal phenomena it will smear subsequent note onsets. Furthermore, the audio signal may not be completely stationary over the duration of the analysis window. This is often true of sounds containing glissando, vibrato, and other transient phenomena. In this paper we build upon previous work targeted at non-stationary analysis/synthesis. In particular, we discuss how to simultaneously adapt the window length and the chirp rate of the analysis frame in order to maximally concentrate the spectral energy. This is done by a) finding the analysis window that leads to the minimum entropy spectrum; and, b) estimating the chirp rate using the distribution derivative method. We also discuss a fast method of analysis/synthesis using the fan-chirp transform and overlap-add. Finally, we analyze several real and synthetic signals and show a qualitative improvement in the spectral energy concentration.
Download On the Modeling of Sound Textures Based on the STFT Representation
Sound textures are often noisy and chaotic. The processing of these sounds must be based on the statistics of its corresponding time-frequency representation. In order to transform sound textures with existing mechanisms, a statistical model based on the STFT representation is favored. In this article, the relation between statistics of a sound texture and its time-frequency representation is explored. We proposed an algorithm to extract and modify the statistical properties of a sound texture based on its STFT representation. It allows us to extract the statistical model of a sound texture and resynthesise the sound texture after modifications have been made. It could also be used to generate new samples of the sound texture from a given sample. The results of the experiment show that the algorithm is capable of generating high quality sounds from an extracted model. This result could serve as a basis for transformations like morphing or high-level control of sound textures.