Download Physical Modeling of the MXR Phase 90 Guitar Effect Pedal In this study, a famous boxed effect pedal, also called stompbox, for electrical guitars is analyzed and simulated. The nodal DK method is used to create a non-linear state-space system with Matlab as a physical model for the MXR Phase 90 guitar effect pedal. A crucial component of the effect are Junction Field Effect Transistors (JFETs) which are used as variable resistors to dynamically vary the phase-shift characteristic of an allpass-filter cascade. So far, virtual analog modeling in the context of audio has mainly been applied to diode-clippers and vacuum tube circuits. This work shows an efficient way of describing the nonlinear behavior of JFETs, which are wide-spread in audio devices. To demonstrate the applicability of the proposed physical model, a real-time VST audio plug-in was implemented.
Download A Physically-Informed, Circuit-Bendable, Digital Model of the Roland TR-808 Bass Drum Circuit We present an analysis of the bass drum circuit from the classic Roland TR-808 Rhythm Composer, based on physical models of the device’s many sub-circuits. A digital model based on this analysis (implemented in Cycling 74’s Gen˜) retains the salient features of the original and allows accurate emulation of circuit-bent modifications—complicated behavior that is impossible to capture through black-box modeling or structured sampling. Additionally, this analysis will clear up common misconceptions about the circuit, support the design of further drum machine modifications, and form a foundation for circuit-based musicological inquiry into the history of analog drum machines.
Download An Energy Conserving Finite Difference Scheme for the Simulation of Collisions in Snare Drums In this paper, a physics-based model for a snare drum will be discussed, along with its finite difference simulation. The interactions between a mallet and the membrane and between the snares and the membrane will be described as perfectly elastic collisions. A novel numerical scheme for the implementation of collisions will be presented, which allows a complete energy analysis for the whole system. Viscothermal losses will be added to the equation for the 3D wave propagation. Results from simulations and sound examples will be presented.
Download Finite Volume Perspectives on Finite Difference Schemes and Boundary Formulations for Wave Simulation Time-domain finite difference (FD) and digital waveguide mesh (DWM) methods have seen extensive exploration as techniques for physical modelling sound synthesis and artificial reverberation. Various formulations of these methods have been unified under the FD framework, but many discrete boundary models important in room acoustics applications have not been. In this paper, the finite volume (FV) framework is used to unify various FD and DWM topologies, as well as associated boundary models. Additional geometric insights on existing stability conditions provide guidance into the FV meshing pre-processing step necessary for the acoustic modelling of irregular and realistic room geometries. DWM “1-D” boundary terminations are shown, through an equivalent FV formulation, to have a consistent multidimensional interpretation that is approximated to second-order accuracy, however the geometry and wall admittances being approximated may vary from what is desired. It is also shown that certain re-entrant corner configurations can lead to instabilities and an alternative stable update is provided for one problematic configuration.
Download Finite Difference Schemes on Hexagonal Grids for Thin Linear Plates with Finite Volume Boundaries The thin plate is a key structure in various musical instruments, including many percussion instruments and the soundboard of the piano, and also is the mechanism underlying electromechanical plate reverberation. As such, it is a suitable candidate for physical modelling approaches to audio effects and sound synthesis, such as finite difference methods—though great attention must be paid to the problem of numerical dispersion, in the interest of reducing perceptual artefacts. In this paper, we present two finite difference schemes on hexagonal grids for such a thin plate system. Numerical dispersion and computational costs are analysed and compared to the standard 13-point Cartesian scheme. An equivalent finite volume scheme can be related to the 13-point Cartesian scheme and a 19-point hexagonal scheme, allowing for fitted boundary conditions of the clamped type. Theoretical modes for a clamped circular plate are compared to simulations. It is shown that better agreement is obtained for the hexagonal scheme than the Cartesian scheme.
Download Onset Time Estimation for the Analysis of Percussive Sounds using Exponentially Damped Sinusoids Exponentially damped sinusoids (EDS) model-based analysis of sound signals often requires a precise estimation of initial amplitudes and phases of the components found in the sound, on top of a good estimation of their frequencies and damping. This can be of the utmost importance in many applications such as high-quality re-synthesis or identification of structural properties of sound generators (e.g. a physical coupling of vibrating devices). Therefore, in those specific applications, an accurate estimation of the onset time is required. In this paper we present a two-step onset time estimation procedure designed for that purpose. It consists of a “rough" estimation using an STFT-based method followed by a time-domain method to “refine" the previous results. Tests carried out on synthetic signals show that it is possible to estimate onset times with errors as small as 0.2ms. These tests also confirm that operating first in the frequency domain and then in the time domain allows to reach a better resolution vs. speed compromise than using only one frequency-based or one time-based onset detection method. Finally, experiments on real sounds (plucked strings and actual percussions) illustrate how well this method performs in more realistic situations.
Download Declaratively Programmable Ultra Low-Latency Audio Effects Processing on FPGA WaveCore is a coarse-grained reconfigurable processor architecture, based on data-flow principles. The processor architecture consists of a scalable and interconnected cluster of Processing Units (PU), where each PU embodies a small floating-point RISC processor. The processor has been designed in technology-independent VHDL and mapped on a commercially available FPGA development platform. The programming methodology is declarative, and optimized to the application domain of audio and acoustical modeling. A benchmark demonstrator algorithm (guitar-model, comprehensive effects-gear box, and distortion/cabinet model) has been developed and applied to the WaveCore development platform. The demonstrator algorithm proved that WaveCore is very well suited for efficient modeling of complex audio/acoustical algorithms with negligible latency and virtually zero jitter. An experimental Faust-to-WaveCore compiler has shown the feasibility of automated compilation of Faust code to the WaveCore processor target. Keywords: ultra-low latency, zero-jitter, coarse-grained reconfigurable computing, declarative programming, automated manycore compilation, Faust-compatible, massively-parallel
Download Numerical Simulation of String/Barrier Collisions: The Fretboard Collisions play a major role in various models of musical instruments; one particularly interesting case is that of the guitar fretboard, the subject of this paper. Here, the string is modelled including effects of tension modulation, and the distributed collision both with the fretboard and individual frets, and including both effects of free string vibration, and under finger-stopped conditions, requiring an additional collision model. In order to handle multiple distributed nonlinearities simultaneously, a finite difference time domain method is developed, with a penalty potential allowing for a convenient model of collision within a Hamiltonian framework, allowing for the construction of stable energy-conserving methods. Implementation details are discussed, and simulation results are presented illustrating a variety of features of such a model.
Download A Comparison of Extended Source-Filter Models for Musical Signal Reconstruction Recently, we have witnessed an increasing use of the sourcefilter model in music analysis, which is achieved by integrating the source filter model into a non-negative matrix factorisation (NMF) framework or statistical models. The combination of the source-filter model and NMF framework reduces the number of free parameters needed and makes the model more flexible to extend. This paper compares four extended source-filter models: the source-filter-decay (SFD) model, the NMF with timefrequency activations (NMF-ARMA) model, the multi-excitation (ME) model and the source-filter model based on β-divergence (SFbeta model). The first two models represent the time-varying spectra by adding a loss filter and a time-varying filter, respectively. The latter two are extended by using multiple excitations and including a scale factor, respectively. The models are tested using sounds of 15 instruments from the RWC Music Database. Performance is evaluated based on the relative reconstruction error. The results show that the NMF-ARMA model outperforms other models, but uses the largest set of parameters.
Download Sinusoidal Synthesis Method using a Force-based Algorithmm In this paper we propose a synthesis method using a force-based algorithm to control frequencies of multiple sine waves. In order to implement this synthesis method, we analyze an existing sound source using a fast Fourier transform (FFT). Spectral peaks which have large magnitudes are regarded as heavy partials and assigned large attractive forces. A few hundred sine waves with stationary amplitudes are placed in a frequency space on which forces generated in the analysis phase are applied. The frequencies of the partials gravitate to the nearest peak of the reference spectrum from the source sound. As more sine waves are combined at the large peaks, the sound synthesized by the partials gradually transforms into the reference spectrum. In order to prevent the frequencies of the partials from gravitating onto localized peaks, each partial is assigned a repulsive force against all others. Through successful control of these attractive and repulsive forces, roughness and speed variation of the synthesis can be achieved. Moreover, by increasing or decreasing the number of partials according to the total amplitude of the source sound, amplitude envelope following is achieved.