Download Modal Audio Effects: A Carillon Case Study Modal representations—decomposing the resonances of objects into their vibrational modes has historically been a powerful tool for studying and synthesizing the sounds of physical objects, but it also provides a flexible framework for abstract sound synthesis. In this paper, we demonstrate a variety of musically relevant ways to modify the model upon resynthesis employing a carillon model as a case study. Using a set of audio recordings of the sixty bells of the Robert and Ann Lurie Carillon recorded at the University of Michigan, we present a modal analysis of these recordings, in which we decompose the sound of each bell into a sum of decaying sinusoids. Each sinusoid is characterized by a modal frequency, exponential decay rate, and initial complex amplitude. This analysis yields insight into the timbre of each individual bell as well as the entire carillon as an ensemble. It also yields a powerful parametric synthesis model for reproducing bell sounds and bell-based audio effects.
Download Pitch glide analysis and synthesis from Recorded Tones Pitch glide is an important effect that occurs in nearly all plucked string instruments. In essence, large amplitude waves traveling on a string during the note onset increases the string tension above its nominal value, and therefore cause the pitch to temporarily increase. Measurements are presented showing an exponential relaxation of all the partial frequencies to their nominal values with a time-constant related to the decay rate of transverse waves propagating on the string. This exponential pitch trajectory is supported by a simple physical model in which the increased tension is somewhat counterbalanced by the increased length of the string. Finally, a method for synthesizing the plucked string via a novel hybrid digital waveguide-modal synthesis model is presented with implementation details for time-varying resonators.
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 Two polarisation finite difference model of bowed strings with nonlinear contact and friction forces Recent bowed string sound synthesis has relied on physical modelling techniques; the achievable realism and flexibility of gestural control are appealing, and the heavier computational cost becomes less significant as technology improves. A bowed string is simulated in two polarisations by discretising the partial differential equations governing its behaviour, using the finite difference method; a globally energy balanced scheme is used, as a guarantee of numerical stability under highly nonlinear conditions. In one polarisation, a nonlinear contact model is used for the normal forces exerted by the dynamic bow hair, left hand fingers, and fingerboard. In the other polarisation, a force-velocity friction curve is used for the resulting tangential forces. The scheme update requires the solution of two nonlinear vector equations.Sound examples and video demonstrations are presented.
Download Advanced Fourier Decomposition for Realistic Drum Synthesis This paper presents a novel method of analysing drum sounds,
demonstrating that this can form the basis of a highly realistic synthesis technique for real-time use. The synthesis method can be
viewed as an extension of IFFT synthesis; here we exploit the fact
that audio signals can be recovered from solely the real component of their discrete Fourier transform (RDFT). All characteristics
of an entire drum sample can therefore be conveniently encoded
in a single, real-valued, frequency domain signal. These signals
are interpreted, incorporating the physics of the instrument, and
modelled to investigate how the perceptual features are encoded.
The model was able to synthesize drum sound components in such
detail that they could not be distinguished in an ABX test. This
method may therefore be capable of outperforming existing synthesis techniques, in terms of realism.
Sound examples available here.
Download Virtual Analog Modeling of Distortion Circuits Using Neural Ordinary Differential Equations Recent research in deep learning has shown that neural networks can learn differential equations governing dynamical systems. In this paper, we adapt this concept to Virtual Analog (VA) modeling to learn the ordinary differential equations (ODEs) governing the first-order and the second-order diode clipper. The proposed models achieve performance comparable to state-of-the-art recurrent neural networks (RNNs) albeit using fewer parameters. We show that this approach does not require oversampling and allows to increase the sampling rate after the training has completed, which results in increased accuracy. Using a sophisticated numerical solver allows to increase the accuracy at the cost of slower processing. ODEs learned this way do not require closed forms but are still physically interpretable.
Download RT-WDF — A Modular Wave Digital Filter Library with Support for Arbitrary Topologies and Multiple Nonlinearities Wave Digital Filters (WDF) [1] are a popular approach for virtual analog modeling [2]. They provide a computationally efficient way to simulate lumped physical systems with well-studied numerical properties. Recent work by Werner et al. [3, 4] enables the use of WDFs to model systems with complicated topologies and multiple/multiport nonlinearities, to a degree not previously known. We present an efficient, portable, modular, and open-source C++ library for real time Wave Digital Filter modeling: RT-WDF [5]. The library allows a WDF to be specified in an object-oriented tree with the same structure as a WDF tree and implements the most recent advances in the field. We give an architectural overview and introduce the main concepts of operation on three separate case studies: a switchable attenuator, the Bassman tone stack, and a common-cathode triode amplifier. It is further shown how to expand the existent set of non-linear models to encourage custom extensions. Index Terms— wave digital filter, software, real time, virtual analog modeling, multiple nonlinearities
Download Audio Processing Using Haskell The software for most today’s applications including signal processing applications is written in imperative languages. Imperative programs are fast because they are designed close to the architecture of the widespread computers, but they don’t match the structure of signal processing very well. In contrast to that, functional programming and especially lazy evaluation perfectly models many common operations on signals. Haskell is a statically typed, lazy functional programming language which allow for a very elegant and concise programming style. We want to sketch how to process signals, how to improve safety by the use of physical units, and how to compose music using this language.
Download An Algorithm for a Valved Brass Instrument Synthesis Environment using Finite-Difference Time-Domain Methods with Performance Optimisation This paper presents a physical modelling sound synthesis environment for the production of valved brass instrument sounds. The governing equations of the system are solved using finite-difference time-domain (FDTD) methods and the environment is implemented in the C programming language. Users of the environment can create their own custom instruments and are able to control player parameters such as lip frequency, mouth pressure and valve openings through the use of instrument and score files. The algorithm for sound synthesis is presented in detail along with a discussion of optimisation methods used to reduce run time. Binaries for the environment are available for download online for multiple platforms.
Download Delay Network Architectures for Room and Coupled Space Modeling Feedback delay network reverberators have decay filters associated with each delay line to model the frequency dependent reverberation time (T60) of a space. The decay filters are typically
designed such that all delay lines independently produce the same
T60 frequency response. However, in real rooms, there are multiple, concurrent T60 responses that depend on the geometry and
physical properties of the materials present in the rooms. In this
paper, we propose the Grouped Feedback Delay Network (GFDN),
where groups of delay lines share different target T60s. We use the
GFDN to simulate coupled rooms, where one room is significantly
larger than the other. We also simulate rooms with different materials, with unique decay filters associated with each delay line
group, designed to represent the T60 characteristics of a particular
material. The T60 filters are designed to emulate the materials’ absorption characteristics with minimal computation. We discuss the
design of the mixing matrix to control inter- and intra-group mixing, and show how the amount of mixing affects behavior of the
room modes. Finally, we discuss the inclusion of air absorption
filters on each delay line and physically motivated room resizing
techniques with the GFDN.