Download Simplified, Physically-Informed Models of Distortion and Overdrive Guitar Effects Pedals This paper explores a computationally efficient, physically informed approach to design algorithms for emulating guitar distortion circuits. Two iconic effects pedals are studied: the “Distortion” pedal and the “Tube Screamer” or “Overdrive” pedal. The primary distortion mechanism in both pedals is a diode clipper with an embedded low-pass filter, and is shown to follow a nonlinear ordinary differential equation whose solution is computationally expensive for real-time use. In the proposed method, a simplified model, comprising the cascade of a conditioning filter, memoryless nonlinearity and equalization filter, is chosen for its computationally efficient, numerically robust properties. Often, the design of distortion algorithms involves tuning the parameters of this filter-distortion-filter model by ear to match the sound of a prototype circuit. Here, the filter transfer functions and memoryless nonlinearities are derived by analysis of the prototype circuit. Comparisons of the resulting algorithms to actual pedals show good agreement and demonstrate that the efficient algorithms presented reproduce the general character of the modeled pedals.
Download Adjustable Boundary Conditions for Multidimensional Transfer Function Models Block based physical modeling requires to provide a library of modeling blocks for standard components of real or virtual musical instruments. Complex synthesis models are built by connecting standard components in a physically meaningful way. These connections are investigated for modeling a resonating structure as a distributed parameter system. The dependence of a resonator’s spectral structure on the termination of its ports is analyzed. It is shown that the boundary conditions of a distributed parameter system can be adjusted by proper termination only. Examples show the corresponding variation of the resonator’s spectral structure in response to variations of the external termination.
Download Self-Sustained Vibrating Structures Physical Modelling by Means of Mass-Interaction Networks GENESIS is a sound synthesis and musical creation environment based on the mass-interaction CORDIS-ANIMA physical modelling formalism. It has got the noteworthy property that it allows to work both on sound itself and on musical composition in a single coherent environment. In this paper we present the first results of a study that is carried out with GENESIS on a particular type of models: self-sustained oscillating structures. By trying to build physical models of real instruments like bowed strings or woodwinds, our aim is to develop and analyse generic tools that can be used for the production of self-sustained oscillations on every mass-interaction network built with GENESIS. But, if the family of the self-sustained oscillating structures is very interesting to create rich timbres, it can also play a new and fundamental role at the level of the temporal macrostructure of the music (that of the gesture and the instrumental performance, as well as the composition). Indeed, it is possible, as we will propose in this paper, to use the relatively complex motion of a bowed macrostructure in a musical composition way, as a musical events generator.
Download Filtering within the Framework of Mass-Interaction Physical Modeling and of Haptic Gestural Interaction A variety of filters have been designed, synthesized and used in the history of electronic and computer music. All the approaches aimed to provide filters fulfilling several specifications such as frequency response, phase response, transient state characteristics like rise time and overshoot, realizably conditions concerning the technology used for the implementation and even economical considerations. One of the most important aspects concerning the filters dedicated to musical applications is the control structure they provide to the musician, who is in charge for the integration of the filtering operation in the compositional process and performance. Designing filters using the mass interaction scheme embedded in the CORDIS-ANIMA formalism (used for sound synthesis and composition by physical modelling) offers a different methodology in the control which is coherent with the philosophy of musical composition by ‘physical thinking’. This article introduces a technique to design filters using the CORDIS-ANIMA simulation language.
Download Real-Time Reverb Simulation Using Arbitrary Models We present a method for simulating reverberation in real-time using arbitrary object shapes. This method is an extension of digital plate reverberation where a dry signal is filtered through a physical model of an object vibrating in response to audio input. Using the modal synthesis method, we can simulate the vibration of many different shapes and materials in real time. Sound samples are available at the follwing website: http://cynthia.code404.com/dafx-audio/.
Download Hyper-Dimensional Digital Waveguide Mesh for Reverberation Modeling Characteristics of digital waveguide meshes with more than three physical dimensions are studied. Especially, the properties of a 4-D mesh are analyzed and compared to waveguide structures of lower dimensionalities. The hypermesh produces a response with a dense and irregular modal pattern at high frequencies, which is beneficial in modeling the reverberation of rooms or musical instrument bodies. In addition, it offers a high degree of decorrelation between output points selected at different locations, which is advantageous for multi-channel reverberation. The frequencydependent decay of the hypermesh response can be controlled using boundary filters introduced recently by one of the authors. Several hypermeshes can be effectively combined in a multirate system, in which each mesh produces reverberation on a finite frequency band. The paper presents two hypermesh application examples: the modeling of the impulse response of a lecture hall and the simulation of the response of a clavichord soundbox.
Download Ray Acoustics Using Computer Graphics Technology The modeling of room acoustics and simulation of sound wave propagation remain a difficult and computationally expensive task. Two main techniques have evolved, with one focusing on a real physical - wave-oriented - sound propagation, while the other approximates sound waves as rays using raytracing techniques. Due to many advances in computer science, and especially computer graphics over the last decade, interactive 3D sound simulations for complex and dynamic environments are within reach. In this paper we analyze sound propagation in terms of acoustic energy and explore the possibilities to map these concepts to radiometry and graphics rendering equations. Although we concentrate on ray-based techniques, we also partially consider wavebased sound propagation effects. The implemented system exploits modern graphics hardware and rendering techniques and is able to efficiently simulate 3D room acoustics, as well as to measure simplified personal HRTFs through acoustic raytracing.
Download Real-Time and Efficient Algorithms for Frequency Warping Based on Local Approximations of Warping Operators Frequency warping is a modifier that acts on sound signals by remapping the frequency axis. Thus, the spectral content of the original sound is displaced to other frequencies. At the same time, the phase relationship among the signal components is altered, nonlinearly with respect to frequency. While this effect is interesting and has several applications, including in the synthesis by physical models, its use has been so far limited by the lack of an accurate and flexible real-time algorithm. In this paper we present methods for frequency warping that are based on local approximations of the warping operators and allow for real-time implementation. Filter bank structures are derived that allow for efficient realization of the approximate technique. An analysis of the error is also presented, which shows that both numerical and perceptual errors are within acceptable limits. Furthermore, the approximate implementation allows for a larger variety of warping maps than that achieved by the classical (non-causal) first-order allpass cascade implementation.
Download The Origins of DAFx and its Future within the Sound and Music Computing Field DAFX is an established conference that has become a reference gathering for the researchers working on audio signal processing. In this presentation I will go back ten years to the beginning of this conference and to the ideas that promoted it. Then I will jump to the present, to the current context of our research field, different from the one ten years ago, and I will make some personal reflections on the current situation and the challenges that we are encountering.
Download 2nd Order Spherical Harmonic Spatial Encoding of Digital Waveguide Mesh Room Acoustic Models The aim of this research is to provide a solution for listening to the acoustics of Digital Waveguide Mesh (DWM) modelled virtual acoustic spaces. The DWM is a numerical simulation technique that has shown to be appropriate for modelling the propogation of sound through air. Recent work has explored methods for spatially capturing a soundfield within a virtual acoustic space using spatially distributed receivers based on sound intensity probe theory. This technique is now extended to facilitate spatial encoding using second-order spherical harmonics. This is achieved through an array of pressure sensitive receivers arranged around a central reference point, with appropriate processing applied to obtain the second-order harmonic signals associated with Ambisonic encoding/decoding. The processed signals are tested using novel techniques in order to objectively assess their integrity for reproducing a faithful impression of the virtual soundfield over a multi-channel sound system.