Download Flutter Echo Modeling Flutter echo is a well-known acoustic phenomenon that occurs when sound waves bounce between two parallel reflective surfaces, creating a repetitive sound. In this work, we introduce a method to recreate flutter echo as an audio effect. The proposed algorithm is based on a feedback structure utilizing velvet noise that aims to synthesize the fluttery components of a reference room impulse response presenting flutter echo. Among these, the repetition time defines the length of the delay line in a feedback filter. The specific spectral properties of the flutter are obtained with a bandpass attenuation filter and a ripple filter, which enhances the harmonic behavior of the sound. Additional temporal shaping of a velvet-noise filter, which processes the output of the feedback loop, is performed based on the properties of the reference flutter. The comparison between synthetic and measured flutter echo impulse responses shows good agreement in terms of both the repetition time and reverberation time values.
Download Morphing Instrument Body Models In this study we present morphing methods for musical instrument body models using DSP techniques. These methods are able to transform a given body model gradually into another one in a controlled way, and they guarantee stability of the body models at each intermediate step. This enables to morph from a certain sized body model to a larger or smaller one. It is also possible to extrapolate beyond original models, thus creating new interesting (out of this world) instrument bodies. The opportunity to create a time-varying body, i.e., a model that changes in size over time, results in an interesting audio effect. This paper exhibits morphing mainly via guitar body examples, but naturally morphing can also be extended to other instruments with reverberant resonators as their bodies. Morphing from a guitar body model to a violin body model is viewed as an example. Implementation and perceptual issues of the signal processing methods are discussed. For related sound demonstrations, see www.acoustics.hut.fi/demo/ dafx2001-bodymorph/.
Download Extending Digital Waveguides To Include Material Modelling Digital Waveguides have been extensively used for musical instrument and room acoustics modelling. They can be used to form simplistic models for ideal wave propagation in one, two and three dimensions. Models in 1D for string and wind instrument synthesis and more recently a model for a drum, realised by interfacing 2D and 3D waveguide meshes, have been presented [1]. A framework is thus in place for the virtual construction of new or abstract musical instruments. However, straight-forward waveguides and waveguide meshes behave in an extremely indeal nature and phenomena such as stiffness and internal friction are often compromised or ignored altogether. In this paper we discuss and evaluate models which incorporate material parameters. We review a 1D bar model, and then present a 2D extension to model plates. We also discuss the problem of modelling frequency dependent damping, by describing a waveguide model of a visco-elastically damped string.
Download On Iterative Solutions for Numerical Collision Models Nonlinear interactions between different parts of musical instruments present several challenges regarding the formulation of reliable and efficient numerical sound synthesis models. This paper focuses on a numerical collision model that incorporates impact damping. The proposed energy-based approach involves an iterative solver for the solution of the nonlinear system equations. In order to ensure the efficiency of the presented algorithm a bound is derived for the maximum number of iterations required for convergence. Numerical results demonstrate energy conservation as well as convergence within a small number of iterations, which is usually much lower than the predicted bound. Finally, an application to music acoustics, involving a clarinet simulation, shows that including a loss mechanism during collisions may have a significant effect on sound production.
Download Digitizing the Ibanez Weeping Demon Wah Pedal Being able to transform an analog audio circuit into a digital model is a big deal for musicians, producers, and circuit benders alike. In this paper, we address some of the issues that arise when attempting to make such a digital model. Using the canonical state variable filter as the main point of interest in our schematic, we will walk through the process of making a signal flow graph, obtaining a transfer function, and making a usable digital filter. Additionally, we will address an issue that is common throughout virtual analog literature; reducing the very large expressions for each of the filter coefficients. Using a novel factoring algorithm, we show that these expressions can be reduced from thousands of operations down to tens of operations.
Download Dynamic Stochastic Wavetable Synthesis Dynamic Stochastic Synthesis (DSS) is a direct digital synthesis method invented by composer Iannis Xenakis and notably employed in his 1991 composition GENDY3. In its original conception, DSS generates periodic waves by linear interpolation between a set of breakpoints in amplitude–time space. The breakpoints change position each period, displaced by random walks via high-level parameters that induce various behaviors and timbres along the pitch–noise continuum. The following paper proposes Dynamic Stochastic Wavetable Synthesis as a modification and generalization of DSS that enables its application to table-lookup oscillators, allowing arbitrary sample data to become the basis of a DSS process. We describe the considerations affecting the development of such an algorithm and offer a real-time implementation informed by the analysis.
Download FAUST Architectures Design and OSC Support FAUST [Functional Audio Stream] is a functional programming language specifically designed for real-time signal processing and synthesis. It consists in a compiler that translates a FAUST program into an equivalent C++ program, taking care of generating the most efficient code. The FAUST environment also includes various architecture files, providing the glue between the FAUST C++ output and the host audio and GUI environments. The combination of architecture files and FAUST output gives ready to run applications or plugins for various systems, which makes a single FAUST specification available on different platforms and environments without additional cost. This article presents the overall design of the architecture files and gives more details on the recent OSC architecture.
Download Doppler Simulation and the Leslie An efficient algorithm for simulating the Doppler effect using interpolating and de-interpolating delay lines is described. The Doppler simulator is used to simulate a rotating horn to achieve the Leslie effect. Measurements of a horn from a real Leslie are used to calibrate angle-dependent digital filters which simulate the changing, angle-dependent, frequency response of the rotating horn.
Download Spatial High Frequency Extrapolation Method for Room Acoustic Auralization Auralization of numerically modeled impulse responses can be informative when assessing the geometric characteristics of a room. Wave-based acoustic modeling methods are suitable for approximating low frequency wave propagation. Subsequent auralizations are perceived unnaturally due to the limited bandwidth involved. The paper presents a post-processing framework for extending low-mid frequency band limited spatial room impulse responses (SRIR) to include higher frequency signal components without the use of geometric modeling methods. Acoustic parameters for extrapolated RIRs are compared with reference measurement data for existing venues and a Finite Difference Time Domain modeled SRIR is extrapolated to produce a natural sounding full-band SRIR signal. The method shows promising agreement particularly for large venues as the air absorption is more dominant than the boundary absorption at high frequencies.
Download Distortion and Pitch Processing Using a Modal Reverberator Architecture A reverberator based on a room response modal analysis is adapted to produce distortion, pitch and time manipulation effects, as well as gated and iterated reverberation. The so-called “modal reverberator” is a parallel collection of resonant filters, with resonance frequencies and dampings tuned to the modal frequencies and decay times of the space or object being simulated. Here, the resonant filters are implemented as cascades of heterodyning, smoothing, and modulation steps, forming a type of analysis/synthesis architecture. By applying memoryless nonlinearities to the modulating sinusoids, distortion effects are produced, including distortion without intermodulation products. By using different frequencies for the heterodyning and associated modulation operations, pitch manipulation effects are generated, including pitch shifting and spectral “inversion.” By resampling the smoothing filter output, the signal time axis is stretched without introducing pitch changes. As these effects are integrated into a reverberator architecture, reverberation controls such as decay time can be used produce novel effects having some of the sonic characteristics of reverberation.