Download Towards Inverse Virtual Analog Modeling Several digital signal processing approaches, generally referred to as Virtual Analog (VA) modeling, are currently under development for the software emulation of analog audio circuitry. The main purpose of VA modeling is to faithfully reproduce the behavior of real-world audio gear, e.g., distortion effects, synthesizers or amplifiers, using efficient algorithms. In this paper, however, we provide a preliminary discussion about how VA modeling can be exploited to infer the input signal of an analog audio system, given the output signal and the parameters of the circuit. In particular, we show how an inversion theorem known in circuit theory, and based on nullors, can be used for this purpose. As recent advances in Wave Digital Filter (WDF) theory allow us to implement circuits with nullors in a systematic fashion, WDFs prove to be useful tools for inverse VA modeling. WDF realizations of a nonlinear audio system and its inverse are presented as an example of application.
Download Sound Processing in OpenMusic This article introduces some new possibilities of audio manipulations and sound processing in the Computer-Aided Composition environment OpenMusic. Interfaces with underlying sound processing systems are described, with an emphasis on the use of the symbolic and visual programming environment for the design of sound computation processes.
Download Do You Hear a Bump or a Hole? An Experiment on Temporal Aspects in Footsteps Recognition In this paper, we present a preliminary experiment whose goal is to assess the role of temporal aspects in sonically simulating the act of walking on a bump or a hole. In particular, we investigate whether the timing between heel and toe and the timing between footsteps affects the perception of walking on unflat surfaces. Results show that it is possible to simulate a bump or a hole by only using temporal information in the auditory modality.
Download Application of non-negative matrix factorization to signal-adaptive audio effects This paper proposes novel audio effects based on manipulating an audio signal in a representation domain provided by non-negative matrix factorization (NMF). Critical-band magnitude spectrograms Y of sounds are first factorized into a product of two lower-rank matrices so that Y ≈ BG. The parameter matrices B and G are then processed in order to achieve the desired effect. Three classes of effects were investigated: 1) dynamic range compression (or expansion) of the component spectra or gains, 2) effects based on rank-ordering the components (colums of B and the corresponding rows of G) according to acoustic features extracted from them, and then weighting each component according to its rank, and 3) distortion effects based on controlling the amount of components (and thus the reconstruction error) in the above linear approximation. The subjective quality of the effects was assessed in a listening test.
Download Audio Rendering System Design for an Object Oriented Audio Visual Human Perception Assessment Tool The cognitive processes behind human bimodal (audio visual) perception are not well understood. This contribution presents an approach to reach a deeper understanding by means of subjective assessments of (interactive) audio visual applications. A tool developed for performing these assessments is introduced, and the audio rendering system design of that tool is explained: its modular character, the signal processing flow as well as the possible reproduction setups are discussed. Finally, an example for the assessment of geometrically based room simulation and preliminary test results are given.
Download Perceptual Linear Filters: Low-Order ARMA Approximation for Sound Synthesis This paper deals with the approximation of a given frequency response by a low-order linear ARMA filter (Auto-Regressive Moving Average). The aim of this work is the audio synthesis, then to improve the perceptual quality, a criterion based on human listening is defined and minimized. Two complementary approaches are proposed here for solving this non-linear and non-convex problem: first, a weighted version of the Iterative Prefiltering, second, an adaptation of the Gauss-Newton method. This algorithm is adapted to guarantee the causality/stability of the obtained filter, and eventually its minimum phase property. The benefit of the new method is illustrated and evaluated.
Download DHM and FDTD based Hardware Sound Field Simulation Acceleration Sound field simulation is widely used for acoustic design; however, this simulation needs many computational resources. On the other hand, FPGA becomes major for acceleration. To take advantage of hardware acceleration by FPGA, hardware oriented algorithm which consumes small number of gates and memory is necessary. This paper addresses hardware acceleration of sound field simulation using FPGA. Improved Digital Huygens Model (DHM) for hardware is implemented and speed up ratio is examined. For 2D simulation, the implemented accelerator is 1,170 times faster than software simulation. For 3D simulation, it is shown that FDTD based method is suitable for hardware implementation and required hardware resource are estimated.
Download Compositional Sketches in PWGLSynth PWGLSynth has already a long history in controlling physicsbased instruments. The control system has been score-based, i.e. the user prepares a score in advance, and by interactive listening process the result can be be refined either by adjusting score information, performance rules and/or the visual instrument definition. This scheme allows detailed control on how the instrument model reacts to control information generated from the score. This paper presents a complementary approach to sound synthesis where the idea is to generate algorithmically typically relatively short musical textures. The user can improvise with various compositional ideas, adjust parameters, and listen to the results in real-time either individually or interleaved. This is achieved by utilizing a special code-box scheme that allows any textual Lisp expression to be interfaced to the visual part of the PWGL system.
Download Coefficient-modulated first-order allpass filter as distortion effect A novel approach to implement the distortion effect is introduced. The proposed approach is based on time-varying phase distortion of the input signal, and it is implemented using a coefficient modulated first-order allpass filter. This new technique provides control over the distorted band with a proper choice of the modulating signal. By choosing a modulating signal that applies the phase distortion only for low frequencies, the aliasing often generated by conventional distortion effects, which modify the signal amplitude, can be greatly reduced. Modulation signals that produce distortion effects applicable for electric guitar playing are also discussed. Sound examples on the use of the filter can be found at http://www.acoustics.hut.fi/~jpekonen/ Papers/dafx08/.
Download Musikverb: A Harmonically Adaptive Audio Reverberation We present MusikVerb, a novel digital reverberation capable of adapting its output to the harmonic context of a live music performance. The proposed reverberation is aware of the harmonic content of an audio input signal and ‘tunes’ the reverberation output to its harmonic content using a spectral filtering technique. The dynamic behavior of MusikVerb avoids the sonic clutter of traditional reverberation, and most importantly, fosters creative endeavor by providing new expressive and musically-aware uses of reverberation. Despite its applicability to any input audio signal, the proposed effect has been designed primarily as a guitar pedal effect and a standalone software application.