AE-5.1

Reduction of the Dispersion Error in the Interpolated Digital Waveguide Mesh Using Frequency Warping
Lauri Savioja, Vesa Valimaki (Helsinki University of Technology, Laboratory of Acoustics and Audio Signal Processing)

The digital waveguide mesh is an extension of the one-dimensional digital waveguide technique. The mesh is used for simulation of two- and three-dimensional wave propagation in musical instruments and acoustic spaces. The rectangular digital waveguide mesh algorithm suffers from direction-dependent dispersion. By using the interpolated mesh, nearly uniform wave propagation characteristics are obtained in all directions. In this paper we show how the dispersion error of the interpolated mesh can be reduced by frequency warping. By using this technique the bandwidth where the frequency accuracy is within 1% tolerance is more than doubled.

AE-5.2

Plucked-String Synthesis Algorithms with Tension Modulation Nonlinearity
Vesa Valimaki, Tero Tolonen, Matti Karjalainen (Helsinki University of Technology, Laboratory of Acoustics and Audio Signal Processing)

Digital waveguide modeling of a nonlinear vibrating string is investigated when the nonlinearity is essentially caused by ten-sion modulation. We derive synthesis models where the nonlinearity is implemented with a time-varying fractional delay filter. Also, conversion from a dual-delay-line physical model into a single-delay-loop model is explained. Realistic synthetic tones with nonlinear effects are obtained by introducing minor amendments to a linear string synthesis algorithm. It is shown how synthetic plucked-string tones are modified as a consequence of tension modulation. Examples of synthesized tones are available at http://www.acoustics.hut.fi/~ttolonen/sounddemos/tmstr/.

AE-5.3

Sinusoidal Modeling Using Frame-based Perceptually Weighted Matching Pursuits
Tony S Verma, Teresa H.Y. Meng (Stanford University)

We propose a method for sinusoidal modeling that takes into account the psychoacoustics of human hearing using a frame-based perceptually weighted matching pursuit. Working on blocks of the input signal, a set of sinusoidal components for each block is iteratively extracted taking into consideration perceptual significance by using extensions to the well known matching pursuits algorithm. These extensions allow including information about the time-varying masking threshold of the input signal during the pursuit. The blocks overlap-add together to reconstruct the entire signal. Although the perceptually weighted matching pursuit on each block can iterate until the error between the original and the reconstructed signal is zero, lower order approximations are possible by stopping the pursuit when the error becomes imperceptible to the human ear or by stopping the pursuit after a number of the perceptually most significant sinusoidal elements are found. The proposed sinusoidal model finds use in many applications including signal modifications and compression.

AE-5.4

A Switched Parametric & Transform Audio Coder
Scott N Levine, Julius O Smith III (Stanford University)

In this paper, we present a system of sines+transients+noise modeling techniques that dynamically switches between parametric representations and transform coding based representations. The sines and noise are represented by parametric models using multiresolution sinusoidal modeling and Bark-band noise modeling, respectively. The transients are modeled by short regions of transform coding. In addition, new methods are presented for selection and quantization of sinusoidal trajectories based on trajectory length and signal-to-masking thresholds. This system is useful for both low bitrate audio coding (20-40 kbps) and compressed-domain processing, such as time-scale modification.

AE-5.5

Perception-based Residual Analysis-synthesis System
Yin H Lam, Robert W Stewart (University of Strathclyde)

The paper describes a residual analysis-synthesis system which exploits the human perception mechanism on temporal varying signals using Zwicker's three dimensional excitation-critical-band-rate time pattern as the framework. Temporal information is retrieved using a linear predictive analysis on the discrete cosine transformed signal and critical band intensity information is obtained by using non-uniform filter banks. The system is characterized by high frequency resolution and good time resolution. Novel phase prediction and phase correction techniques are employed to eliminate any boundary discontinuities between two time frames. Experimental results illustrate that high quality residual signals can be reproduced using a few parameters regardless of the temporal characteristics of the signal.

AE-5.6

A Fixed-point Recursive Digital Oscillator for Additive Synthesis of Audio
Todd D Hodes, John Hauser, Adrian Freed, John Wawrzynek, David Wessel (University of California, Berkeley)

This paper summarizes our work adapting a recursive digital resonator for use on sixteen-bit fixed-point hardware. Our modified oscillator is a two-pole filter that maintains frequency precision at a cost of two additional operations per filter sample. The new filter's error properties are expressly matched to use in the range of frequencies relevant to additive synthesis of digital audio and sinusoidal modelling of speech in order to minimize the additional computational overhead. We present the algorithm, an error analysis, a performance analysis, and measurements of an implementation on a fixed-point vector microprocessor system.

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Last Update: February 4, 1999 Ingo Höntsch