2:00 pm

M-1 A Tutorial on Performance Metrics and Noise Propagation in Digital IIR Filters

Duane K. Wise, Consultant, Boulder, CO, USA (Invited)

This paper addresses issues of digital IIR filter performance, namely the likelihood of fixed-point overflow and the propagation of quantization error. Measuring these quantities requires a method of determining a transfer function between arbitrary nodes of a filter structure. Norm functions are defined for application to these transfer functions which address overflow and error propagation issues depending on the signals employed. In addition, functions of the state matrix of an IIR filter are defined that measure the potential for limit cycles.

Convention Paper 5470

2:30 pm

M-2 Audio Coding Based on Integer Transforms

Ralf Geiger, Thomas Sporer and Jürgen Koller, Fraunhofer Institute for Integrated Circuits, Ilmenau, Germany
Karlheinz Brandenburg, Fraunhofer Institute for Integrated Circuits, Ilmenau and Ilmenau Technical University, Ilmenau, Germany

Most of the current audio coding schemes use transforms like the Modified Discrete Cosine Transform (MDCT) to calculate a blockwise frequency representation of the audio signal. Since these transforms usually produce floating point values even for integer input samples, a quantization process is necessary to achieve a reduction of data rate. This paper presents a new transform with perfect reconstruction that produces integer output values. The transform is called IntMDCT and is derived from the MDCT preserving most of its attractive properties. It provides a good spectral representation of the audio signal, critical sampling and overlapping of blocks. A lossless audio coding scheme may be built by simply cascading IntMDCT with an entropy coding scheme.

Convention Paper 5471

3:00 pm

M-3 Efficient Compression of Oversampled 1-Bit Audio Signals

Joshua D. Reiss and Mark B. Sandler, King's College, Strand, London, UK

Sigma delta modulation is a popular technique for high-resolution analog-to-digital conversion and digital-to-analog-conversion. It has been considered as a new format for recording and storage of audio signals. To reduce the storage capacity, a lossless compression scheme can be applied. However, this scheme offers less than 3:1 compression. This may not be sufficient for storage on media such as a Digital Versatile Disk (DVD). We propose a scheme based on a technique known as bit-grouping. Errors are introduced in the compression, but they are confined to frequencies outside the audible range. Our studies indicate that bit-grouping allows one to achieve greater than 4:1 compression.

Convention Paper 5472

3:30 pm

M-4 Audio Applications of the Teager Energy Operator

Mark Kahrs, Helsinki University of Technology, Espoo, Finland

The Teager Energy Operator (TEO) is a nonlinear time domain operator with a delightfully simple implementation. We first review the TEO as well as the Discrete Energy Separation Algorithm (DESA). We compare Short Time Fourier Transform techniques such as the well known Phase Vocoder with the Energy Separation operator using synthetic signals. We also study the performance with noise. We also compare the Hilbert Transform Instantaneous Frequency detection with the TEO. We review the use of the DESA operator in musical instrument analysis and discuss the use of the TEO in transient detection.

Convention Paper 5473

4:00 pm

M-5 IIR Biquad Controllers for Low-Frequency Acoustic Resonance

Mark R. Avis, University of Salford, Salford, Greater Manchester, UK

Low frequency normal modes of an enclosed soundfield introduce unwanted frequency, spatial and temporal artefacts to reproduced electroacoustic signals. A novel control approach is presented based on an analytical modal decomposition, which incorporates a low-frequency soundfield model formed from the sum of a number of second-order IIR filter sections. It is shown that within constraints determined by the model accuracy, IIR controllers may be constructed and may be applied to control tasks such as point pressure cancellation and the reduction of modal quality factor.

Convention Paper 5474

4:30 pm

M-6 Low-Frequency Control in Small- to Medium-Sized Listening Environments

Dirk Noy, WSDG-E, Liestal, Switzerland
John Storyk, WSDG, Highland, NY, USA

The advent of surround sound production and reproduction environments has highly increased the importance of low frequency control. On one hand this is due to the addition of a dedicated low frequency loudspeaker ('Subwoofer' or LFE) - on the other hand the increased number of sources (Center Channel and Surround Loudspeakers) is causing more complex interference patterns. The paper presents a summary of basic room acoustics low frequency parameters such as eigentones and pressure zones. The authors will furthermore explore recent design, installation and testing for three small critical listening environments, specifically with respect to low frequency response. Conclusions and continued questions for the professional audio industry will be summarized.

No Convention Paper Printed