2:00 pm

N-1 A Single-Chip Three-Channel 112-dB Audio DAC with Audio DSP Capability

Robert Adams and Karl Sweetland, Analog Devices Inc., Acton, MA, USA

An audio DAC with internal DSP core has been designed that includes three high-quality audio DACs as well as a DSP programmed to provide algorithms that correct for speaker/amplifier deficiencies. These algorithms include equalization, two-band compression/limiting with arbitrary compression curve, spatial enhancement, delay and interpolation. All signal processing parameters are register-programmable using an external microcontroller. The DAC architecture uses a multi-bit sigma-delta design with a mismatch-shaping scrambler.

Convention Paper 5475

2:30 pm

N-2 Beyond CD Quality: Advanced Audio Coding (AAC) for High-Resolution Audio with 24-Bit Resolution and 96-kHz Sampling Frequency

Claus Bürgel, Reinfried Bartholomäus, Wolfgang Fiesel, Johannes Hilpert, Andreas Hölzer, Karsten Linzmeier and Martin Weishart, Fraunhofer Institute for Integrated Circuits, Erlangen, Germany

Contrary to the MPEG-1 Audio compression schemes, Advanced Audio Coding (AAC) in its MPEG-2 and MPEG-4 flavours has no inherent upper limit for the sampling frequency of the input signal. Furthermore, the bitstream format allows to cover a dynamic range far beyond the range provided by 24 bit linear PCM coding. This makes the AAC coder an ideal candidate for representing audio signals with parameters that are usually associated with high resolution audio systems. This paper discusses the application of this highly efficient compression scheme to digital programme material represented with 24 bit and 96 kHz.

Convention Paper 5476

3:00 pm

N-3 Towards a Better Understanding of 1-Bit Sigma-Delta Modulators - Part 2

Stanley P. Lipshitz and John Vanderkooy, University of Waterloo, Waterloo, Ontario, Canada

This paper extends our previous studies of 1-bit sigma-delta modulators. We now investigate 1l⁄2 bit (i.e., 3 level) systems, and again find that we can predict their idle-tone behavior and the spectral structure of their output. We address the question of whether sigma-delta modulators are adequately dithered by their internal noise, and compare the behavior of minimum-phase and nonminimum-phase (i.e., chaotic) modulator designs. Numerous computer simulations, greatly aided by coherent averaging, have guided us to two basic mechanisms that explain the distortion: the sweeping of the idle tone, and the saturating quantizer characteristic. A model of the nonlinearity of a dithered quantizer explains the general nature of the harmonic distortion components and their phases. The data also show unambiguously that the maximum possible dither should always be used.

Convention Paper 5477

3:30 pm

N-4 Effective Dither in High-Order Sigma-Delta Modulators

James A. S. Angus, University of Salford, Salford, Greater Manchester, UK

This paper clarifies some of the cofusion that has arisen over the efficacy of dither in PCM and Sigma-Delta modulation systems. It describes a fair means of comparison between them. It presents results that show dither is effective in sigma-delta modulation systems of any order and proposes methods for achieving optimum performance in both systems.

Convention Paper 5478

4:00 pm

N-5 Non-Invasive Identification of Audio Content for High-Resolution Applications

Malcolm O. J. Hawksford, University of Essex, Colchester, Essex, UK

A noninvasive method of audio file identification is described to ascertain the proximity of processed audio, of possibly dubious origin, to a reference file. A differential correction function forms the basis of a comparative metric. Testing embraces linear and nonlinear processes including perceptual-based codecs. Applications include DVD-A and SACD when used as the only legitimate nonwatermarked release formats.

Convention Paper 5479