Book on DAFX - Digital Audio Effects Edited by Udo Zölzer ISBN: 0-471-49078-4 John Wiley & Sons, 2002

Chapter 13

M. Sandler and U. Zölzer

The motivation for Bitstream Signal Processing (BSP) Sigma Delta Modulation (SDM) has become the predominant means for converting between analog and digital domains for audio. There are various reasons for this, principal among them initially at least, was the low cost of SDM Digital-to-analog Converters (DACs) providing a quality equivalent to Nyquist-rate DACs. There are also good sonic arguments for the use of SDM data converters, currently mirrored in the debate of 96 kHz and 192 kHz sampling rates, which is that the benign and slow rate of roll-off of the anti-aliasing filters does not compromise the phase response. Thus a question arises. Would it not be simpler (not to mention more elegant) if we could perform the processing directly on the SDM bitstream that comes out of the SDM ADC, and write it directly to the SDM DAC? This chapter illustrates new challenges of bitstream signal representations, shows the fundamental basics and introduces filtering concepts for bitstream signal processing.

Contents

• Introduction
• Sigma Delta Modulation
  • A simple linearized model of SDM
  • A first order SDM system
  • Second and higher order SDM systems
• BSP Filtering Concepts
  • Addition and multiplication of bitstream signals
  • SD IIR Filters
  • SD FIR Filters
• Conclusion
• Bibliography

Keywords: Signal Representations, Sigma Delta Modulation, Bitstream Representation, Bitstream Signal Processing

Contents