High resolution analog-to-digital conversion and digital-to-analog conversion is often realized with the use of a Sigma-Delta Modulator (SDM). The sigma-delta modulation process, although very non-linear when a 1-bit quantizer is used, is nowadays well understood and can be made to deliver a very high signal conversion quality. An example system that pushes the traditional sigma-delta modulation algorithm to its performance limit is the Super Audio CD (SA-CD) standard, in which a 64 times oversampled 1-bit signal is used to represent audio content with an SNR of up to 120~dB over 20~kHz bandwidth.
Look-Ahead Based Sigma-Delta Modulation presents a number of alternative digital sigma-delta modulation techniques that make use of look-ahead, a process that takes into account the effect of decisions on the future, to realize an even higher conversion quality than possible with traditional sigma-delta modulation.
This book provides the reader with a clear overview of various encoding techniques and demonstrates the improvements in signal conversion quality that can be obtained from their use. Starting from the basic full look-ahead approach that requires several orders of magnitude more computational power than a normal SDM, more efficient structures are derived that are able to realize a far higher signal conversion performance at a fraction of the computational cost. In addition to this, a modulator is derived that is able to generate bitstreams that are optimized for SA-CD usage, i.e. a high signal conversion quality combined with minimal signal entropy.
All the look-ahead algorithms presented in this book are described in pseudocode and ample simulation results are provided to judge the effects on the signal conversion performance.
Zusammenfassung
The aim of this book is to expand and improve upon the existing knowledge on discrete-time 1-bit look-ahead sigma-delta modulation in general, and to come to a solution for the above mentioned specific issues arising from 1-bit sigma-delta modulation for SA-CD. In order to achieve this objective an analysis is made of the possibilities for improving the performance of digital noise-shaping look-ahead solutions. On the basis of the insights obtained from the analysis, several novel generic 1-bit look-ahead solutions that improve upon the state-of-the-art will be derived and their performance will be evaluated and compared. Finally, all the insights are combined with the knowledge of the SA-CD lossless data compression algorithm to come to a specifically for SA-CD optimized look-ahead design.
Inhalt
1. Introduction.- 2. Basics of sigma-delta modulation.- 3. Transient SDM performance.- 4. Noise-shaping quantizer model.- 5. Look-ahead sigma-delta modulation.- 6. Reducing the complexity of LA DD conversion.- 7. Trellis sigma-delta modulation.- 8. Efficient Trellis sigma-delta modulation.- 9. Pruned Tree sigma-delta modulation.- 10. Pruned Tree sigma-delta modulation for SA-CD.- 11. Comparison of look-ahead SDM techniques.- 12. Maximum SNR analysis.- 13. General Conclusions.- Appendix A: FFT calculations - coherent and power averaging.- Appendix B: Descriptions of the used Sigma-Delta Modulators.