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Jun. 2, 2008 Student: Shang-Yu Yeh ( 葉尚諭 ) Advisor: Dr. Hsueh -Ming Hang ( 杭學鳴 )

Coding Efficiency and Quality Improvement for MPEG Surround Encoding. Jun. 2, 2008 Student: Shang-Yu Yeh ( 葉尚諭 ) Advisor: Dr. Hsueh -Ming Hang ( 杭學鳴 ). My Work. Design MPEG Surround Encoding Algorithms Subset coding mode Parameter band stride Parameter set

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Jun. 2, 2008 Student: Shang-Yu Yeh ( 葉尚諭 ) Advisor: Dr. Hsueh -Ming Hang ( 杭學鳴 )

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  1. Coding Efficiency and Quality Improvement for MPEG Surround Encoding Jun. 2, 2008 Student: Shang-Yu Yeh (葉尚諭) Advisor: Dr. Hsueh-Ming Hang (杭學鳴)

  2. My Work • Design MPEG Surround Encoding Algorithms • Subset coding mode • Parameter band stride • Parameter set • Adaptive parameter smoothing • Implementation and Simulation on the Reference Software

  3. Outline • MPEG Surround Introduction • Proposed Modules and Experimental Results • Conclusions and Future Work • Demo

  4. Outline • MPEG Surround Introduction • Spatial Hearing • MPEG Surround Encoder • MPEG Surround Decoder • Proposed Modules and Experimental Results • Conclusions and Future Work • Demo

  5. Spatial Hearing • Describing how human locate sound source in the horizontal place • Interaural Level Difference (ILD) • Interaural Time Difference (ITD) • Interaural Coherence (IC)

  6. MPEG Surround • Low-bitrate parametric coding technology for multi-channel audio signals • Backward compatibility to the conventional stereo system • Standardization • CfP on SAC in March 2004 • Finalize in July, 2006 (ISO/IEC 23003-1)

  7. MPEG Surround Encoder • Capture the spatial image of multi-channel audio • Generate a mono/stereo downmix

  8. MPEG Surround Decoder • Synthesize multi-channel output signal • Backward compatibility

  9. Downmix and Parameter Extraction • Two elementary blocks construct hierarchical structures • R-OTT box (Reverse One-To-Two box) • R-TTT box (Reverse Two-To-Three box)

  10. Parameter Sets and Bands • Parameter sets: grouping of time slots • Parameter bands: grouping of subbands

  11. R-OTT Box • Create a mono downmix from a stereo input • Extract relevant spatial parameters • Channel Level Differences (CLD) where • Inter-Channel coherence (ICC)

  12. R-TTT Box • Create a stereo downmix from three input channels • Two way to reconstruction the 3rd signal • Prediction mode: 2 CPCs and ICC • Energy mode: 2CLDs

  13. Quantization and Entropy Coding Schemes • Quantization - fine and coarse • Entropy coding - Differential coding + Huffman tables

  14. Outline • MPEG Surround Introduction • Proposed Modules and Experimental Results • Subset coding mode • Parameter band stride • Parameter set • Adaptive parameter smoothing • Conclusions and Future Work • Demo

  15. New Encoder Structure • 4 Additional modules:

  16. Subset Coding Mode • 4 coding modes for each parameter subset: • Default(0) • Keep(1) • Interpolation(2) • Lossless(3) • Ref S/W implements only the Lossless mode

  17. Subset Coding Mode • Flow chart: • Search each mode for the least error • Compare the error with a threshold • Exploit correlation of time

  18. Experimental Results • Only the Lossless mode costs bits • The bitrate reduction can be estimated:

  19. Experimental Results • 2 observations: • Theoretical results larger than experimental results • Differential coding schemes • Number of parameter sets increases => theoretical & experimental results decrease • Probability distributions

  20. Experimental Results • Distributions of DT data:

  21. Parameter Band Stride • Parameter band cannot be adjusted • The frequency resolution is adjusted by “parameter band stride” • 4 strides for each parameter subset

  22. Parameter Band Decision • Combined with the pairing decision • Flow chart : • 2 successive lossless subsets • 1 single subset • Exploit correlation of frequency

  23. Parameter Band Decision • 4 possible results: • 2 successive subsets in a pair with the same stride (>1) • 2 successive subsets using different strides (>1) • 2 successive subsets in a pair with stride=1 • 1 subset coded individually

  24. Experimental Results • The bitrate can be estimated by :

  25. Experimental Results • 2 observations: • Theoretical results larger than experimental results • Differential coding schemes • Number of parameter sets increases => theoretical & experimental results decrease • Probability distributions

  26. Experimental Results • Distributions of DF data

  27. Comparisons of Previous 2 Modules • Using coding mode is more efficient than pbstride • Compare the DT and DF data

  28. Comparisons of Previous 2 Modules • Using pbstride are more overestimated than using coding mode modules • Differential coding schemes

  29. Experimental Results-Combined with Coding Mode • Bitrate reduction percentage: 25~55% • Complexity: 0.13%

  30. Parameter set • Describing the number of parameters for each parameter band • 2 kinds of framing: • Fixed framing: divided into equal parts • Variable framing: arbitrary divisions • 1~8 parameter sets • Requiring dynamic decision

  31. Time Resolution • A border assigned • Large difference between nearby parameters • Calculate the differences of backward and forward extractions • Set time borders at time slots with larger differences

  32. Time Resolution Decision • Flow chart:

  33. Experimental Results • waveforms • (a) original signal • (b) decoded signal using ps=1 • (c) decoded signal using adaptive decision

  34. Experimental Results • Additional bitrate: • Complexity:

  35. Parameter Smoothing • Compensate for artifacts caused by coarse quantization • Performed at the decoder side • 1st order IIR filter

  36. Parameter Smoothing • Flow chart: • Compare coarse-quantized and smoothed parameters with fine quantized parameters • Choose the configure with the least error

  37. Experimental Results • Quantization error:

  38. Experimental Results • waveforms • (a) fine quantized • (b) coarse quantized • (c) coarse quantized and smoothed

  39. Experimental Results • Bitrate variations: • Complexity:

  40. Outline • MPEG Surround Introduction • Proposed Modules and Experimental Results • Conclusions and Future Work • Demo

  41. Conclusions • Design and implementation of four encoding modules in MPEG Surround encoder • Exploit correlation along time axis and frequency axis • Bitrate reduction: 25~55% • Theoretical Estimation • Adaptive time resolution and parameter smoothing

  42. Future Work • Modify error measures • Different band weights • Different parameter weights • Find a more precise evaluation of quality for fine-tuning • Some other tools • Residual coding, temporal shaping…etc

  43. Outline • MPEG Surround Introduction • Proposed Modules and Experimental Results • Conclusions and Future Work • Demo

  44. Demo

  45. Appendix

  46. Experimental Results • waveforms

  47. Filter Banks • 2 stages

  48. OTT Box • Synthesize by a mono downmix with parameters

  49. R-TTT Box(2/2) • Prediction mode: • 2 CPCs and 1 ICC: where • Energy Mode: • 2 CLDs:

  50. TTT Box • Prediction Mode: • With residual signal-> 2 CPCs • Without residual signal-> use the ICC to compensate the energy loss • Energy Mode: • Energy reconstruction

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