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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 sets Adaptive smoothing

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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 sets • Adaptive smoothing • Implementation in the Reference Software

  3. Outline • MPEG Surround Introduction • Proposed Procedures and Experimental Results • Conclusion and Future Work • Demo

  4. Outline • MPEG Surround Introduction • Spatial Hearing • MPEG Surround Encoder • MPEG Surround Decoder • Proposed Procedures and Experimental Results • Conclusion 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 signal • Backward compatibility to stereo equipment • 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 • Synthesis 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 Proceduresand Experimental Results • Subset coding mode • Parameter band stride • Parameter sets • Adaptive smoothing • Conclusion 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 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 • Comparisons:

  20. Experimental Results • 2 phenomena: • Theoretical results larger than experimental results • differential coding schemes • Number of parameter sets increases => theoretical & experimental results decrease • probability distributions

  21. Experimental Results • Distributions of DT data:

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

  23. Parameter Band Stride • Exploit correlation in frequency • Combined with the pairing decision • Flow chart: • 2 successive lossless subsets • 1 single subset

  24. Parameter Band Stride • 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

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

  26. Experimental Results • 2 phenomena: • Theoretical results larger than experimental results • differential coding schemes • Number of parameter sets increases => theoretical & experimental results decrease • probability distributions

  27. Experimental Results • Distributions of DF data

  28. Comparisons of the 2 modules • Using coding mode is more efficient than pbstride • Compare the DT and DF data

  29. Comparisons of the 2 modules • Using pbstride are more overestimated than using coding mode modules • Differential coding schemes

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

  31. Time Resolution • 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

  32. Time Resolution • A border exists • Large difference of parameters • Calculate the differences of backward and forward extractions • Division at time slots with larger differences

  33. Time Resolution • afd

  34. Experimental Results • waveforms

  35. Experimental Results • Additional bitrate: • Complexity:

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

  37. Parameter Smoothing • Flow chart • Compare smoothed coarse with fine quantized parameters • Choose the configure with the least error

  38. Experimental Results • waveforms

  39. Experimental Results • Bitrate variations: • Complexity:

  40. Outline • MPEG Surround Introduction • Proposed Procedures and Experimental Results • Conclusion and Future Work • Demo

  41. Conclusion • Implementation of some encoding procedure in the reference software • 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 weightings • Different parameter weightings • Find a more precise evaluations of quality to fine-tune • Some other tools • Residual coding, temporal shaping…etc

  43. Outline • MPEG Surround Introduction • Proposed Procedures and Experimental Results • Conclusion and Future Work • Demo

  44. Appendix

  45. Filter Banks • 2 stages

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

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

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

  49. Experimental Results

  50. bitrate reduction % without any error

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