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Chapter 12 MPEG-2 Audio

Chapter 12 MPEG-2 Audio. Index. Goal MPEG-2 LSF , MPEG-2.5 Mutichannel MPEG-2 BC. Goals. Address low sampling frequencies Low data rate over internet MPEG-2 LSF , MPEG-2.5 Muti-channel extensions MPEG-2 BC. MPEG-2 LSF , MPEG-2.5. Sampling rate

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Chapter 12 MPEG-2 Audio

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  1. Chapter 12 MPEG-2 Audio

  2. Index • Goal • MPEG-2 LSF , MPEG-2.5 • Mutichannel • MPEG-2 BC

  3. Goals • Address low sampling frequencies • Low data rate over internet • MPEG-2 LSF , MPEG-2.5 • Muti-channel extensions • MPEG-2 BC

  4. MPEG-2 LSF , MPEG-2.5 • Sampling rate • MPEG-2 LSF: 24 , 22.5 , 16 kHz • MPEG-2.5 : 12 , 11.025 , 8 kHz • MP3 • MPEG-2.5 Layer3 extensions • 其餘與 MPEG-1 大都相同 • Bitstream & coder

  5. MPEG-2 LSF , MPEG-2.5 • Fig.1 p.316 • ID • 00: MPEG-2.5 01: reserved • 11: MPEG-1 10: MPEG-2 LFS

  6. Muti-channel • 5.1 channel configuration (3/2/.1) • 5 full channel – 20kHz • 3 – front • 2 – side & rear • 1 frequency enhancement channel , LFE – 200Hz • Enable high-level sounds at frequencies below 200Hz • See Fig.2 p.319

  7. Muti-channel • Challenge • Minimize data rate without sacrificing audio quality • In order to increases PCM sample precision • High sampling rate : 44.1 48 96 192 kHz • Long sample word length: 16 - 24 bits • See table 2 p321

  8. MPEG-2 BC • Backwards compatible with MPEG-1 • Provide mono- and two-channel info concurrently with muti-channel • X: need large data capacity • Embrace backward matrixing technique • MPEG-2 BC • O: low data capacity ( 與上面比較 ) • X: constrains the design of coder • X: unmasking of quantization noise on dematrixing stage • ?? 我看不懂 在p323倒數最後一段

  9. MPEG-2 BC • Matrixing • Lo = c ( L + a C + b Ls ) • Ro = c ( R + a C + b Rs ) • a = b = 1/sqrt(2) , c = 1 / ( 1 + sqrt(2) ) • Fig.3 p323

  10. MPEG-2 BC • Bitstream Format • Fig 4 5 6 7 p325 p326 • 課本也沒多說 • The mutichannel field is stored in the ancillary data portion of the mpeg-1 bitstream • 是否用extension part : • If mutichannel data rate exceeds the MPEG-1 data rate • Ext Bitstream Present bit: fig 6

  11. MPEG-2 BC • Mutilingual channels • Fig 9 p327: • 就只是把 mutilingual 也放進 encoder 裡 • 最多支援 7 個

  12. MPEG-2 BC • Encoding Process Fig 10 p.329 • 幾乎跟 MPEG-1 相同 • Matrixing • Transmission channel allocation • Dynamic crosstalk • 如何把聲音分佈到不同的聲道去

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