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CCITT G.726 (ADPCM)

CCITT G.726 (ADPCM). 報告學生 : 張富茂 指導教授 : 尤信程 報告日期 :2002/01/10. Outline. Introduction to the recommendation G.726 Description of the ADPCM algorithm Principles and functional descriptions of the ADPCM encoding and decoding. Encoder. Simplified block diagrams. Decoder.

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CCITT G.726 (ADPCM)

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  1. CCITT G.726 (ADPCM) 報告學生:張富茂 指導教授:尤信程 報告日期:2002/01/10

  2. Outline • Introduction to the recommendation G.726 • Description of the ADPCM algorithm • Principles and functional descriptions of the ADPCM encoding and decoding

  3. Encoder Simplified block diagrams

  4. Decoder

  5. Encoder block schematic

  6. Adaptive quantizer • A 31-, 15, 7- or 4-level non-uniform adaptive quantizer is used to quantize the difference signal d (k) for operating at 40, 32, 24 or 16 kbit/s, respectively.

  7. Operation at 40 kbit/s :I(k)

  8. Quantizer scale factor adaptation • This block computes y (k), the scaling factor for the quantizer and the inverse quantizer. • The basic principle used in scaling the quantizer is bimodal adaptation: • – fast for signals (e.g. speech) • – slow for signals (e.g. voiceband data, tones)

  9. Quantizer scale factor:y(k) The fast and slow scale factors are then combined to form the resultant scale factor:

  10. Adaptation speed control:dms(k)

  11. Adaptation speed control: ap(k)

  12. Adaptation speed control: al(k)

  13. Adaptive predictor and reconstructed signal calculator

  14. a1~a2

  15. b1~b6 For 40kbit/s coding(Recommendation G.726)

  16. Tone and transition detector

  17. Decoder block schematic

  18. Synchronous coding adjustment • The synchronous coding adjustment prevents cumulative distortion occurring on synchronous tandem codings

  19. Conclusion • 在各種語音信號系統，ADPCM 常被用來做聲音編解碼的方法，且CCITT 已提出建議書G.726、G.721，所以有很多市面上的錄音裝置 ，都用這個方法，最好的況狀下，此方法可將傳輸的資料量變成原來的 ¼ • 是否可以達到最佳化，重點在於 quantizer 和 predictor 的設計。

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