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Adaptive Differential Pulse Code Adaptive Differential Pulse Code - - PowerPoint PPT Presentation

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Graduate Institute of Electronics Engineering, NTU Adaptive Differential Pulse Code Adaptive Differential Pulse Code Modulation Modulation Instructor: Chia-Tsun Wu. 11/18/2004 ACCESS IC LAB ACCESS IC LAB Graduate Institute of Electronics

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Graduate Institute of Electronics Engineering, NTU

Adaptive Differential Pulse Code Adaptive Differential Pulse Code Modulation Modulation

Instructor: Chia-Tsun Wu. 11/18/2004

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Outline Outline

File format for voice data files ADPCM encoding algorithm ADPCM decoding algorithm Step size determination Initial and reset conditions ADPCM CODEC C example code LAB

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File format for voice data files File format for voice data files

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ADPCM encoding algorithm ADPCM encoding algorithm

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ADPCM encoding algorithm ADPCM encoding algorithm

let B3 = B2 = B1 = B0 = 0 if (d(n) < 0) then B3 = 1 d(n) = ABS(d(n)) if (d(n) >= ss(n)) then B2 = 1 and d(n) = d(n) - ss(n) if (d(n) >= ss(n) / 2) then B1 = 1 and d(n) = d(n) - ss(n) / 2 if (d(n) >= ss(n) / 4) then B0 = 1 L(n) = (10002 * B3) + (1002 * B2) + (102 * B1) + B0

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ADPCM decoding algorithm ADPCM decoding algorithm

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ADPCM decoding algorithm ADPCM decoding algorithm

d(n) = (ss(n)*B2) + (ss(n)/2*B1) + (ss(n)/4*BO) + (ss(n)/8) if (B3 = 1) then d(n) = d(n) * (-1) X(n) = X(n-1) + d(n)

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Step size determination Step size determination

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Initial and reset conditions Initial and reset conditions

Step size ss(n) = 16 Estimated waveform value X = 0 (half scale) No DC offset input

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ADPCM CODEC C example code ADPCM CODEC C example code

Please refer to reference [2]

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Two examples Two examples

Example 1:

Speech: 8 bits resolutions, 22.5K sample rate ADPCM encode to 2 bits per sample

Example 2:

Music: 8 bits resolutions, 22.5K sample rate ADPCM encode to 2 bits per sample

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Distortions Distortions

Source ADPCM encode

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Distortions cont Distortions cont

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LAB LAB

Lab 1: Write a 16 to 4 or 12 to 4 ADPCM CODEC

Sample rate: 8KHz for speech Resolutions: 16 or 12 bits Encode to 4 bits

Lab 2: Write a 16 to 4 or 12 to 4 ADPCM CODEC

Sample rate: 44.1K for music Resolutions: 16 bits Encode to 4 bits

Lab 3: Write a 8 to 2 ADPCM CODEC

Sample rate: 8KHz for speech Resolutions: 8 bits Encode to 2 bits

Bonus: try to explain and optimal your algorithm to reduce distortions or noise. (need more analysis)

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Reference Reference

http://resource.intel.com/telecom/support/app notes/adpcm.pdf http://strawberry.resnet.mtu.edu/pub/Microchi p/Dsk1/10/appnote/category/pic16/