Transcript Access IC Lab

Graduate Institute of Electronics Engineering, NTU
Adaptive Differential Pulse Code
Modulation
Instructor: Chia-Tsun Wu.
11/18/2004
ACCESS IC LAB
ACCESS IC LAB
Graduate Institute of Electronics Engineering, NTU
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
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ADPCM encoding algorithm
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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
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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
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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
Please refer to reference [2]
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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
Source
ADPCM encode
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Distortions cont’
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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
http://resource.intel.com/telecom/support/app
notes/adpcm.pdf
http://strawberry.resnet.mtu.edu/pub/Microchi
p/Dsk1/10/appnote/category/pic16/
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