1. Adaptive Differential Pulse Code Modulation
Instructor: Chia-Tsun Wu.
11/18/2004

2. 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

3. File format for voice data files

4. ADPCM encoding algorithm

5. 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

6. ADPCM decoding algorithm

7. 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)

8. Step size determination

9. Initial and reset conditions
Step size ss(n) = 16
Estimated waveform value X = 0 (half scale)
No DC offset input

10. ADPCM CODEC C example code
Please refer to reference [2]

11. Two examples Example 1: Example 2:
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

12. Distortions
Source
ADPCM encode

13. Distortions cont’

14. 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
Lab 3: Write a 8 to 2 ADPCM CODEC
Resolutions: 8 bits
Encode to 2 bits
Bonus: try to explain and optimal your algorithm to reduce distortions or noise. (need more analysis)

15. Reference http://resource.intel.com/telecom/support/appnotes/adpcm.pdf