Block Diagram

1
Block Diagram
digitizing and source coding
source decoding and D/A
speech
speech
channel coding
channel decoding
interleaving
de-interleaving
burst formatting
burst de-formatting
ciphering
deciphering
modulation
demodulation
2
Source Coding

• source sampling, A/D conversion
• A-law, u-law
• full-rate speech coding
• RPE-LTP (CELP-based coding) 13 Kbps
• half-rate speech coding
• VSELP (CELP-based coding) 5.6 Kbps

3
General CELP Codec
original speech
W(z)
1/Aw(z)
Zero excitation
weighted LPC
1/Aw(z)
1/P(z)
Zero excitation
find D, b
weighted LPC
code -book
1/Aw(z)
1/P(z)
G
find index and G
4
CELP Parameters

• LPC short-term prediction
• LPC is the envelope of spectrum
• LPC can be effectively expressed by LSF
• Pitch long-term prediction
• pitch represents the periodic part tone of the
  speaker
• Excitation
• near white noise

5
RPE-LTP Speech Coding

• Regular Pulse Excitation - Long Term Prediction.
• Encoding is much time-consuming than decoding.
• Complexity around 2 to 3 MIPS.

Excitation Signal
Synthesized Speech
LTP Filter
Inverse LPC Filter
De- emphasis
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RPE-LTP Codec
Input speech
M U X
Weighting Filter and RPE Grid Selection
ADPCM Quantizer
LPC Inverse Filter
Pitch Inverse Filter
Grid Position
LPC Parameter
LPC Analysis
Pitch Analysis
Pitch Parameter
D E M U X
Pitch Synthesis Filter
LPC Synthesis Filter
Residual Decoder
Up- Sampling
Decompressed Speech
Grid Position
Pitch Parameter
LPC Parameter
7
Speech Coding
8
Speech Data Formatting
9
Speech and Channel Coding