Title: Improved Packet Loss Recovery for Predictionbased Speech Coders
1 Improved Packet Loss Recovery for
Prediction-based Speech Coders
- Philippe GOURNAY Senior Research
Engineer VoiceAge Corporation University of
Sherbrooke François ROUSSEAU, Roch
LEFEBVRE - ICASSP 2003, Hong Kong, 6-10 April 2003
2Error propagation (CELP decoder)
Original Coded Concealed Error
One Lost Frame !
3The ACELP coder
- Prediction (short- and long-term quantization)
- Analysis-by-synthesis
4Improving the Robustness (1/4)
- Concealment
- Q What to do when a (Binary) Frame is Missing ?
- A Compute a Replacement (Speech) Frame
- Recovery
- Q What to do when the Frames are Received Again
? - A Control Error Propagation
5Improving the Robustness (2/4)
- Sender-based Methods
- Forward Error Correction (FEC)
- Bandwidth
- Multiple Descriptions
- Bandwidth, Independent Transmission Paths
- Retransmission
- Delay
6Improving the Robustness (3/4)
- Receiver-based Methods
- Frame Loss Concealment
- Limited Effectiveness
- Interpolative Update of the Decoder Internal
State - Very Limited Effectiveness
- Playout Buffering
- Additional Delay, Speech Rate Adaptation
7Improving the Robustness (4/4)
- Summary
- Higher Bit Rate or Delay
- Late Packets are Considered as Lost
- Recovery Problem Largely Overlooked
8Update (Basic Idea)
- The concealment method does not correctly update
the Internal State (I.S.) of the decoder - We keep a copy of the past (Good) I.S. of the
decoder before the concealment - We use the late frame to update the I.S.,
starting from the past (Good) I.S. - Smooth transition between Concealment and
Recovery - Best when done in the excitation domain
9Decoder Block Diagram
10Chronogram (1 Late Frame)
Concealment
Recovery
A)
n-1
n
n1
n2
n3
n1
n2
n3
n
B)
n-1
(i)
n
n1
C)
n-1
(ii)
(iii)
n2
n3
11Call Sequence (1 Late Frame)
12Complexity (1 Late Frame)
- Memory
- One Copy of the Internal State
- AMR-WB roughly 1.5 k-octet
- Processing Power
- Two Additional Decoding of the Excitation
- AMR-WB equivalent to decoding one frame
13Sample Waveforms (1/2)
Original Coded Concealed Updated
14Sample Waveforms (2/2)
Original Coded Concealed Updated
15Evaluation Results (AMR-WB)
- Cond. 1 One Late Frame / 10 Frames
- Cond. 2 One Lost Frame One Late Frame / 15
Frames - Cond. 3 Three Consecutive Late Frames / 20 Frames
16Demonstration Files (AMR-WB)
17Conclusion
- Using Late Frames Substantially Improves the
Recovery of the Decoder - Update the Internal State of the Decoder
- Some smoothing is required between the
Concealment and the Recovery - In a VoIP environment
- More Robust against Jitter, with no Increase in
Delay - Less Delay, with no Quality Degradation