UNIVERSITÉ DE SHERBROOKE - Philippe G OURNAY Senior Research Engineer VoiceAge Corporation...
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UNIVERSITÉ DE SHERBROOKE - Philippe GOURNAY Senior Research Engineer VoiceAge Corporation University of Sherbrooke François ROUSSEAU, Roch LEFEBVRE - ICASSP 2003, Hong Kong, 6-10 April 2003 « Improved Packet Loss Recovery for Prediction- based Speech Coders »
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Transcript of UNIVERSITÉ DE SHERBROOKE - Philippe G OURNAY Senior Research Engineer VoiceAge Corporation...
UNIVERSITÉ DE
SHERBROOKE
-Philippe GOURNAY
Senior Research EngineerVoiceAge Corporation
University of Sherbrooke
François ROUSSEAU, Roch LEFEBVRE
-ICASSP 2003, Hong Kong, 6-10 April 2003
« Improved Packet Loss Recovery for Prediction-based Speech Coders »
UNIVERSITÉ DE
SHERBROOKE
Error propagation (CELP decoder)
One Lost Frame !
Original
Coded
Concealed
Error
UNIVERSITÉ DE
SHERBROOKE
The ACELP coder• Prediction (short- and long-term + quantization)• Analysis-by-synthesis
ErrorMinimization
InnovativeCodebook
Long-termPred. Filter
Short-term (LPC) Filter
PerceptualWeighting
LPC Analysis& Quantization
pulseamplitudes
andlocations
local decoder
weighted error
synthesized speech
error en
speech sn
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SHERBROOKE
Improving 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
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Improving the Robustness (2/4)
• Sender-based Methods
– Forward Error Correction (FEC) Bandwidth
– Multiple Descriptions Bandwidth, Independent Transmission Paths
– Retransmission Delay
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SHERBROOKE
Improving 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
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SHERBROOKE
Improving the Robustness (4/4)
• Summary
– Higher Bit Rate or Delay– Late Packets are Considered as Lost– Recovery Problem Largely Overlooked
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Update (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
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SHERBROOKE
Decoder
Concealment
Recovery
Update
ISGood
Bitsn
ISBad
BFI
UPD
DecodedSpeech
1
0
1
0
Decoder Block
Diagram
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SHERBROOKE
n-1
Concealment Recovery…
A)
B)
C)
…
n
n n+1 n+2 n+3
n-1
n+1 n+2 n+3
n-1 (ii) (iii) n+2 n+3
n
(i)n+1
…
…
…
…
…
“Chronogram” (1 Late Frame)
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SHERBROOKE
Decode(Bitsn-1, Audion-1, BFI=0, UPD=0);
Decode( - , Audion, BFI=1, UPD=0); // Conceal
Decode(Bitsn, - , BFI=0, UPD=1); // Update
Decode(Bitsn+1, Audion+1, BFI=0, UPD=0); // Recover
Decode(Bitsn+2, Audion+2, BFI=0, UPD=0); // ...
...
...
Call Sequence (1 Late Frame)
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SHERBROOKE
Complexity (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
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Sample Waveforms (1/2)
Original
Coded
Concealed
Updated
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Sample Waveforms (2/2)
Original
Coded
Concealed
Updated
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SHERBROOKE
Evaluation 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
Total Cond. 1 Cond. 2 Cond.3 UPD 70% 67% 48% 94%
= 25% 29% 41% 4% STD 6% 4% 11% 2%
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Demonstration Files (AMR-WB)
Original File
AMR-WB (12.65 kbits/s)
Std. AMR-WB (Cond 1) Upd. AMR-WB (Cond 1)
Std. AMR-WB (Cond 2) Upd. AMR-WB (Cond 2)
Std. AMR-WB (Cond 3) Upd. AMR-WB (Cond 3)
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Conclusion
• 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
