1. H. Sanneck*, A. Stenger, K. Ben Younes, B. Girod
A New Technique for Audio
Packet Loss Concealment
H. Sanneck*, A. Stenger, K. Ben Younes, B. Girod
Telecommunications Institute, University of Erlangen-Nuremberg D Erlangen, Germany

2. Outline Introduction Time-scale Modification Waveform Substitution
Time-scale Modification with the WSOLA Algorithm
Experimental Results
Conclusions

3. Introduction
In the case of the transmission of waveform-coded audio, packet loss causes signal drop-outs which are very annoying for the listener.
Receiver-only methods
-do not introduce additional processing and data overhead at the transmitter.
-are well suited for heterogeneous multicast environments .

4. Time-scale Modification

5. Waveform Substitution
Repeating a prior segment
Pattern Matching
maximum similarity with the lost segment is assumed.
Pitch Waveform Replication
only one pitch period found in the most recently received packet is repeated through-out the missing packet.
Phase Matching
provides for synchronization on both edges of the substitute.

6. WSOLA Algorithm An appropriate algorithm must perform in real time
may not change the pitch frequency
WSOLA
(Wave-from Similarity Overlap-Add)

7. WSOLA Algorithm
Av　 segments of the input signal at txv ( tx (v-1) + Tx )
Av’　 segments of the input signal at tx (v-1) + Ty
Tx,Ty the time-scaling factor (define Ty = 1/2 L)
L　 the length of Av
L’　 the length of Av’
( L’ = 1/2 L)

8. WSOLA Algorithm

9. WSOLA Algorithm cross-correlation coefficient
the desired time instance

10. Selection of Parameters
Av’ must include at least one pitch period
L’ >= Tp,max
(Tp,max denotes the maximum pitch period of a speech signal)
lout : (N-1)Ty + L
lin : (N-1)Tx + L
the time-scale ratio Ty/Tx is approximately equal to the expansion ratio lout / lin
(l’out - lout) might be employed to minimize loss of information

11. Test Environment Four speech signals with different pitch frequencies
(TM) The new time-scale modification technique
(S) Silence Substitution
(PM) Pattern Matching
(PWR) Pitch Waveform Replication
thirteen non-expert listeners (MOS)
“tinny,metal” “interrupt,clicking” “echoing,reverberating”

12. Results of Subject Performance Tests

13. Results of Subject Performance Tests

14. Conclusions
A new error concealment technique for lost audio packets base on time-scale modification has been proposed.
Experiments show that typical disturbance components of other techniques are reduced and overall quality is improved.