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-91058 Erlangen, Germany

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

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 .

Time-scale Modification

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.

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

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)

WSOLA Algorithm

WSOLA Algorithm cross-correlation coefficient the desired time instance

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

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”

Results of Subject Performance Tests

Results of Subject Performance Tests

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.