1. IPTEL'2001, New York, USA1 Lingfen Sun Graham Wade, Benn Lines Emmanuel Ifeachor University of Plymouth, U.K. Impact of Packet Loss Location on Perceived Speech Quality

2. IPTEL'2001, New York, USA2 Outline Introduction Codec's internal concealment and convergence time Perceptual speech quality measurement Simulation system Loss location with perceived quality Loss location with convergence time Conclusions and future work

3. IPTEL'2001, New York, USA3 Introduction End-to-end speech transmission quality –IP network performance (e.g. packet loss and jitter) –Gateway/terminal (codec + loss/jitter compensation) Impact of packet loss on perceived speech quality –Loss pattern (e.g. burst/random) –Loss location (codec's concealment) SCN IP Network Gateway

4. IPTEL'2001, New York, USA4 Introduction (cont.) Previous research on loss location –Concealment performance is speech content related (e.g. voiced/unvoiced) –Analysis based on MSE or SNR for limited codec –Perceptual objective methods only to assess overall quality under stochastic loss simulations Questions: –How does a packet loss location affect perceived speech quality ? –How does a packet loss location affect codec's convergence time (for loss constraint)?

5. IPTEL'2001, New York, USA5 Codec's internal concealment What is codec's concealment? –When a loss occurs, the decoder interpolates the parameters for the lost frame from parameters of previous frames. Which codec has concealment algorithm? –G.729/G.723.1/AMR (main VoIP codecs) –CELP analysis-by-synthesis What are the limitations of concealment algorithms? –During unvoiced(u) or voiced(v) –During u/v

6. IPTEL'2001, New York, USA6 Codec's convergence time What is convergence time? –The time taken by decoder to resynchronize its state with encoder after a loss occurs. It is also called resynchronization time. –For set up loss constraint distance between two consecutive losses for new packet loss metrics What is the relationship between convergence time with loss location, codec type and packet size?

7. IPTEL'2001, New York, USA7 Perceptual quality measurement Transform the signal into the psychophysical representation approximating human perception Calculating their perceptual difference Mapping to objective MOS (Mean Opinion Score) Algorithms: PSQM/PSQM+/MNB/EMBSD/PESQ Reference signal Objective perceptual quality test System/network under test Objective MOS Degraded signal

8. IPTEL'2001, New York, USA8 Simulation System Reference speech Degraded speech with loss Degraded speech without loss perceptual quality measure decoderencoder Bitstream decoder loss simulation convengence time analysis Reference speech Perceptual speech quality analysis with loss location Convergence time analysis with loss location

9. IPTEL'2001, New York, USA9 Speech test sentence is about 6 seconds. First talkspurt (about 1.34 second, above waveform) is used for loss location analysis. Four voiced segments, V(1) to V(4), which can be decided by pitch delay in G.729 codec Speech test sentence

10. IPTEL'2001, New York, USA10 Pitch delay from G.729 codec V(1) V(2) V(3)V(4)

11. IPTEL'2001, New York, USA11 Loss location with perceived quality Each time only one packet loss is created Loss position moves from left to right one frame by one frame Overall perceptual quality is measured from PSQM/PSQM+, MNB and EMBSD Packet size: 1 to 4 frames/packet Codec: G.729/G.723.1/AMR How does a loss location affect perceived speech quality ?

12. IPTEL'2001, New York, USA12 Loss position with quality (1) PSQM+ PSQM Loss positionreference speech degraded speech

13. IPTEL'2001, New York, USA13 Loss position with quality (2) Loss position PSQM+ PSQM reference speech degraded speech

14. IPTEL'2001, New York, USA14 Loss position with quality (3) Loss position PSQM+ PSQM degraded speech reference speech

15. IPTEL'2001, New York, USA15 Loss position with quality (4) Loss position PSQM+ PSQM degraded speech reference speech

16. IPTEL'2001, New York, USA16 Overall PSQM+ vs loss location (G.729) G.729

17. IPTEL'2001, New York, USA17 Overall MNB vs loss location (G.729) G.729

18. IPTEL'2001, New York, USA18 Overall EMBSD vs loss location (G.729) G.729

19. IPTEL'2001, New York, USA19 Overall PSQM+ vs loss location (G.723.1) G.723.1

20. IPTEL'2001, New York, USA20 Loss location with perceived quality Loss location affects perceived quality. The loss at unvoiced speech segment has no obvious impact on perceived quality. The loss at the beginning of the voiced segment has the most severe impact on perceived quality. PSQM+ yields the most detailed result comparing to MNB/EMBSD

21. IPTEL'2001, New York, USA21 Convergence time based on MSE G.729

22. IPTEL'2001, New York, USA22 Convergence time based on PSQM+

23. IPTEL'2001, New York, USA23 Convergence time based on PSQM+

24. IPTEL'2001, New York, USA24 Loss location with convergence time Convergence time is almost the same for different packet size Convergence time for a loss at unvoiced segments appears stable Convergence time shows a good linear relationship for loss at the voiced segments –maximum at the beginning –linear descending –Up bound to the end of voiced segments

25. IPTEL'2001, New York, USA25 Conclusions and future work Investigated the impact of loss locations on perceived speech quality Investigated the impact of loss locations on convergence time The results will be helpful to develop a perceptually relevant packet loss metric. Future work will focus on more extensive analysis of the impact of packet loss on speech content