**** Columbia Network Research Center Student Seminar ****

Title:    Perceived Quality of Packet Audio under Bursty Losses
Speaker:  Wenyu Jiang
When:     Tuesday, October 2nd, 2001 - 3:00-4:00 pm
Where:    CS Conference Room
          Computer Science Dept.
          4th floor, Mudd Building
          Columbia University

ABSTRACT
We examine the impact of bursty losses on the perceived quality of packet
audio, and investigate the effectiveness of various approaches to to
improve the quality.  We first derive a formula to re-compute the
conditional loss probability of a Gilbert loss model when the packet
interval $T$ changes.  Further analysis reveals that FEC works better at a
larger packet interval under bursty losses.  Next, we performed a series
of MOS-based (Mean Opinion Score) listening tests.  We did not find a
consistent trend in MOS when burstiness increases if FEC is not used.
That is, in some occasions MOS can be higher with a higher burstiness.
With FEC, our results confirms the analytical results that quality is
better with a larger packet interval, but $T$ should not be too large to
avoid severe penalty on a single packet loss.  We also find that low
bit-rate redundancy generally produces lower perceived quality than FEC,
if the main codec is already low bit-rate.  Finally, we compare our MOS
results with objective quality estimation algorithms (PESQ, PSQM/PSQM+,
MNB and EMBSD).  We find PESQ has the best linear correlation with MOS,
but the correlation is still not high enough to be used in isolation to
predict MOS.