OPTICOM OPERA - V 3.5 User Manual page 151

C H A P T E R 6 : T E L E P H O N Y
T E S T I N G
Figure 6.22:
Waveform and VAD Parameters diagram. During this measurement severe distortions were
detected (Drop outs and Front End Clipping)
The screen below shows important results of the PESQ algorithm. It chiefly
shows the MOS score, level measurement results and some additional
information on the delay variation. The PESQ MOS as defined by the ITU
recommendation P.862 ranges from 1.0 (worst) up to 4.5 (best). Below the
PESQ MOS the same value is given mapped to:
•
The full P.800 scale (1..5)
•
To the PESQ-LQ scale
This view presents the final MOS score for the entire files, as well as the MOS
score for Speech and silence separately. The resulting R factor according the e
model is also shown here. Other values given are the minimum, average and
maximum delay in milliseconds, as well as the delay jitter in milliseconds.
Figure 6.23: PESQ Final Result diagram
Using PESQ on OPERA, you can even analyze the behaviour of adaptive jitter
buffers. Of course, OPERA can not look into the gateways, but the result of the
jitter buffer adaptation can be observed as a delay jitter of the audio signal. The
length of the jitter buffer adds linear to the delay of the speech signal. This
means that a delay jump of 100ms is directly related to a jitter buffer adaptation
of this amount (assuming that all the other latencies in the network are
constant). Also you may observe that adaptations occur during active speech,
which results in a worse MOS value. Jitter measurement may give you valuable
information on how to optimize your network.
The delay jitter as measured by OPERA is defined as the maximum and
minimum deviation of the delay from the average delay in ms as is shown in
the final results window. An excerpt of this window can be seen below in
Figure 6.24 .
B A N D V O I C E Q U A L I T Y
145
Final Results
Delay Jitter