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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 6.16: The Raw PSQM diagram
In PSQM, the silent intervals are taken into account using a weighting factor that
depends on the context of subjective experiments, i.e. the portion of silence
intervals varies from one culture group to the other. As Figure 6.16, three
PSQM values are displayed that use different weighting factors. For European
languages to take the PSQM-W2 value into account is recommended.
Model Output Variable (MOV)
Silence
Sev. Distorted
Time Clipped
PSQM-W0
PSQM-W2
PSQM-W4
PSQM Silence
Table 6.2: MOVs used by the OPERA™ PSQM version, and their interpretation
In subjective assessment of the performance of codecs, the ACR method using
the Listening Quality scale specified in Recommendation P.800 is often used,
giving subjective quality in terms of MOS (see chapter 2). The OMOS value
represents the Objective Mean Opinion Score.
Table 6.3 presents the interpretations of the bars in the diagram shown in
Figure 6.17 (from left to right). The OMOS+ is the PSQM+ result, mapped
to the MOS scale. PSQM+ is a further development of PSQM, optimized for
severe impairments as they occur in the case of VoIP and realistic GSM
connections. OMOS-I is the PSQM result mapped to a full five point MOS
scale, ranging from 1 to 5. This represents an individual, ideal listener. The
average listener will usually not exploit the full range of this scale.
B A N D
V O I C E
Q U A L I T Y
Interpretation
The percentage of silent intervals
during a measurement
The percentage of severely distorted
frames during measurement
The percentage of time clipped
frames during measurement
PSQM according to P.861,
silence weight = 0.0
PSQM according to P.861,
silence weight = 0.2
PSQM according to P.861,
silence weight = 0.4
PSQM value of the silence intervals
131
MOS etc.
Model Output
Variables
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