Determining the subjective speech quality of a transmission system has always been an expensive
and laborious process. Now the tool described in ITU-T Rec. P.862
Perceptual Evaluation of Speech Quality - PESQ will provide a rapid
and repeatable result in a few moments.
PESQ is an objective measurement
tool that predicts the results of subjective listening tests on
telephony systems. PESQ uses a sensory model to compare the original,
unprocessed signal with the degraded signal from the network or
network element. The resulting quality score is analogous to the
subjective "Mean Opinion Score" (MOS) measured using panel tests according to
ITU-T P.800. The PESQ scores are calibrated using a large database of subjective tests.
The ITU-T selection process that
resulted in the standardisation of PESQ involved a wide range of
conditions, with demanding correlation requirements set to ensure
that it has good performance in assessing conventional fixed and
mobile networks and packet-based transmission systems.
Since ITU-T Rec. P.862
was released two further mappings of the PESQ score have been created.
PESQ-LQ modified the score to improve correlation with subjective
test results at the high and low ends of the scale where the raw
PESQ score was found to be less accurate. A new mapping described
in ITU-T Rec. P.862.1 has been released that further modifies the
raw score and is believed to better correlate to subjective test.
PESQ-LQ and P.862.1 mappings are determined and displayed in DSLA
and SPA measurements.
PESQ takes into account coding distortions, errors, packet loss,
delay and variable delay, and filtering in analogue network components.
The DSLA and user interface have been designed to provide a simple
access to this powerful algorithm, either directly from the analogue
connection or from speech files recorded elsewhere.
The performance of a network or a network element can be fully
characterised using the Digital Speech Level Analyser and PESQ.
Whilst it is possible to use phonetically balanced sentences and
other test patterns, accurate and repeatable measurements of the
active speech level, activity, delay, echo, noise and speech quality
can be obtained quickly using the artificial speech test stimulus
in different languages. A graphical mapping of the errors provides
a useful insight into how the signal has been degraded.
This powerful test tool can be deployed in many different areas of a business, on any speech carrier technology:
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In the research laboratory; providing rapid feedback on promising areas of signal processing development,
validation of design implementation, ranking alternative design solutions, providing a higher degree of
confidence before submission to subjective testing
-
In network equipment evaluation; comparing different vendor offerings and determining their impact on network
performance
-
In network installation and rollout of new technologies; ensuring that the desired speech quality is being
delivered as the network complexity and loading increases
-
In troubleshooting network and customer problems; determining the scale of the problem, the effectiveness of
the solution
-
In sales and marketing; demonstrating the excellence of a new product, assuring the customer of the system
performance
Malden Electronics is committed to the development of cost effective
tools to measure all aspects of speech transmission. The integration
of the Perceptual Evaluation of Speech Quality into the Digital
Speech Level Analyser represents another breakthrough in speech
quality measurement technology.
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