Professional Audio & Video Blog

Perceptual audio analyse met APx 525

Perceptual audio analyse met APx 525


APx500 v3.0 now supports a PESQ (Perceptual Evaluation of Speech Quality) option for use with APx audio analyzers. Obtain MOS results directly in APx projects,

PESQ is a widely used, enhanced perceptual measurement for voice quality in telecommunications. It was developed by OPTICOM GmbH and forms the basis of ITU-T Recommendation P.862. PESQ is specifically designed for testing voice quality on low bandwidth devices, like mobile phones and smartphones. MOS (Mean Opinion Score) results from PESQ can achieve a very high correlation with results obtainable using human subjects. 

When regular audio tests are not enough

Many voice communications devices, notably mobile phones and VoIP networks, employ limited bandwidth and/or bitrate, and use codecs that significantly alter sound. Despite these accommodations, people can usually understand one another quite well over these systems; this is because the compromises made are selected to allow adequate speech perception despite measurable shortcomings in distortion, frequency response, and other traditional audio measurements.

PESQ simulates the likely results of real human subjects with real speech samples, allowing designers of speech-delivery systems to ensure that real-world customers achieve high levels of product satisfaction.

PESQ methodology

In traditional perceptual measurements, a group of people is assembled and asked to judge the sound quality of various audio clips, typically on a scale from 1 to 5. When all the individual scores are tallied, the result is called the Mean Opinion Score (MOS).

Tests with real human subjects are expensive and time consuming, but these limitations can be overcome by using tools that incorporate algorithms based upon psychoacoustic modeling, such as PESQ. This automation allows for rapid iterations in development as well as efficient production line verification. Measurements obtained are classified as objective because they are unaffected by human temperament or test conditions, and the results are completely repeatable

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