  The Perceptual Evaluation of Audio Quality (PEAQ) method as described in the
International Telecommunication Union (ITU) recommendation ITU-R BS.1387 has
been widely used for computationally estimating the quality of perceptually
coded audio signals without the need for extensive subjective listening tests.
However, many reports have highlighted clear limitations of the scheme after
the end of its standardization, particularly involving signals coded with newer
technologies such as bandwidth extension or parametric multi-channel coding.
Until now, no other method for measuring the quality of both speech and audio
signals has been standardized by the ITU. Therefore, a further investigation of
the causes for these limitations would be beneficial to a possible update of
said scheme. Our experimental results indicate that the performance of PEAQ's
model of disturbance loudness is still as good as (and sometimes superior to)
other state-of-the-art objective measures, albeit with varying performance
depending on the type of degraded signal content (i.e. speech or music). This
finding evidences the need for an improved cognitive model. In addition,
results indicate that an updated mapping of Model Output Values (MOVs) to
PEAQ's Distortion Index (DI) based on newer training data can greatly improve
performance. Finally, some suggestions for the improvement of PEAQ are provided
based on the reported results and comparison to other systems.
