  This work introduces a feature extracted from stereophonic/binaural audio
signals aiming to represent a measure of perceived quality degradation in
processed spatial auditory scenes. The feature extraction technique is based on
a simplified stereo signal model considering auditory events positioned towards
a given direction in the stereo field using amplitude panning (AP) techniques.
We decompose the stereo signal into a set of directional signals for given AP
values in the Short-Time Fourier Transform domain and calculate their overall
loudness to form a directional loudness representation or maps. Then, we
compare directional loudness maps of a reference signal and a deteriorated
version to derive a distortion measure aiming to describe the associated
perceived degradation scores reported in listening tests. The measure is then
tested on an extensive listening test database with stereo signals processed by
state-of-the-art perceptual audio codecs using non waveform-preserving
techniques such as bandwidth extension and joint stereo coding, known for
presenting a challenge to existing quality predictors. Results suggest that the
derived distortion measure can be incorporated as an extension to existing
automated perceptual quality assessment algorithms for improving prediction on
spatially coded audio signals.
