  There is a considerable interest in developing algorithms that can predict
audio quality of perceptually coded signals to avoid the cost of extensive
listening tests during development time. While many established algorithms for
predicting the perceived quality of signals with monaural (timbral) distortions
are available (PEAQ, POLQA), predicting the quality degradation of stereo and
multi-channel spatial signals is still considered a challenge. Audio quality
degradation arising from spatial distortions is usually measured in terms of
well known inter-aural cue distortion measures such as Inter-aural Level
Difference Distortions (ILDD), Inter-aural Time Difference Distortions (ITDD)
and Inter-aural Cross Correlation Distortions (IACCD). However, the extent to
which their interaction influences the overall audio quality degradation in
complex signals as expressed - for example - in a multiple stimuli test is not
yet thoroughly studied. We propose a systematic approach that introduces
controlled combinations of spatial distortions on a representative set of
signals and evaluates their influence on overall perceived quality degradation
by analyzing listening test scores over said signals. From this study we derive
guidelines for designing meaningful distortion measures that consider
inter-aural cue distortion interactions.
