Both spatial and timbral factors are important in the assessment of the multichannel audio coding systems. The Choi et al. model [1] that extending the ITU-R Rec. BS. 1387-1 [2] to the multichannel audio coding systems, with the use of three spatial features, ITDDist (Interaural Time Difference Distortion), ILDDist (Interaural Level Difference Distortion), and IACCDist (InterAural Cross Correlation Distortion), is such an example. In that implementation, ITDDists were only computed for the low frequency (below 1500Hz) sounds and ILD distortions were only computed for the high frequency components. Such implementation is reasonable under classical duplex theory [3]. However, in the high frequency range, the interaural difference in temporal envelopes is also important in spatial perception, especially in sound localization. A new model to compute the ITD distortions of temporal envelopes in high frequency components is introduced in this paper to investigate the role of such ITD on prediction of perceived spatial quality quantitatively. The computed ITD distortions of temporal envelopes in high frequency components were highly correlated with perceived sound quality. Moreover, when the proposed envelope ITD distortion was included in the prediction model in [1], as one of the multiple features to predict overall sound quality, the overall performance of sound quality prediction was enhanced compared to the model in [1].
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