With the virtual reproduction of headphone, the influence of delay time between masker and masked signal on forward masking when sound images are virtually spatial separated in azimuth is studied. The result shows that the thresholds tend to decrease dramatically with the increase in delay time. Furthermore, in case of spatial separation, there are differences of masking thresholds with the maximum about 15 dB. However, when the masker level is 70 dB, the difference of the thresholds increases a little as the delay time increases from 20 ms to 40 ms, which can be explained by the time integration effect and basilar membrane response.
From the point of spatial sampling, spatial interpolation of HRTFs （head-related transfer functions） and signal mixing for multichannel （surround） sound are analyzed. First, it is proved that they are mathematically equivalent. Different methods for HRTFs interpolation are equivalent to different signal mixing methods for multichannel sound. Then, a stricter derivation for the signal mixing of multichannel sound and the law of sine for stereophonic sound is given. It is pointed out that trying to reconstruct lateral HRTFs by adjacent linear interpolation is wrong. And for accurate sound image localization, the conventional equation of adjacent linear interpolation of HRTFs is revised. At last, it is also pointed out that some methods used in the analysis of HRTFs and multichannel sound can be used for reference mutually.
