This paper investigates the ability to lateralize low-frequency sound in presence of interfering dichotic noise. This is addressed by measuring the detection and lateralization thresholds of four sinusoidal signals (62.5, 125, 250, and 500 Hz) in presence of uncorrelated pink noise in headphone listening. In lateralization test the signals were positioned to left or right by delaying either of the headphone channels by 0.5 ms. The results show that the lateralization threshold does not depart from detection threshold at frequencies 250 and 500 Hz. Interestingly, below 250 Hz the lateralization threshold rises fast, and at 62.5 Hz, the signal has to be amplified 18 dB from detection level before being lateralized correctly. This suggests that low-frequency ITD decoding mechanisms are easily distracted by random changes in signal phase. This explains at least partly why the direction of subwoofer can not be detected easily in surround sound listening of broad-band signal.
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