This paper introduces difference-spectrum filters that can be used to control the perceived vertical direction of a sound source presented from ear-level loudspeakers. The difference-spectrum filter was designed to mimic the macroscopic changes in the spectral envelope of head-related transfer functions (HRTFs) between a target elevation angle and the ear-level elevation (0?), where the HRTF envelopes were obtained from averaging an extensive collection of individual HRTFs in a database. Localization tests were conducted to evaluate the effectiveness of difference-spectrum filters on elevation perception, which showed a promising result in the two-channel stereophonic condition for the virtual sound source. The perceived elevation correlated well with the target elevation angle of difference-spectrum filters in the stereophonic condition, although a weak correlation was observed in the monophonic condition. Thus, the test results show that difference-spectrum filters can create robust illusory elevation perception and enable vertical direction control over a wide range of elevation angles in stereophonic loudspeaker reproduction.
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