Vertical Stereophonic Localization in the Presence of Interchannel Crosstalk: the Analysis of Frequency-Dependent Localization Thresholds

Abstract

Listening tests were conducted in order to investigate the frequency dependency of localization thresholds in relation to vertical interchannel crosstalk. Octave band and broadband pink noise stimuli were presented to subjects as phantom images from vertically arranged stereophonic loudspeakers located directly in front of the listening position. With respect to the listening position the lower loudspeaker was not elevated; the upper loudspeaker was elevated by 30• . Subjects completed a method of adjustment task in which they were required to reduce the amplitude of the upper loudspeaker until the resultant phantom image matched the position of the same stimulus presented from the lower loudspeaker alone. The upper loudspeaker was delayed with respect to the lower by 0, 0.5, 1, 5, and 10 ms. The experimental data demonstrated that the main effect of frequency on the localization threshold was significant, with the low frequency stimuli (125 and 250 Hz) requiring significantly less level reduction (less than 6 dB) than the mid-high (1, 2, and 8 kHz) frequency stimuli (9-10.5 dB reduction). The main effect of interchannel time difference (ICTD) on the localization thresholds for each octave band was found to be non-significant. For all stimuli interchannel level difference (ICLD) was always necessary, indicating that the precedence effect is not a feature of median plane localization.

The Reduction of Vertical Interchannel Crosstalk: The Analysis of Localisation Thresholds for Natural Sound Sources

“…At the localisation threshold then, this difference is not sufficient enough to be interpreted as an elevation difference and therefore the main layer only and phantom image conditions are perceived as being in the same location. Based on this hypothesis, it can be argued that the primary mechanism used for the subject's localisation threshold judgment might be the relative spectral energy weighting between the main and height layers in head-related transfer function (HRTF), rather than being related to the fine spectral details of the sound source, which agrees with a previous study conducted by the authors [10]. It should be noted, however, that the ear input spectra are dependent on the subject and that it is therefore difficult to generalise HRTF characteristics.…”

“…That ICLD was always necessary to reach the localisation threshold for the oboe source, despite there being no significant difference in perceived elevation between the 0 dB and main layer only conditions, might be explained by an alternative hypothesis proposed by the authors [10]. When sound source presentation shifts from main layer only to vertical phantom image, a key difference is an increase in perceived VIS.…”

“…In a more recent study conducted by the authors [10], it was demonstrated that localisation thresholds have a frequency dependency. Octave bands of pink noise, with centre frequencies ranging from 125 Hz to 8 kHz, as well as broadband pink noise, were presented to subjects from vertically-arranged stereophonic loudspeakers in an anechoic chamber.…”

“…The predominant energy of the oboe source, for example, was in the range of 600 Hz-2 kHz, with notable peaks around 700 Hz and 1.5 kHz, whilst that for the conga ranged from 150 to 500 Hz. Given that in [10] it was reported that the localisation thresholds for low frequency octave bands were significantly higher compared to those for the mid-high frequency bands, it was thought that these two sources in particular would be beneficial in analysing the source dependency of localisation thresholds for natural sound sources. The speech source was chosen due to its broadband nature.…”

The Frequency and Loudspeaker-Azimuth Dependencies of Vertical Interchannel Decorrelation on the Vertical Spread of an Auditory Image

“…A similar elevation effect for the 8 kHz octave-band (when presented in vertical stereophony) was seen by Wallis and Lee [43], who investigated the heightchannel gain reduction required to localize stereophonic octave-band conditions at the height of a monophonic reference (the lower loudspeaker only) [44]-in the case of the 8 kHz octave-band, this was found to be around a -9 dB reduction.…”