Modeling Localization of Amplitude-Panned Virtual Sources in Sagittal Planes

Abstract

Vector-base amplitude panning (VBAP) aims at creating virtual sound sources at arbitrary directions within multichannel sound reproduction systems. However, VBAP does not consistently produce listener-specific monaural spectral cues that are essential for localization of sound sources in sagittal planes, including the front-back and up-down dimensions. In order to better understand the limitations of VBAP, a functional model approximating human processing of spectro-spatial information was applied to assess accuracy in sagittal-plane localization of virtual sources created by means of VBAP. First, we evaluated VBAP applied on two loudspeakers in the median plane, and then we investigated the directional dependence of the localization accuracy in several three-dimensional loudspeaker arrangements designed in layers of constant elevation. The model predicted a strong dependence on listeners' individual head-related transfer functions, on virtual source directions, and on loudspeaker arrangements. In general, the simulations showed a systematic degradation with increasing polar-angle span between neighboring loudspeakers. For the design of VBAP systems, predictions suggest that spans up to 40° polar angle yield a good trade-off between system complexity and localization accuracy. Special attention should be paid to the frontal region where listeners are most sensitive to deviating spectral cues. INTRODUCTIONVector-base amplitude panning (VBAP) is a method developed to create virtual sound sources at arbitrary directions by using a multichannel sound reproduction system [1]. VBAP determines loudspeaker gains by projecting the intended virtual source direction onto a basis formed by the directions of the most appropriate pair or triplet of neighboring loudspeakers. Within that pair or triplet, the loudspeaker signals are weighted in overall level. A problem of VBAP is associated with localization errors, that is, that virtual sources can be localized at directions deviating from the intended directions [2]. In this study we applied an auditory model in order to replicate [2] and investigate the limitations of VBAP with respect to sound localization.We use the interaural-polar coordinate system shown in Fig. 1 to distinguish different aspects of sound localization. In the lateral-angle dimension (left-right), VBAP introduces interaural differences in level (ILD) and time (ITD) and thus, perceptually relevant localization cues [3]. In the polar-angle dimension, monaural spectral features at high robert.baumgartner@oeaw.ac.at; piotr@majdak.com Localization in the polar-angle dimension (i.e., in sagittal planes) is based on a monaural learning process in which spectral features, that are characteristic for the listener's morphology, are related to certain directions [5]. Due to the monaural processing, the use of spectral features can be disrupted by spectral irregularities superimposed by the source spectrum [6]. The use of spectral features is limited to high frequencies (above around 0.7 kHz) because the s...

The Effect of Hearing Loss on Localization of Amplitude-Panned and Physical Sources

“…listener. [13][14][15]17,[20][21][22] Stimuli were 4 Hz amplitude-modulated with 100% modulation depth in sine phase. Four-hertz amplitude-modulation and 100% depth were used to give listeners multiple "looks" at each stimulus.…”

“…Localization errors tend to get larger as the speaker pair or triplet is moved laterally off the sagittal plane (i.e., nearer to the listener's right or left; þ 90 or -90 degrees, respectively), 14 or as the loudspeaker pair is separated by a larger angle. 13 This effect of loudspeaker separation on change in localization errors is most noticeable for amplitude panning in elevation, especially when the loudspeakers are far apart. 13 Research on amplitude panning generally shows that localization errors are smaller for broadband signals (i.e., speech, noise, etc.)…”

“…than for narrowband signals (i.e., single tones, bandpass noise, etc.). [13][14][15][16][17] Research on listeners with normal hearing shows promise for building a virtual space out of a combination of physical and panned sources; however, the perceptual effects of amplitude panning-based virtual sources on listeners with impaired hearing are poorly understood.…”

Sound Source and Loudspeaker Base Angle Dependency of Phantom Image Elevation Effect

“…Existing localization prediction models in the literature [31][32][33] generally assume that the human auditory system determines the direction of sound source by comparing the ear-input spectrum of the source with a set of template spectra for target source directions that are stored in the system; the source will be most likely to be perceived at the direction where the similarity of the template spectrum to the ear-input spectrum is the highest. In the context of phantom source localization in the median plane, Baumgartner and Madjak [34] claims that localization inaccuracy in the vector base amplitude panning (VBAP) [35] is caused by the discrepancy between the HRTF of a phantom source and that of a real source at the target direction.…”

JND-based spatial parameter quantization of multichannel audio signals

“…In some experiments on sound source localization, laser pointer-based methods [33][34][35] are often used to locate the exact location of sound source perceived and pointed by listeners. Since we mainly focus on the difference of perceived virtual sound location between processed and unprocessed multichannel audio excerpts, the listener just needs to tell how about the differences, obvious or not.…”