Abstract
Reproduction of high quality spatial sound has gained considerable importance with the recent technology developments in the fields of virtual and augmented reality. Recently, the reproduction of binaural signals in the Spherical-Harmonics (SH) domain has been proposed. This is performed by using SH representations of the sound-field and the Head-Related Transfer Function (HRTF). These processes offer the flexibility to control the reproduced binaural signals, by manipulating the sound-field or the HRTFs using algorithms that operate directly in the SH domain. However, in most practical cases, the binaural reproduction is order-limited, which introduces truncation error that has a detrimental effect on the perception of the reproduced signals, mainly due to the truncation of the HRTF. A recent study showed that pre-processing of the HRTF by ear-alignment reduces its effective SH order, which may be beneficial for alleviating the above effect. In this paper, a method to incorporate the pre-processed ear-aligned HRTF into the binaural reproduction process is presented. The method uses Ambisonics representation of the sound-field formulated at the two ears, and is denoted here as Bilateral Ambisonics. The proposed method leads to a significant reduction in errors due to the limited-order reproduction, which yields a substantial improvement in perceived binaural reproduction quality even with SH as low as first order.
Highlights
B INAURAL technology plays an important role in many applications, such as virtual and augmented reality [1], architectural acoustics [2] and hearing science [3]
Binaural signals can be obtained using microphones placed at the ears of a manikin, in which case the sound-field and the HeadRelated Transfer Function (HRTF) are jointly captured, and the reproduced binaural signal is limited to the specific recording
On the other hand, using the Basic+Magnitude Least-Squares (MagLS) Ambisonics reproduction, orders N = 1 and 2 are significantly different from the reference in all audio source signals, and with Castanets, even order N = 4 is significantly different from the reference. This further demonstrate the perceptual benefits of Bilateral Ambisonics compared to Basic+MagLS Ambisonics. Both objective and subjective results presented in this paper suggest that Bilateral Ambisonics reproduction can produce high quality virtual sounds using relatively low-order reproduction
Summary
B INAURAL technology plays an important role in many applications, such as virtual and augmented reality [1], architectural acoustics [2] and hearing science [3]. In [24], Zaunschirm et al presented a method that uses a preprocessed HRTF, obtained by means of frequency-dependent time-alignment, to reproduce binaural signals in the SH domain using constrained optimization They suggested pre-processing of the HRTF by removing its linear-phase component at high frequencies. The Binaural B-Format is formulated for an arbitrary SH order, enhancing its efficacy, and incorporates the ear-aligned HRTF, which preserves the HRTF phase information This method, denoted as Bilateral Ambisonics reproduction, significantly reduces the truncation error. The contributions of this paper are as follows: 1) Mathematical formulation of the Bilateral Ambisonics reproduction by incorporating the ear-aligned HRTF This generalizes the Binaural B-Format for an arbitrary SH order (Section III).
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