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Distance-coded Ambisonics Formats and their Reproduction on Headphones and Loudspeaker Arrays

Authors Riedel, S.
Year 2019
Thesis Type Audio Engineering project
Topic Spatial Audio
Abstract This work introduces distance-coded Ambisonics formats and their reproduction on headphones and loudspeaker arrays. The first simple and practically motivated format proposes two ambisonic streams, a far-field and a near-field stream, to which sounds are distributed according to a distance parameter at encoding stage. In binaural decoding this enables the application of near-field HRTFs with inherent binaural cues which cannot be applied at encoding stage, for example the frequency-dependent increase in interaural level differences compared to far-field HRIRs. Blending between two ambisonic reverberation patterns (model or measured DRIR) is combined with a physically meaningful level attenuation to achieve a plausible distance effect that includes a change in the direct-to-reverberant sound energy ratio. Compatibility with loudspeaker arrays is given by combining the two ambisonic streams into one single stream after introducing differences in level and the two reverberation patterns to retain a relative distance effect. An efficient and more accurate way to render distance is to restrict the effect to the horizontal plane. Therefore, a second format that interprets negative elevation as the distance of a horizontal source is proposed. In binaural reproduction, this format allows for a high spatial resolution in the precomputation of distance-dependent HRTFs and early reflections, applied at decoding stage. Moreover, this format could motivate future research on loudspeaker systems that employ horizontal sound field synthesis (rendering of near-field sources) combined with AllRAD for elevated sources.
Supervisors Höldrich, R.