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Master-Vortrag: Signal-Adaptive Approaches to Sound Field Translation
Shahd Al Hares
Mittwoch, 18. November 2020
With the growing demands for spatial audio, Ambisonics became to attract more attention in both fields of recording and reproduction of sound field. Thus, the demand increased for applying sound field translation that allows the use to move freely in different directions in the acoustic scene. In Higher Order Ambisonics (HOA), the sound field incidence is described in the reference point by a set of mathematical functions known as Spherical Harmonics (SH). However, the reproduction is restricted to the surrounding area of the reference point due to the underlying recording hardware, which can be observed in the Ambisonics domain as bandwidth limitation. In this thesis, an Ambisonics sound field translation is investigated. Recent approaches were proposed that allow the listener to move a few centimeters away from the reference point (3DoF+). Another approach provides further translation of the sound field (6DoF) but requires multiple Shperical Microphones Arrays (SMA) to be used during the recording process.
In this thesis, an enhanced method for sound field translation is proposed. It is based on upscaling the Higher Order Ambisonics (HOA) signal to a higher SH order using Compressed Sensing (CS). CS is a framework that is used to recover a signal from an under-determined linear system. Different aspects of HOA upscaling and sound field translation are studied theoretically and practically. Noise reduction with CS for HOA signals is discussed, and the influence of source distance on the translated signal is investigated in the Near-Field-Compensated Higher Order Ambisonics (NFC-HOA) domain. A systematic comparison between multiple translation approaches, namely plane wave translation and space warping, is performed based on two Monte Carlo experiments. Moreover, a new formula is derived that defines the limits of the upscaling SH order as a function of the normalized translation distance and the initial SH order. Finally, a method is introduced for sound field translation of realistic signals based on upscaling in frequency domain. The method is evaluated in frequency domain for multiple Bark bands.
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