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Analysis and Re-Synthesis of Directional Spatial Impulse Responses

Authors Hostniker, K.
Year 2011
Thesis Type Diploma thesis
Topic Spatial Audio
Keywords Ambisonics, audio recording, surround sound, technical acoustics, audio reproduction, acoustics, 3D sound, signal processing
Abstract In this thesis the analysis of measured directional spatial impulse responses and their re- synthesis with improved spatial image sharpness is discussed. For both the direct sound and early reflections, the time of arrival is determined by the detection of transients occurring in the impulse responses. Several approaches are compared. Further analysis and re-synthesis is based on the principle of Directional Audio Coding (DirAC). In the analysis phase, the frequency dependent directional information of the transients and the diffuseness of the signals are established by means of energy calculations. The measured results are compared with a room-acoustic simulation. Furthermore, it is shown that the SoundField SPS200 Ambisonics B-Format microphone, used in this thesis, shows deviations in the direction detection of source positions due to differences in re- cording quality. These deviations occur at higher frequencies, when half the wavelength of the incident sound field coincides with the distance between the microphone capsules, or the sound incidence is 45°. The data obtained from the analysis is applied to the re-synthesis. During re-synthesis, encoding of the impulse responses in higher order Ambisonics is focused on particularly. The non-diffuse parts of the impulse responses are re-synthesized through different weighting of the Ambisonics channels, and the dif- fuse parts are re-synthesized independently by decorrelation. Furthermore, a possible transfer of room acoustic properties is discussed. In addition to capturing both the acoustic properties of the source room and the reproduction room, additional provisions and assumptions need to be taken into account.
Supervisors Sontacchi, A.