The Paraspax method applied on loudspeaker arrays: loudspeaker array-based synthesis of varying spaces including an investigation on how the sound field changes at different position within the array

Abstract

Binaural room impulse responses (BRIRs) describes the transmission from a sound source to a listeners left and right ear, unlike monaural room impulse responses which only contains one channel and therefore sounds the same to both ears. The first method to get BRIRs of a space is by recordings of a sound source using a dummy head with microphones in each ear for different head orientations and positions in the space. This could be both time consuming and costly and therefore research is trying to find new ways that are more practical and includes signal processing. The Paraspax method is a method for parametric spatial audio rendering with 6 DoF based on one monaural room impulse response. The method encodes monaural and spatial parameters offline into a parametric spatial sound field for arbitrary head orientations and room positions. The most important parameters are the amplitudes of the direct sound and up to 10 early reflections with corresponding times and directions of arrival (TOAs, DOAs). The TOAs are simulated from a reflection detection algorithm and the image source model provides the DOAs. These, together with the rest of the parameters, forms the basis of BRIRs synthesized for audio reproduction using headphones. The work of this thesis contains an extension of the BRIR synthesis into a loudspeaker array-based synthesis where the parametrized direct sound and early reflections are distributed over some loudspeakers arranged over a sphere. The resulting sound field is estimated for a listener positioned at different positions inside the loudspeaker array. The authors of the Paraspax have presented the method for a shoebox-shaped room but it is still unknown how it works for other environments and therefore a handful of room impulse responses will be tested. The thesis will answer what the minimum number of loudspeakers in the loudspeaker array is and how the sound field at different listening positions differs from the sound field created at the center of the array. It will also be shown how some parameters of the loudspeaker array influences the sound. Convolving an anechoic drums audio file with the synthesized sound field created by the loudspeaker array acts for virtually place the listener at different positions in the loudspeaker array and the resulting sound represents how the drums are perceived in the different environments of test. The results obtained by the loudspeaker array containing a reduced number of loudspeakers are analyzed and compared with a 84-loudspeaker array. It will be shown that the loudspeaker array is highly dependent on the simulated DOAs, and especially the azimuth angles as it will appear that the loudspeakers should be placed around the listener. If the DOAs of the early reflections are varied enough in azimuth, it shows that three loudspeakers are enough. The sound behaves differently depending on the direction in which the listener moves, but by increasing the number of loudspeakers or the radius of the array, the listener can generally move more freely with the exception of when the TOA differences between the different loudspeakers being too large.