Abstract not available

Naveed Akhtar Malik. / Originally published as thesis (Dept. of Electrical Engineering and Computer Science, Sc.D., 1981). / Bibliography: p. 115-117.

published_or_final_version / Physics / Master / Master of Philosophy

The estimation of power spectral densities is a critical step in many speech enhancement algorithms. The demand for multi-channel speech enhancement systems is high with applications in teleconferencing, cellular phones, and hearing aids. The first objective of the thesis is to develop a general multi-channel framework to solve for the diffuse noise power spectral densities whenever the spatial correlation or coherence matrix is pre-estimated and the number of speakers is less than the number of microphones. The second objective is to develop closed-form analytical solutions. The performance of the developed algorithms is evaluated with pre-existing algorithms using prescribed performance measures.

The estimation of power spectral densities is a critical step in many speech enhancement algorithms. The demand for multi-channel speech enhancement systems is high with applications in teleconferencing, cellular phones, and hearing aids. The first objective of the thesis is to develop a general multi-channel framework to solve for the diffuse noise power spectral densities whenever the spatial correlation or coherence matrix is pre-estimated and the number of speakers is less than the number of microphones. The second objective is to develop closed-form analytical solutions. The performance of the developed algorithms is evaluated with pre-existing algorithms using prescribed performance measures.

The high performance method for obtaining an ARMA model spectral estimate of a wide-sense stationary time series has been found to provide typically superior performance when compared to such contemporary approaches as the Box-Jenkins and maximum entropy methods. In this dissertation, fast recursive algorithmic implementations of the high performance method are developed. They are recursive in the sense that as a new element of the time series is observed, the parameters characterizing an ARMA spectral estimate are algorithmically updated. The number of multiplications and additions required at each recursive stage are of the order p with p being the number of denominator coefficients of the ARMA model. Methods of modification of the data are applied to achieve a significant computational improvement. The development is predicated on utilization of various projection operators. / Ph. D.

A number of topics related to Fourier imaging are investigated. Relationships between the magnitude of errors in the amplitude and phase of the Fourier transform of images and the mean square error in reconstructed images are derived. The differing effects of amplitude and phase errors are evaluated, and "equivalent" amplitude and phase errors are derived. A model of the probability density function of the Fourier amplitudes of images is derived. The fundamental basis of phase dominance is studied and quantitated. Inconsistencies in published counter-examples of phase dominance are highlighted. The key characteristics of natural images that lead to their observed power spectral behaviour with spatial frequency are determined.

This report is guide along simulation of sound sources and orchestra. Basic physical characteristics necessary to the simulation of sound sources are described here. Description of the creation of directivity files in ODEON and theirs conversion from CATT-Acoustic to ODEON are described here too. Acquired directivity files were used for simulation of orchestra and for testing the directivity characteristics to room acoustics parameters.

<p>The performance of different types of nebulisers: Vulkan direct injection nebuliser (Vulkan DIN), direct injection high efficiency nebuliser (DIHEN), microconcentric nebuliser coupled to cyclonic or double pass spray chamber (MCN-C or MCN-DP, respectively) was investigated and compared when used for sample introduction to ICP-MS or ICP-OES. With ICP-OES, in axial viewing mode, intensity distributions across the radius of the plasma (radial intensity profiles) were determined for different spectral lines with Esum 1.85-15.41 eV to determine fundamental plasma properties for various matrices using Vulkan DIN and MCN-C. The results showed that with the MCN-C the ionisation temperature (Tion) was about the same across the measured region of the plasma (±3.0 mm) whereas with the Vulkan DIN the Tion was significantly lower in the centre of the plasma. A large deviation from local thermodynamic equilibrium, as well as deteriorated stability, was observed for the plasma when using the Vulkan DIN.</p><p>With ICP-MS noise power spectra (NPS) were generated to identify sources of noise. NPS showed that the magnitude of white noise for the tested sample introduction systems decreased in the following order: Vulkan DIN > DIHEN > MCN-C > MCN-DP. This order follows the decrease of mean droplet size and span of the size distribution, indicating that the white noise is caused by spatial and temporal non-uniform desolvation and ionisation. Another source of noise arose from the peristaltic pump and the magnitude of pump interference noise decreased in the following order: DIHEN > MCN-C/DP > Vulkan DIN. Mains power interference noise and 1/f noise were lower for the direct injection nebulisers compared to the spray chamber systems. The contribution or effects of these noise components on relative standard deviations of steady-state ion-count rate and isotope ratio measurements is discussed in this thesis.</p><p>Aerosols generated by the Vulkan DIN and the DIHEN were also directly characterised using Particle Dynamic Analysis. The Vulkan DIN produced particles with a mean diameter of ~30 µm and a size distribution between 2-80 µm. With the DIHEN the corresponding values were ~11 µm and 1-40 µm, respectively, with a few particles at 55-78 µm. The mean velocity of particles from the Vulkan DIN was ~10 m s-1 and from the DIHEN ~18 m s-1. The lower velocity allows longer residence time counteracting the effects of the larger droplet size.</p>

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