This thesis discusses quality assessment of audio communications systems, in particular telephone networks. A new technique for time-delay estimation based on a smoothed weighted histogram of frame-by-frame delays is presented. This has low complexity and is found to be more robust to non-linear distortions typical of telephone networks. This technique is further extended to identify piecewise constant delay, enabling models to be used for assessing packet-based transmission such as voice over IP, where delay may change several times during a measurement. It is shown that equalisation improves the accuracy of perceptual models for measurements that may include analogue or acoustic components. Linear transfer function estimation is found to be unreliable due to non-linear distortions. Spectral difference and phaseless cross-spectrum estimation methods for identifying and equalising the linear transfer function are implemented for this application, operating in the filter-bank and short-term Fourier spectrum domains. This thesis provides the first detailed examination of the process of selecting and mapping multiple objective perceptual distortion parameters to estimated subjective quality. The systematic variation of subjective opinion between tests is examined and addressed using a new method of monotonic polynomial regression. The effect on conventional regression techniques, and a new joint optimisation process, are considered.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:661180 |
| Date | January 2003 |
| Creators | Rix, Antony W. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/14286 |
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