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In the search for improved reproduction of a classical music performance, the technique of time delay compensation is shown to be a useful tool for balance in recording. This paper investigates the importance and validity of small time adjustments in recordings to compensate for variation in distance between spot microphones and a main stereo pair. Conventional recording techniques, psychoacoustic considerations and technological aspects of the use of delays are researched in order to determine their validity in timbral improvement. / Multiple microphone set-ups are used to record both large orchestral works and smaller-scale classical compositions where auxiliary microphones may be needed to ensure an optimum balance in the final mix. Small time delays are derived from calculations involving the distances between microphones, the speed of sound, and humidity and temperature readings from the hall. Proper synchronization of these delays is desirable to preserve phase coherence and combat comb-filter effects. Precise delay units are used to compile musical exerpts for listening tests. / The results reveal any change in sound quality and provide a basis for investigating both the positive and negative effects through objective study of the value of time delay compensation in the live recording reproduction of classical music performances.

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Automated fusion welding processes play a fundamental role in modern manufacturing industries. The proliferation of joint geometries together with the large permutation of associated process variable configurations has given rise to research into complex system modelling and control strategies. Many of these techniques have involved monitoring of not only the electrical characteristics of the process but visual and acoustic information. Acoustic information derived from certain welding processes is well documented as it is an established fact that skilled manual welders utilise such information as an aid to creating an optimum weld. The experimental investigation presented in this thesis is dedicated to the feasibility of monitoring airborne acoustic emissions of Submerged Arc Welding (SAW) for diagnostic and real time control purposes. The experimental method adopted for this research takes a cybernetic approach to data processing and interpretation in an attempt to replicate the robustness of human biological functions. A custom designed audio hardware system was used to analyse signals obtained from bead on mild steel plate fusion welds. Time and frequency domains were used in an attempt to establish salient characteristics or identify the signatures associated with changes of the process variables. The featured parameters were voltage / current and weld travel speed, due to their ease of validation. However, consideration has also been given to weld defect prediction due to process instabilities. As the data proved to be highly correlated and erratic when subjected to off line statistical analysis, extensive investigation was given to the application of artificial neural networks to signal processing and real time control scenarios. As a consequence, a dedicated neural based software system was developed, utilising supervised and unsupervised neural techniques to monitor the process. The research was aimed at proving the feasibility of monitoring the electrical process parameters and stability of the welding process in real time. It was shown to be possible, by the exploitation of artificial neural networks, to generate a number of monitoring parameters indicative of the welding process state. The limitations of the present neural method and proposed developments are discussed, together with an overview of applied neural network technology and its impact on artificial intelligence and robotic control. Further developments are considered together with recommendations for future areas of research.

The work presented here utilises features of laser generated ultrasound for the detection of defects in solids. Ultrasound is generated noncontactively by this method and likewise many of the detection devices used do not require direct coupling to the test pieces, thus acoustic pulses with high frequency components are able to be produced and monitored on a range of samples. Steel samples coated with between 3 and 7mm of plasma-transferred arc depositions are examined for bond quality via measurements of attenuation caused by porosity in the coatings, found to be related to weld current. Surface breaking cracks, (of depth < 3mm), in such claddings are quantitatively detected by a method which utilises Rayleigh pulses. A two sided automated scanning system is described which examines samples for subsurface defects. Results from the examinations of a dural test piece, plasma sprayed steel bars and carbon fibre composite samples are presented. Resolution of defects is shown to be within 0.5mm for a 1mm thick section of the composite material. A second scanning technique, requiring access to only one sample face, is presented which employs an interferometer for detection and is thus a truly remote system. Laminar flaws are modelled using flat-bottomed holes, the dimensions of which are measured using the resonance of the bodies. A theoretical investigation using various boundary conditions suggests possible applications for quantitative NDE of structures with well defined natural vibration frequencies. The propagation of acoustic transients in plates is also examined. Possible future work concerning laser/ultrasonic NDE is discussed.