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A time-frequency scaling transformation based on the matching pursuit (MP) method is developed for the phonocardiogram (PCG). The MP method decomposes a signal into a series of time-frequency atoms by using an iterative process. The modification of the time scale of the PCG can be performed without perceptible change in its spectral characteristics. It is also possible to modify the frequency scale without changing the temporal properties. The technique has been tested on 11 PCG's containing heart sounds and different murmurs. A scaling/inverse-scaling procedure was used for quantitative evaluation of the scaling performance. Both the spectrogram and a MP-based Wigner distribution were used for visual comparison in the time-frequency domain. The results showed that the technique is suitable and effective for the time-frequency scale transformation of both the transient property of the heart sounds and the more complex random property of the murmurs. It is also shown that the effectiveness of the method is strongly related to the optimization of the parameters used for the decomposition of the signals.

A kernel based on the first kind Bessel function of order one is proposed to compute the time-frequency distributions of nonstationary signals. This kernel can suppress the cross terms of the distribution effectively. It is shown that the Bessel distribution (the time-frequency distribution using Bessel kernel) meets most of the desirable properties with high timefrequency resolution. A numerical alias-free implementation of the distribution is presented. Examples of applications in timefrequency analysis of the heart sound and the Doppler blood flow signals are given to show that the Bessel distribution can be easily adapted to two very different signals for cardiovascular signal processing. By controlling a kernel parameter, this distribution can be used to compute the time-frequency representations of transient deterministic and random signals. This study confirms the potentials of the proposed distribution in nonstationary signal analysis.

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This paper describes the design of a multiprocessor digital signal processing system for applications in power converters such as those that would be used in the next generation of HVdc and SVC [1,2] systems. The system incorporates three high-speed digital signal processors operating independently in parallel, but communicating with one another. The fully programmable system is a powerful device which can implement sophisticated control algorithms in real time for converters. A prototype operating at a clock frequency of 40 MHz has been built for testing and evaluation of control strategies with a laboratory model of an experimental HVdc system based on pulse width modulation (PWM). The results from an illustrative application demonstrate that the design is well suited for real-time digital control of converters and the system is a useful tool for research and development.