DATA-COMPRESSION OF FETAL DOPPLER ULTRASOUND AUDIO SIGNALS USING ZERO-CROSSINGS ANALYSIS

This paper outlines a method of reducing the data rate for transmittin g fetal Doppler ultrasound audio signals. A specific application is ci ted where compression of the fetal Doppler signal is required to trans mit information to cardiotocographs (CTGs) using radio telemetry. The method involves splitting the signal into amplitude and frequency comp onents. The amplitude in represented by samples of the signal envelope whilst the frequency information is represented by the number of zero -crossings within fixed intervals (windows). With a careful choice of window size, it is shown that this method can be used to reproduce the signal with no audible difference when compared with the original wav eform. A reduction in data rate of 15.1 is achieved. (C) 1997 IPEM. Pu blished by Elsevier Science Ltd.