signals in both sensor assemblies 33 and 34 thus the detected signal contains components due to both acoustical sources and rigid body motion but acceleration compensated signal contains the acoustic component alone because the rigid body component is cancelled consequently operation in the acceleration compensated mode permits one to separate acoustic sources from rigid body motion further to prevent acoustical signals generated external to the mother e g ambient noise from reaching the external sensor assembly 34 the adjacent region of the cutout 32 is packed with an acoustical insulating material 36 such as wool made from kevlar a flap 37 holds the acoustic insulating material in place the pair of coaxial cables 27 28 or 29 conducts the signals from the sensor stations 24 25 or 26 through connector 30 to the signal processing unit 22 shown in fig1 in an ambulatory monitor the signal processing unit 22 is a small battery operated package mounted on the belt 23 it may be any device which performs the following functions 1 acquiring acoustic signals originating from within the mother 39 s abdomen 2 detecting and cancelling interference contributions e g mother 39 s heartbeat and ambient noise in order to isolate the pressure pulses emitted by the fetal heart 3 detecting fetal movement and 4 analyzing fetal heart signals to determine the state of fetal wellness according to some established criterion experience has revealed that the quality of the signal is sensitive to fetal position and thus the location of a sensor on the mother 39 s body the use of multiple sensors numbering three in the embodiment described here as an example permits.