Abstract: A transmitter directs a narrow RF ultrasonic beam through a body cavity to a receiver on the other side of the cavity. The beam is steered to be intercepted by audio signal sources in the body cavity, such as a fetal heart or multiple fetal hearts, which modulate the ultrasonic beam. The received parametric beam is demodulated and filtered to provide a relatively noise free audio reproduction of an audio signal source. In one embodiment, two transmitters are steered independently to direct respective beams to respective receivers to produce two signals and, thus, a binaural audio reproduction of an audio signal source. The audio reproduction is at a maximum when the two beams intersect at the audio signal source.