E-Mail IMAGE: The spherical array has 6 microphones sensitive to ultrasound. The ultrasounds are played back to the headphones so that the listener can detect the direction of their source correctly. view more Credit: Ville Pulkki/Aalto University Humans can observe what and where something happens around them with their hearing, as long as sound frequencies lie between 20 Hz and 20 000 Hz. Researchers at Aalto University have now developed a new audio technique that enables people to also hear ultrasonic sources that generate sound at frequencies above 20,000 Hz with simultaneous perception of their direction. The results have been published in Scientific Reports on 2 June 2021.