The experience

To re-create natural sound, in which we ‘hear’ direction and distance, we first need to understand the nature of the signal processing task. Experiencing the world in three dimensions is something we take for granted, but like so many of our natural abilities, the way we are equipped to hear in three dimensions is an amazing piece of biological engineering.

Our ears and our head act as a directionally dependent acoustic antenna system. Incoming sound waves are modified before they reach the eardrum by diffractive effects around the head, and by the direction-dependent resonant properties of the outer ear.

These effects, together with very small time-delays between the arrival of sounds at the individual ears (the inter-aural time delay, or ITD) form the basis for the brain's calculation of direction and distance.

It's not too hard to see how natural selection helped us to develop this extraordinary audio-processing power. Clearly, individuals who could not sense from which direction a predator was moving, nor how fast it moved, might well not survive. The human race has evolved with extraordinary hearing capabilities.

The challenge for Sonaptic has been to use the limited sound reproduction capabilities of mobile devices to recreate a natural, three-dimensional soundscape for the brain with depth and directional qualities, while filtering out as much unwanted sound as possible.