Audio Networking

Overview

• It offers fine-grained control over the range of transmission by adjusting the volume.
• Walls of buildings are typically designed to attenuate sound waves, making it easy to contain transmission to a single room (unlike, for example, 802.11).
• It allows existing devices that play or record audio to be networked easily (e.g. voice recorders).

It is different from modem technology in that audio networking should work "over the air", where modems are designed to operate over telephone connections (which have good phase and noise properties compared to air).

Applications

The video above demonstrates an Audio Pick and Drop Interface: an Internet URL is recorded into a PDA via a standard computer speaker. The URL is later retrieved from the PDA by playing it into the computer, and also printed by carrying the PDA to a print server and playing back the recorded identifier. A great advantage of this is that any cheap voice recorder is capable of carrying the audio information (e.g. mobile phone, PDA, dictaphone, etc).	One of the more interesting discoveries during this research is that most computer soundcards do not have good anti-aliasing filters fitted, resulting in them being able to send and receive inaudible sound at upto 24 Khz (assuming a 48 KHz soundcard). We used this to create a set of inaudible location beacons that would allow laptop computers to simply listen using their microphones and discover their current location without any advanced equipment being required!
We devised a scheme of encoding data into mobile phone ringtones while still making them sound pleasant to the ear. This allows us to use the phone network for the video example above: an SMS 'capability' is transmitted to a phone, which can be played back to gain access to a building. Since the data is just a melody, this allows for uses such as parents purchasing cinema tickets online for their children (who dont own a credit card), yet still allowing the children to gain access to the cinema by playing the ringtone capability back (via their mobile phones, common among children).	We observed that audio networking allows URLs to be easily sent over a telephone conversation, and retrieved over a normal high bandwidth connection by the recipient. This gets over the real awkwardness of "locating" someone on the Internet, which is rife with restrictive firewalls and Network Address Translation which is destroying end-to-end connectivity. In contrast, it is trivial to locate someone on the phone network given their telephone number, but harder to perform high bandwidth data transfers (which the Internet excels at).

Sound Samples

• Context-Aware Computing with Sound
  Anil Madhavapeddy, David Scott, and Richard Sharp
  In the Proceedings of the Fifth International Conference on Ubiquitous Computing (UBICOMP-2003), October 2003.
  [PDF]

People

Anil Madhavapeddy	David Scott	Richard Sharp
Computer Laboratory, University of Cambridge	Laboratory for Communication Engineering	Intel Research Cambridge