Inter-machine communications have always been kept away from our own communication channel, audible sound in air. There are good reasons for this: the data rates are relatively low when compared to other media (e.g. electric wires, radio) and the sounds tend to be annoying. But as more and more devices support an audio channel for voice or music, that channel becomes a cheap option for transferring arbitrary information among devices that happen to be near each other. Sound is attractive for applications that do not require high bit rates and for which it is expensive to extend the hardware infrastructure with radio or infrared transmitters. Some examples of those applications are: toys; broadcasting information through the sound of TV and radio that can be picked up by devices at home or in the car; transferring names and phone numbers between cell phones; transferring business cards between PDAs; and broadcasting location-dependent information from rooms into PDAs and laptops. Sound also has some natural advantages over other media when security is at stake.

Motivated by the specific characteristics of the aerial acoustic communication paradigm used by humans and other animals, the Digital Voices project explores the use of sound as a communication medium in ubiquitous computing environments. The inter-machine aerial acoustic communications are designed along the following criteria:

• The messages of these communication systems are pleasant to humans. They are either imperceptible or, if perceivable, they sound like music or familiar environment sounds such as birds, wind or water drops.
• The systems are to be deployed in ordinary hardware. We utilize the existing infrastructure for voice, avoiding extra costs.
• The systems are used in ordinary environments. This means that the communication has to be reasonably robust in the presence of noise such as people talking.

Listen to the sound samples on the left. For those of you who like challenges, try to decode the whole of the messages in the "Listen" list on the left. If you can do it, I would like to hear from you! For checking your result and for general information, please contact Prof. Crista Lopes.