Echo is an experiment in audience-based musical performance. Most people are able to play simple percussion lines in rhythm at some tempo, so the concept of a percussion ensemble is a fundamental musical idea. Call-and-response structures similarly lie at the foundation of music. Most modern musical performances involve minimal interaction between the "audience" and "performer". One uncommon way to alter this paradigm involves passing instruments out to the audience, such that the performer (or, more accurately in this case, the "organizer") has a more equal role to members of the audience.
In an attempt to face this non-problem, Echo involves a single person who rhythmically informs a group of people with percussion instruments. The structure is similar to a drum circle, but with a significant amount of melodic and rhythmic "urging" or "instruction". Practically implemented, the "main" performer/organizer brings a set of music generating hardware along with a set of large trash cans, rain barrels, and metal drums to hand out to the audience. Some simple tempo cue is created, and the audience is urged to create a rhythmic exchange. Some of the percussion elements contain wireless microphones, and the resulting sound is processed by the organizer. In this way, a unique "informed improvisation" happens which ideally fully engages members of the audience and creates an interesting musical interaction.
A video of a performance of Echo at the CCRMA 2010 Spring Concert can be seen here.