Favorite Chicago Sounds a collaborative web site designed to showcase unique audio portraits of Chicago and mirror what Chicagoans think about their city's soundscape.
The CTA Sound Project a collection of experimental sound pieces created by Chicago musicians and sound artists Justin Petertil and Seth Vanek. The pieces attempt to recreate the aural experience of using public transit in Chicago
The Contraphonic Chicago Sound Series Their aim is to aurally illustrate the historic and modern mechanisms of the Working City.
WWW.Chicago-L.Org From train horns and beeps to station announcements to cab signals to the squeal of the train wheels, this archive has sound files that will be instantly recognizable to any seasoned "L" rider
Audible Frequency From 2002 through May 2005, Alicia Frantz shared her obsession with sound through a beautiful web site called audiblefrequency.  Though she is no longer with us, her recordings and descriptions of them are