Sit quietly in each of your friend's homes, in your office, in any space that you have access to. Listen to the unique sound of the air ducts and ventilation systems - the heater, central air, a toilet duct - any where that air is exchanging, either naturally or by mechanical means. The sound can be soothing or cantankerous, demure or disturbing, but each space has a distinctive soundspace remarkably unlike the others. Field recording/constructionist Eric La Casa has a fascination with these ducts and ventilation systems, which he refers to as aeraulic networks.

air.ratio is about the investigation of these spaces. La Casa explains that the work isn't strictly scientific, but that since being drawn to a particularly interesting bathroom vent in 1994 he's wanted to document their sonic and musical qualities. With a boom and a pair of condenser mikes he chose several locations in Paris and looked for interesting sources of ventilation. The goal was to record the sound as purely as possible, devoid of other environmental distractions or external sound movements. In this he succeeds: the resulting recordings are sonically rich, fascinating for their complex overtones and harmonies, throaty voices, placid countenances or threatening menace, or for their sheer presence and hypnotic character.

In all the CD presents 30 two minutes recordings of ventilation systems. The listener is taken into a variety of locations, including an apartment in Paris, into Radio France, The European Hospital Georges Pompidou and a contemporary art center. Two minutes seems a good length to give the listener time to understand each sound, but not too long to become bored by any. La Casa organized the tracks by classification of ventilation structure, such as "insulated rectangular right conduit" or "air-vent extraction-mechanically controlled ventilation" (11 examples) but explains that his sequencing is essentially arbitrary, and encourages experimentation with the material for various ends. The 30 recordings are book-ended by a 60 second composition sequencing all 30 recordings, normalized into a coherent and quickly breathing work. The CD ends with a minute of silence, La Casa hoping that the listener will clear his head and contemplate the relationship of sound and musical construction. A truly fascinating exhibition.