Train whistles keep me company, at night, suspended in sonic glop, massaged by an awareness of the landscape.   Long ago - longer than I can count - Pittsburgh was part of a large, flat plain extending from the Alleghenies to the end of the world.  The Garfield Water tower and the section of Forbes avenue running through  Squirrell Hill are reminders of this original level, when the Allegheny and Monongahela flowed broadly across the plain.   

When the glaciers receded, the flow of water increased and the rivers settled in to the deeper and narrower paths followed today. The Point is the confluence of the two contemporary rivers. If you walk down Murray avenue from Forbes, you are walking in to the vestigial river bed of tributaries that were cut off as the rivers sank further in to the bedrock.

The landscape promotes (provokes) sonic phenomena - the region is shaped like an ancient greek theatre with the Point as the proscenium.  The Point is recognizably significant.  Martin Aurand writes  in The Spectator and the Topographical City:

"Many cultures represent the center as the sacred mountain and axis mundi, the place of connection between the cosmic realms of heaven, earth and the underworld, or as the omphalos, the navel or point of creation.  Pittsburgh is, by its topographical nature, a place of differentiated space, prone to centering." (p12)

Grant Street is a rapid ascent, and forms the lip of the orchestra:  interesting to note that Grant's Hill was perhaps an ancient burial ground and in the late 19th century was lowered significantly to allow smoother roads from the water to the main section of town.

From the stage, two hills on the left (Troy and Observatory) form a wall moving East that is mirrored to the right by Mt. Washington.  Together, these diverging lines are  the walls of an auditorium ending with the back wall at the rise of Penn Hills several miles along the East Liberty plateau.

In an ancient greek theatre, the Parados was an entrance reserved for the chorus to enter the proscenium. Panther Hollow serves as parados for the Pittsburgh auditorium, rising from the Monongahela up in to Oakland and joining with the gullies around Squirrell Hill. 

The landscape modulates sound in two ways.    First, frequency appears to change as an object moves closer or farther.  We are all familiar with the sound of an emergency siren approaching at a higher frequency and then appearing to dropp as it passes.  This is a result of the Doppler effect.   

Second, the shape of a chamber affects the resonant frequencies.  Consider the didgeridoo, which is played by creating a standing wave of air inside a hollowed piece of wood, traditionally Eucalyptus.  Variations in the interior surface cause complex harmonics and overtones. A skilled player can also manipulate the harmonics by changing the shape of their mouth, moving lips and toungue to create a changing cavity.  The same technique is used to Khoomei in the Himalayan polyphonic style.  (Also the basis for a good impression of Marvin the Martian (hat tip to Earrach...))

Trains enter Pittsburgh from the East.  The sound of the engines and the sound of the whistle swirl through Panther Hollow and emerge in to the auditorium of East Liberty.  Machines in the distance are enormous drones:  bagpipes, didgeridoo or wandering throatsingers.  When we hear them sound at night, we are hearing the original noise modulated by movement through the changing resonant chambers created by the landscape.

A few years ago, friends circulated a christmas email that included a recording of a Pittsburgh  factory whistle.  The operator was manipulating the control to play christmas carols.  It must have filled the air for miles, with the same effect that a church bell would have had a thousand years ago before we filled the sonic landscape with other noises.

The recording was made by Tony Schwartz for the Smithsonian Folkways collection.