Flat Lines

R Murray Shafer, in The Soundscape drew my attention to this phenomena.
He identified sounds, almost exclusively associated with the industrial or machine age. The Flat Line in sound is the result of repeated sounds such as motors and machines. Prior to the industrial revolution, sounds made in construction, craft and agriculture consisted of small sounds. Small from the point of view of the sustain element in their sound envelope. Imagine horses hooves, blacksmiths anvils or masons chisels. These would all have been short, abrupt sounds. Now, machines do the work for us and their sound is a monotonous repetition.