2024 stock. While some of the sounds on this album could be the noise produced by various electric equipment (fax machine buzz, phone busy tones etc.) this album is actually to provide “a standard by which record playing equipment can be checked for frequency response, and distortion, without equipment other than an oscilloscope and volume indicator.” Recorded and annotated by Peter Bartok. Liner notes include detailed information about each track (frequency) and method of testing.