2x440Hz

On one side the frequency rises from 392Hz to 466Hz, on the other side conversely.
You can also hear the beat-frequency changing. (Through the alpha-, beta- and gammawaves, the brainwaves)
The standard-pitch (440Hz) changed the last 250 years from 392Hz (France) and 466Hz (Italy) to nearly 440Hz (London 1938).

Galerie Vestib├╝l, 18.9.2009