This octave of the electromagnetic spectrum, about a million times higher frequency than the octave our eyes respond to, contains very little energy that originates in our solar system. Almost all of the energy in this band is a result of unbelievably energetic radiation coming from the far reaches of the universe, ‘Cosmic Rays’. Fortunately, they tend not to make it all the way through the approximately 100 miles of air over our heads. As they smash their way through the atmosphere the collisions produce energetic emissions and it is these secondary emissions the Kosmophone responds to. The energy level of each detected event is measured and that information is sent to the MIDI control port of a music synthesizer. The ‘cosmic data’ is not altered or supplemented in any way and would be presumed to be completely random.
The measured distribution of energy values is indeed very uniform and the rate does not vary from local day to night. Apparently the normal output of our sun contains no significant gamma rays (which is a very good thing for us!) but they are produced in bursts during solar flares.
The original site is down, here is a link to Scientific American for similar information :