The 'static', 'whistles', 'thunder', 'wind'
that you hear in Space Vox are Earth Songs ...
Planet Earth is a natural source of radio waves, which surround us all the time.
Although most of these waves are in the acoustic frequency range, they are not
audible by humans. They are electromagnetic waves – not acoustic ones; we
would have “heard” them if we had radio antennas instead of ears.
Radio waves can be detected by our ears if we convert them to sound waves, by
using a very low frequency (VLF) receiver. A VLF receiver consists of an antenna
and a radio amplifier, and it is sensitive to radio waves. After converting
electromagnetic (radio) waves into acoustic (sound) waves, with the same
frequency, the sounds produced by our planet can be “heard”.
These sounds correspond to several types of radio emissions propagating in the
Earth’s atmosphere, ionosphere and magnetosphere. The way these waves
sound, when played through an audio system, defines their name: sferics,
tweeks, whistlers, chorus, and hiss. We also call them “Earth Songs”.