These are solar sounds generated from 40 days of Michelson Doppler
Imager data and processed by
A. Kosovichev.
The procedure he used for generating these sounds was the following:
He started with
doppler velocity data, averaged over the solar disk, so that
only modes of low angular degree (l = 0, 1, 2) remained.
Subsequent processing
removed the spacecraft motion effects, instrument tuning, and some
spurious points.
Then Kosovichev
filtered the data at about 3 mHz to select clean sound waves (and not
supergranulation and instrumental noise).
Finally, he interpolated
over the missing data and scaled the data (speeded it up a factor 42,000
to bring it into the audible human-hearing range (kHz)).
