From the record notes: "The solar wind may be viewed as pushing against Earth's magnetic field, in turn producing an equal but opposite push on the solar wind. The solar wind is not uniform and consequently any changes in it are quickly reflected at the Earth's surface as changes in the magnetic field ". The Kp index represents the average of the magnetic changes, which are measured at a selected group of magnetic observing stations on Earth and may take on any of 28 distinct values. Every three hours, the observations provide a new value for the index, thereby giving eight values of Kp for each day. As an aid for researchers, the Kp indices are displayed graphically. They look somewhat like musical notation and are popularly called "Bartels" musical diagrams," after their inventor, German geophysicist Julius Bartels. These diagrams are largely responsible for providing the motivation for the music contained in this album. In addition to the Kp indices, the graphs indicate the times of occurrence of "sudden commencements." As the term implies, these are rapid changes of Earth's magnetic field. The sudden commencements are determined by an examination of the detailed data from each magnetic observatory. In a real sense, then, the music on this record represents the sun playing on the magnetic field of Earth.
"The succession of notes in the music corresponds to the natural succession of the Kp indices for the year 1961. Musical interpretation of the magnetic data was originally conceived by Messrs. [Bruce R.] Boller and [Stephen G.] Ungar and implemented by Carl Frederick; the indices were computer-programmed into a form suitable for music synthesis by Stephen Ungar, This musical interpretation consisted of setting up a correlation between the level of the Kp reading and the pitch of the note (in a diatonic collection over four octaves), and compressing the 2,920 readings for the year into just over eight minutes of musical time. An extended interpretation of the Kp index employed in shaping the music for this record embraces the pattern of sudden commencements during 1961. A graph, plotting the highest reading within each segment between the sudden commencements versus the relative length of the segment, was devised to delineate such attributes of the texture as tempo, dynamics, and register in both the larger and smaller dimensions of the work ". The single-line pitch successions on Side One exhibit the diatonic correspondence described above. The polyphonic settings of sudden-commencement sections which comprise Side Two employ an equal-tempered correspondence, with twelve Kp readings to the octave.
"The musical realization of Earth's Magnetic Field was accomplished between June and September of 1970. The computer "instruments" for the performance were programmed by Charles Dodge, using a general-purpose sound synthesis program written by Godfrey Winham at Princeton University. All of the sounds heard in this album were computed into digital form using the IBM/360 model 91 at the Columbia University Computer Center, and were converted into analog form at the Bell Telephone Laboratories.
Earth's Magnetic Field