Earth’s Magnetic Field: Realizations in Computed Electronic Sound, is a seminal piece of sonification art and electronic music in general. In 1970, composer Charles Dodge, together with three physicists Bruce R. Boller, Carl Frederick and Stephen G. Ungar, sonified the variations in the earth’s magnetic field which in influenced by solar winds.
Mapping
Solar Winds make the earth’s magnetic field fluctuate and these fluctuations are registered in the KP index (see below for a detailed explanation). This index consists of 28 possible values and every three hours, a new value is registered by the system, which results in 2920 values for the year 1961, which was used in the composition. These values were tabulated in a so-called Bartel Musical Diagram. One of the physicists had made a five-line staff representation of the data and mapped the values to both a 7-note diatonic scale as well as a 12-note chromatic scale.
As the pitches were mapped through the Bartel diagram, Dodge focused on working on the rhythm and timbre. The 2920 values were compressed in an 8-minute composition and within those 8 minutes, Dodge used algorithms to organise the rhythmic values. Shields writes: “In the first half of the piece, there would be accelerando-ritardando patterns; in the second half, a fixed tempo within which two patterns, A and B, would alternate, the A pattern having one note to a beat, and the B pattern 2 to 14 notes to a beat.” The B-pattern was derived from the sudden commencements, rises in the values due to solar winds and flares which had a bigger impact on the earth’s magnetic field.
Here is a small excerpt.
Importance for electronic music
Besides its importance in sonification, Earth’s Magnetic Field is an important piece in the electro-acoustic music scene as it is the first piece that explicitly uses comb filters to control the timbre. Dodge used the comb filter in the first part while in the second part he used all-pass filtering. The use of filters is a pure aesthetical choice while pitch and rhythm are dependent on the data.
The composition was produced at the Columbia-Princeton Electronic Music Center, founded in 1959, which was the first centre for electronic music in the United States. Besides Earth’s Magnetic Field, other notable works from the centre are Milton Babbitt‘s Vision and Prayer and Charles Wuorinen‘s Time’s Encomium,
Earth’s Magnetic Field was released in 1970 on Nonesuch Records. It has been reissued by New World Records in a compilation cd of electronic music at the Columbia-Princeton Electronic Music Center and you can buy it here from the editor, or on Amazon USA and Amazon UK. Some streaming services offer the recording as well. And below you can see a version on Youtube.
What is the KP-index?
The KP-index is a global geomagnetic storm index with a scale of 0 to 9. The Kp-index measures the deviation of the most disturbed horizontal component of the magnetic field on fixed stations worldwide with their own local K-index. The global Kp-index is then determined with an algorithm that puts the averages of every station together. The result is the global Kp-index. The Kp-index ranges from 0 to 9 where a value of 0 means that there is very little geomagnetic activity and a value of 9 means extreme geomagnetic storming.
Sonification Art 