Solar Wind Sonification

In 2010, a team from the University of Michigan used solar wind data from 2003, obtained using NASA’s Advanced Composition Explorer Satellite. Composer Robert Alexander mapped Helium velocity data to a frequency between 20Hz and 6kHz. The resulting frequency was used to control the cutoff frequency of a bandpass filter filtering pink noise and a bandwidth that was held at a constant of 1. The result is a sweeping wind sound. The density of the Helium controls the loudness of the sound. At some points in time, a Coronal Mass Ejection⁠1 occurs. When this happens, the sound is sent through an overdrive effect.

Coronal_mass_ejection_(CME)_May_2013
A Coronal Mass Ejection, as pictured here, is the burst of solar wind and the magnetic field into space. This phenomenon is responsible for the aurora borealis and aurora australis.

Alexander used the carbon state charge distribution to control the amplitude of 6 vocal layers. This creates an ambient atmosphere. The value average of the charge state is sonified by voices in a higher register.

The HE/O (Helium/Oxygen) ratio is represented through a chord built out of triangle waveforms in a high register (the corresponding MIDI values of the frequencies are 108, 103, 98, 110, and 105). The ratio is linked to the amplitude of the chord.

In the global mix, the Coronal Mass Ejection also controls a reverb. When a CME occurs, the reverb will go up fast and recede slowly to the base level, dramatising the effect of the CME.

The data are read with a speed of one rotation every 8 measures and a bpm of 150. The result is a three-minute composition.

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