Abstract
Initial analysis of electromagnetic waves at audible frequencies consisted of playing the recorded data through a loudspeaker. The historical terminology in this field thus resembles an experimental musical score where we can encounter whistlers, noise, hiss, and chorus.
On the basis of measurements by NASA's THEMIS (Time History of Events and Macroscale Interactions during Substorms) spacecraft mission, the authors describe two types of natural electromagnetic waves: chorus and plasmaspheric hiss. They show that plasmaspheric hiss can be interpreted as arising from transformed chorus waves, thus providing important clues as to its origin.