Flux is one of two qualities associated with timbre (the other being attack.). Flux refers to the ways in which a sound changes once it has begun playing. In some instruments, the sound of the note changes dramatically after the note is initially sounded (e.g., timpani). Instruments sound different when playing notes in different portions of their range (e.g., a high C on a flute sounds very different foam a C played two or three octaves below). (Sternberg, Barbara, PhD. Music & the Brain. 7-8. CA: Institute for Natural Resources, Home-Study #2320, 2009).