Background

The brown note is supposed to be the resonant frequency of the human digestive system, somewhere in the sub-sonic range. When played back loudly enough, this note possibly may cause a loss of sphincter control... Different versions of the myth place the frequency between 2 and 20 Hz, and recent variations claim that the effect has been produced at loud rock concerts.

By extension, the term also refers to any infrasound note that can create disorientation or nausea. Not to be confused with the brown noise.