Undertone or Undertones may refer to:
Examples of woodwind undertones:
Relevance: Ill-tuned lower notes may - as undertones - mess-up the practical sound (tuning) of higher notes.
Separate pipes of a pipe organ or of a GHB versus the pipe chanter - that is the drones - should not be practically discussed as undertones; they can be turned on and turned off, so each separate pipe is considered to produce its' own sound(s).