resultant tone

noun
  1. a musical sound sometimes heard when two loud notes are sounded together, either lower in pitch than either (differential tone) or higher (summational tone)
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012