Originally invented by Reginald Fessenden in 1901 as a means to assist in hearing certain radio transmissions, Heterodyning involves creating two new frequencies from two input frequencies. One of the new frequencies is the sum of the two inputs, and the other is the difference. So, for example, if you have one input tone of 440 Hertz, and another of 643 Hertz, the resulting heterodyned frequencies will be 1,083 Hz (the sum), and 203 Hertz (the difference). The original signa