Intermodulation (
IM) or
intermodulation distortion (
IMD) is the
amplitude modulation of
signals containing two or more different
frequencies, caused by
nonlinearities in a system. The intermodulation between each frequency component will form additional signals at frequencies that are not just at
harmonic frequencies (
integer multiples) of either, like
harmonic distortion, but also at the sum and difference frequencies of the original frequencies and at multiples of those sum and difference frequencies.