Intermodulation Distortion
Distortion created by a device that is not harmonic with the original signal. Since it is not harmonics of the original signal, intermodulation distortion is often described as "harsh and grating," and tends to be more noticeable than harmonic distortion. Intermodulation distortion is often the result of poor amplifier design or the use of excessive amounts of negative feedback in the circuit. Systems that are fatiguing to listen to often have high rates of intermodulation distortion.