A complex form of distortion occurring when two signals at different frequencies are produced at the same time creating additional signals at various other frequencies and at various amplitudes. New signals are created at frequencies found by adding the original two frequencies, by subtracting the original two frequencies from one another, from harmonics of the original two frequencies (although this particular distortion is classified as harmonic distortion and so is not truly a part of intermodulation distortion), from the harmonics of these two newly created frequencies (the sum and difference of the original two), and from the sums and differences of the harmonics. Needless to say, this form of distortion results in a multitude of additional frequency signals beyond the original two produced, and each of these frequencies may be heard distorting the original signal. or clarification, a harmonic is a multiple of an original frequency. For instance, a frequency of 2 kHz would have harmonics of 4 kHz, 6 kHz, 8 kHz, 10 kHz and so on with each harmonic being less powerful or of a lesser amplitude than the original signal and the harmonic preceding it. The 4 kHz harmonic would be less powerful than the original signal and the 6 kHz harmonic would be less powerful than the 4 kHz signal like a downward slope. Harmonic distortion is caused when harmonics of an original frequency are produced. ntermodulation distortion begins with additional frequencies being produced by the sum and difference (addition and subtraction) of two original frequencies. For instance, two frequencies of 2 kHz and 8 kHz may have been produced by an audio system. Intermodulation distortion would create two additional signals at 10 kHz (the sum or addition of 2 and 8 kHz) and 6 kHz (the difference between the numbers or subtraction of 2 from 8 kHz). ach of these new signals, the first parts of intermodulation distortion, would then develop harmonics of their own (creating harmonics from 6 kHz of 12 kHz, 18 kHz and so on while producing harmonics of 10 kHz at 20 kHz, 30 kHz and son on). To further confuse the issue and add even more distortion, these harmonics (the harmonics created from the sum and difference frequencies of the original two frequencies) would then create their own sum and difference distortions (for example, the first harmonics located at 12 kHz and 20 kHz would create a sum frequency of 32 kHz and a difference frequency of 8 kHz). bviously, many additional frequencies are added to the audio output creating a complex pattern of distortion. From the two example frequencies at 2 kHz and 8 kHz would come distortions (additional frequency signals) at 4, 6, 8, 10, 12, 16, and 20 kHz within the range of human hearing and many more beyond our ability to hear. Each of these tones at new frequencies are less powerful or have a smaller amplitude than the original two signals. n the final conclusion, intermodulation distortion (IM distortion) can have a profound affect on an audio signal due to the sheer number of distortions it creates. Always look for audio components with the lowest possible distortion numbers, be it harmonic distortion (THD) or intermodulation distortion (IM).