Clipping is a non-linear process that produces frequencies not originally present in the audio signal . These frequencies can be harmonic overtones, meaning they are whole number multiples of one of the signal's original frequencies, or "inharmonic", resulting from general intermodulation distortion .    The same nonlinear device will produce both types of distortion, depending on the input signal. Intermodulation occurs whenever the input frequencies are not already harmonically related. For instance, playing a power chord through distortion results in intermodulation that produces new subharmonics .
In terms of how the effects and amp models sound, we give the Zoom G3X a 7 out of 10. Most effects sound great and very convincing. All but the most discerning tone snobs would be able to distinguish them from the “real thing.” As is typical for digital multi-effects units, the quality of the overdrive and distortion effects is sub-par. Conversely, delays, reverbs, and choruses sound pretty great . In fact, one recommendation many users make is to start out with the Zoom G3X, and eventually buy a separate dedicated overdrive or distortion pedal, like a Fulltone OCD or Pro Co RAT2. This comment from an owner sums it up well: