This is probably something standard but it's the first time I encounter it and I don't really know where to find an explanation.
Let's say I produce a sine wave at e.g. 440 Hz on Logic. If I then apply EQ to the track that boosts some random frequency and quickly sweep through the spectrum, after crossing 440 Hz, some of the sound is "carried over" to other frequencies for a short period of time, thus creating a cool effect (which I think I've heard before in sci-fi movies :) )
I guess it's some property of the equalization algorithm, maybe due to the time it takes to Fourier Transform the signal? I would be curious to learn if someone knows why this happens.