Filters are essential creative tools. The term filter is defined as a unit that can amplify or attenuate frequencies. The meaning for the audio community has changed however and there are now various filters that make all kinds of changes to any audio signal you feed them.
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Distorting filters became especially famous in the dubstep era. The idea is simple - first distort the signal to generate lots of higher harmonics, then filter some of it away it, and, well, do it again... That gives distorting filters a unique character and makes them useful on pretty much any audio material. But of course, wobbling bases are the signature sound.
Everyone knows how a low-pass filter sounds, it's still used daily by musicians and DJs. But that's just the beginning!
Comb filters have a very distinctive sound. They are essentially microscopic delays and as such they can be taken to a whole new level producing all kinds of mixtures of filtering, delay and reverberation.
Yes, that's correct, vocoders are just filters, pretty complex ones though. And they can do much more than the robotic sounds for which they are so famous.