In signal processing, a comb filter adds a delayed signal to itself, causing signal assembly and disassembly interference. The frequency response of a comb filter consists of a series of regularly spaced spikes, giving the appearance of a comb.
2D and 3D comb filters smooth the delayed signal, thus reducing interference. 2D and 3D comb filters are implemented in hardware (and occasionally software) for PAL and NTSC decoders. The filters work to reduce artifacts such as dot crawl.
Enlarged detail dot crawl.
The 3D comb filter is the most recent filter to reduce signal delay and significantly reduce dot crawl.