In signal processing, a comb filter adds a slightly delayed version of a signal to itself, causing phase cancellations and a spectrum that looks like a comb. It is similar to Ring modulation.
In discrete-time systems, The filter implements the following formula:
- y[n] = ax[n] + bx[n - delay] + cy[n - delay]
It can also be implemented in the continuous-time domain.
There are 2D and 3D comb filters implemented in hardware (and occasionally software) for NTSC television decoders. The filters work to reduce artifacts such as dot crawl.
Other versions of comb filters can be found in networked terrestrial telecommunications systems. However, comb filters are not found in deep space telecommunications systems because of separate system design considerations.