Today's Lesson

What is comb filtering?

Comb filtering occurs when certain frequencies are either amplified or attenuated within 10 dB of each other by interference from an identical version of the original audio signal that is delayed between 2-30ms.This is important. If the two signals interact outside of those two circumstances, the comb filtering effect does not take place. This is very helpful to understand when trying to avoid comb filtering. It is called comb filtering because the resulting frequency response curve consists of a series of regularly spaced notches, giving the appearance of a comb. Yes, just like a hair comb. 

When this happens, you end up with certain cancellations and amplifications in the audio spectrum, as some frequencies are amplified and others attenuated. Some frequencies may even be cancelled out all-together. The resulting sound that you are left with is a bit metallic sounding and very unpleasing. Voices in particular sound harsh and sharp due to significant parts of their fundamental frequency range being absent.

Comb filters become particularly disturbing when they change over time, as it can happen when the musician, instrument or microphone moves during the performance or recording process. 

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