Sound Theory -

A Comb Filter

When discussing audio and signal processing, a Filter is a device that removes unwanted frequencies from a given signal. 

There are many different types of filters and we highlighted some common types of filters in a previous blog post

What we didn't talk about was a special kind of filter called a comb filter. 

A Comb Filter adds a delayed version of the signal to itself, creating constructive and destructive interference.

Comb filtering creates peaks and troughs in frequency response that are caused when signals that are identical but have phase differences are summed. When seen on a frequency response it resembles the image of a comb. 

Comb Filtering

Advantages / Disadvantages 

This can be disadvantageous for mixing and sometimes happens with phase issues when using overhead drum microphones or when there are phase issues with two or more microphones in use.

It can be advantageous for electronic music and you can make some awesome gritty noises that are unattainable with other methods of filtering the given sound source.