ABSTRACT
The summation of audio signals can be acoustic or electrical: acoustically, sound sources in a room recorded at position; or electrically, microphones connected to a mixer, combined and routed to one output. The filtering function that arises when a signal adds to itself after being delayed is called a comb filtering. The resulting frequency response looks like a comb, hence the name. The comb filter function is rarely intentional, but it is heard all the time in sound productions, where it can arise both acoustically and electrically. The listening position can be either in the direct sound field or the diffuse sound field. In the direct sound field, there is only one sound direction from each source. This direct field exists either in the open, in a reflection-free room, or close to the speakers. The distance from the speakers where the direct sound field and the diffuse sound field are equally large is called the critical distance.
