In signal processing, a comb filter adds a delayed version of a signal to itself, causing constructive and destructive interference. The frequency response of a comb filter consists of a series of regularly spaced spikes, giving the appearance of a comb.
In acoustics, comb filtering can arise in some unwanted ways. For instance, when two loudspeakers are playing the same signal at different distances from the listener, there is a comb filtering effect on the signal. In any enclosed space, listeners hear a mixture of direct sound and reflected sound. Because the reflected sound takes a longer path, it constitutes a delayed version of the direct sound and a comb filter is created where the two combine at the listener.
Audio effects, including echo, flanging, and digital waveguide synthesis. For instance, if the delay is set to a few milliseconds, a comb filter can be used to model the effect of acoustic standing waves in a cylindrical cavity or in a vibrating string.
Basically comb filtering is the enemy when it comes to audio (unless it’s an effect). The frequency at which comb filtering begins is based on the time difference between two or more signals. Comb filtering doesn’t exist where signals are in sync. As two or more signals (electronic or acoustic) are mixed together out of sync (time), they begin to interact in good and bad ways. The frequency at which this tug of war begins is based on how far out of sync (time) those signals are. The further out of sync (time) they are the lower the comb filtering begins. With the wrong amount of time offset between signals you can literally ruin the sound your PA system reproduces. Here are two examples of comb filtering and what to look for in order to recognize when you’ve got comb filtering. How do you eliminate or at least manage comb filtering? That answer is a long one but the idea is to time align signals that will interact with each other. Sounds easy huh?
Comb filtering is not your friend!
Think of comb filtering as audio poison. Don’t drink it!!!