Calculating Comb Filter Frequencies; Comb Filter Amplitude - SABINE Power-Q Operating Information Manual

The frequencies of the reinforcements and cancellations depend on the delay time (the time
difference between the arrival time of the original signal and the delayed signal). The frequency of
the first cancellation occurs at 1/(2t) Hz, where t = the delay time in seconds. The cancellations
are separated by (1/ t) Hz. Fig. 11 shows how the comb filters change with the delay time.
If the original signal and the delayed signal are the same amplitude, the reinforced frequencies
4
increase in amplitude by 6 dB, while the out-of-phase frequencies cancel completely to - dB.
Comb filters cause a lot of problems. The frequencies that are reinforced are prone to excite
feedback, while the out-of-phase cancellations make the program sound thin and over equalized.
Try this simple experiment to hear what comb filters do to your sound.