I have a .wav file which came off of a cd with a scratch, so there is a periodic "clicking" of about 6 Hz. I was playing around with trying to squash the clicking by taking FFT and filtering the range around this frequency, but with no success. I tried smoothing the low end of the FFT spectrum, but it didn't change anything. Then I tried zeroing this part of the spectrum up to higher and higher indices, but it still wouldn't kill the click. Eventually it started to attenuate the entire signal, but the click was still there, and perhaps even more prominent than before (relative to the rest of the signal). Why is this the case?
My first speculation is that the click is somehow not quite steady enough to be localized in a single region of the spectrum. Can anyone confirm this hypothesis or else explain the true source of the issue? Also, is there a better means of eliminating the click?