Interesting Glitch with High Pass

[mikeebb]

I went searching and didn't see anything like this - but then maybe not the right search terms. Anyway:

I have a file that has been normalized to -0.5 db. Works fine. But there's a little rumble, so I tried using a high pass filter, trying both 18 & 24 db/oct slopes. Worked on the rumble, but it punched the level up at least a db resulting in clips. So ... why?

Other than the obvious - do the high pass before normalizing - any idea what's going on and what I can do about it? I don't see anything in the filter control box that can adjust levels so I assumed that x db in would be about the same (or less, if I succeed in removing something) out. Since I usually work on music I prefer to use the traditional filters rather than brick wall.

Thanks.

Mike

[Craig Maier]

The IIR high pass filter will exhibit a few dB of gain at the corner frequency when using 2nd, 3rd or 4th order settings (filter peaking - filter transient response). Try using a 1st order setting. To compensate for the mild slop produced by 1st order (6dB/Octave) just set the corner frequency higher than you otherwise would.

Craig