From: Eldad Tsabary (tazberry_docs@yahoo.ca)
Date: Sat Mar 12 2011 - 14:56:14 EST
Hello all,
While looking with students on methods of increasing dynamic range of
pieces, we EQed individual tracks that have no business in the lower
range with a high pass filter (2nd order) at 120 Hz. The idea was that
getting rid of rumble from all of the tracks (except bass-range tracks)
can both clean the overall mix and reduce measured amplitude peaks of
individual tracks without losing actual loudness (thus allowing to bring
the entire mix to a louder RMS).
This, to my surprise, didn't work at all. In all cases I tried so far,
instead of reducing the dB measurement, the signal after processing had
a higher dB peak measurement (I used non-realtime EQ in order to use
higher quality DSP but also to be able to measure the overall signal).
It doesn't make much sense to me because the HPF is supposedly just a
passive filter. Using HPF in Pro Tool 8's EQ on a drum overhead track
reduced the overall audible loudness and got rid of the bassy sound of
the kick. It sounded softer but strangely it measured as 2 dB higher
than the original signal.
I tried the scientific EQ in Adobe Audition, which is supposedly a well
designed low phase filter (same setting - 2nd order, 120 Hz), and it
resulted in only a 0.5 dB increase - but still an increase.
Does anyone know of this? Anyone has knowledge or ideas about the
possible cause of this?
The several reasons that I have been thinking of are:
1. quantization error - though it seemed to me waaay too much of an
increase
2. some individual transients that were somehow corrupted in the process
3. dc offset
4. phase issue
Any insights would be helpful
Thanks
Eldad
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