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Re: Making a parabola

Subject: Re: Making a parabola
From: "Scott Fraser" scottbfraser
Date: Fri Sep 21, 2012 8:12 am ((PDT))
<< I=B9m wondering how you=B9d do this ? Why wouldn=B9t you roll off the ba=
ss post-recording instead? I really don=B9t see how you could simply put  b=
ack bass that was never recorded.>>

To further elaborate on David's & Klas' responses, wind rumble on a mic is =
a very high amplitude signal. If you adjust the record gain so that the win=
d rumble doesn't distort, your desired sounds are recorded at a needlessly =
very low level, at a point where preamp & converter noise start interfering=
 with the sound. If you don't adjust level for the rumble you get preamp ov=
erload & converter clipping which add upper harmonics throughout the spectr=
um, resulting in a ruined recording. I.e. it's not just bass which can be s=
imply high pass filtered out at this point. So we use bass cuts (high pass =
filters) in order to preserve headroom in the original recording chain, hea=
droom which can't be reconstituted in post production.
Additionally, a high pass filter does not eliminate bass frequencies. It at=
tenuates them. So bass is still recorded through a high pass filter, but at=
 a lower level, & this is what David refers to by putting back bass in post=
. It's there & can boosted by the same amount as the bass cut on the mic/pr=
eamp/mixer in order to restore natural lows, if needed. Generally, nature h=
as rather little energy in the lowest octave of human hearing most of the t=
ime, except for thunder, waterfalls, waves & a few other geologic events. S=
o rolling off lows primarily serves to attenuate human vehicular noise. Win=
d rumble goes all the way down to DC & the gentle 6dB/octave curve David me=
ntions, even if at 50Hz is enough to eliminate the most pernicious effects =
of rumble while still allowing a reasonable sense of low frequency reality =
to be recorded.
So, a long answer to your query, but the short version is that we have to s=
tart with the best possible recording of the original event, & not plan on =
fixing problems later, since many of the problems relating to wind actually=
 can't be fixed adequately in post.

Scott Fraser








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