I agree with David,
a sharp cut-off sounds unnatural; I prefer a gentle roll-off
that attenuates but not completely removes, background noise. Excessively
cleaned recordings does not feel natural.
Gianni
2015-05-02 20:42 GMT+02:00 [naturerecordists] <
>:
>
>
> > I forgot that it was relatively close to a major highway.
>
> Tom,
>
> A study showed that birds sing louder with a high background noise.
>
> > I seemed to have problems with highway noise even when I had the
> microphones pointing away from the highway.
>
> Gunmics have a lot of side lobes at different frequencies and the "gun
> effect" only really works at the higher frequencies when the wavelength i=
s
> comparable to the director tube. At 5KHz, the wavelength is around 7cms.
>
> At lower frequencies they have a cardioid response with some really bad
> rear
> lobes. The best rejection is often around 90 deg and in real life you can
> get as much as 20db less sensitivity off axis.
>
> Now for the real story. The solid angles including up and down are also
> picking up general noise but all this solid angle is less sensitive with =
a
> gunmic. Sometimes you can also baffle this noise with a car or your body
> or
> a tree and as I suggested, try putting the rig on the ground. On grass yo=
u
> can often hear a drop in the BG hubbub. Don't ask me for the theory but i=
t
> works. I taught this trick to a generation of assistant Sound Recordists
>
> > I was able to get a lot of the highway noise out with the =E2=80=9Chigh=
pass
> filter=E2=80=9D in Audacity.
>
> I make no apologies for using filters and my favourite is a gentle LF
> roll-off. Many bass cuts have a sharp kink to 6db per octave but mine
> doesn't. Any kink in a response produces a resonance of some sort and thi=
s
> can often be heard if you listen for it.
>
> You can construct and edit your own filters easily in Audacity using a
> text
> editor. First find the file:
> <EQCurves.xml>
> Copy this to a safe place so you can put it back if you goof up. Here are
> my
> default bass roll-off curves (HPF) Don't be put off by it going up to
> 800HZ.
> It starts to bite below about 200Hz.
>
> You can use these filters twice or more times and undo them using the
> invert
> function.
>
> <curve name=3D"HPF800-1-2-3">
> <point f=3D"20.000000000000" d=3D"-12.700000000000"/>
> <point f=3D"200.000000000000" d=3D"-3.000000000000"/>
> <point f=3D"400.000000000000" d=3D"-1.000000000000"/>
> <point f=3D"800.000000000000" d=3D"0.000000000000"/>
> <point f=3D"22049.000000000000" d=3D"0.000000000000"/>
> </curve>
> <curve name=3D"HPF800-2-4-6default">
> <point f=3D"20.000000000000" d=3D"-26.000000000000"/>
> <point f=3D"200.000000000000" d=3D"-6.000000000000"/>
> <point f=3D"400.000000000000" d=3D"-2.000000000000"/>
> <point f=3D"800.000000000000" d=3D"0.000000000000"/>
> <point f=3D"22049.000000000000" d=3D"0.000000000000"/>
> </curve>
> <curve name=3D"HPF800-3-6-9">
> <point f=3D"26.000000000000" d=3D"-35.000000000000"/>
> <point f=3D"200.000000000000" d=3D"-9.000000000000"/>
> <point f=3D"400.000000000000" d=3D"-3.000000000000"/>
> <point f=3D"800.000000000000" d=3D"0.000000000000"/>
> <point f=3D"22049.000000000011" d=3D"0.000000000000"/>
> </curve>
>
> Have fun.
>
> David Brinicombe
>
>
>
--
Centro Interdisciplinare di Bioacustica e Ricerche Ambientali
Universit=C3=A0 degli Studi di Pavia
Via Taramelli 24, 27100 Pavia
http://www.unipv.it/cibra
http://mammiferimarini.unipv.it
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