I agree with Kevin about the abundance of VLF, even in remote places.
I think sounds from great distance are mostly under 40Hz. It seems
the LF "roll-off" filter often gets enlisted when the garbage is
overwhelming and residing as high as 250Hz, even 500Hz. Those
frequencies in the lower mid-range in my perception. LF "roll-off"
is not really the best filter to use for this and since the tonal
balance can best be adjusted in post, I haven't engaged those
filters in years. [Tape was a little different than digital media--
the HF gets eaten up more with tape.] If there's a predominance of LF
in the subject like a garbage truck, try getting the mic closer to
where the higher frequencies are being created. This will add tonal
breadth. A LF filter will not.
The last time we discussed the topic it was under "speakers for
editing" and I do think that targeting your monitoring in "LF
management," as the pros like to say, is something to consider.
If I'm following umashankar correctly, the only way one could
practice the theory of "flat frequencies response" --that is-- not
correcting for volume and monitoring Hz balances difference-- would
be to match the sound playback level of the original sounds.
This is doable for sounds above 50 SPL but not when trying to image
low level sounds like acoustic space or the "ambience" of quiet
natural settings. We've all noticed that we need to increase the
playback volume of such recordings a great deal, probably 12-30 dB
louder than we use for music to achieve levels that are 6-10 dB
louder than background sound level of the playback space.
So, for speakers, unless the "nature" you are recording is quite
loud, "correction" and aesthetic judgement is very likely to be
involved. As Kevin says, changes are often necessary to be more
consistent with what was heard.
Quieter spaces also tend to have very low dynamic range and subtle
tonal differences. This really changes the way mixes work on us and
sound "right." One shouldn't need much LF < 125Hz filtering for
quiet location ambience unless you are _really_ cranking up the
volume. Yes, there is a very large percentage of VLF energy in the
background sounds of such recordings, but, as umashankar points out,
our ears are inherently insensitive to these lowest pitches.
Try using a few bands of parametric EQ on "culprit" peaks between 125
and 500 Hz to lessen (not remove) the presence of the offensive
sounds and let the LF be. You might find the result to feel more
accurate and easier on the ears.
Always EQ at the same level you will play the material back. To
significantly improve upon these results when working with broad
bandwidth, low dynamic material, duplicate the monitoring and the
room used (or send everyone a pair of the really great headphones you
used). Rob D.
At 8:21 PM -0700 4/4/09, umashankar wrote:
>before you vote for or against low frequency filtering, consider this.
>
>in many situations, the low frequencies are not intrusive when you
>are there, but they become so in the recording.
>
>this is almost always because we listen at much higher volume than
>real life levels. the ear's sensitivity to low frequencies is very
>low at low levels. when you boost recorded levels (during the
>recording, during processing, or in playback) low frequencies you
>could not hear earlier become audible.
>
>it is up to you to decide which is more acceptable, a theoretically
>flat frequencies response, or a correction to accommodate the
>elevated playback.
>
>umashankar
>
> i have published my poems. you can read (or buy) at
><http://stores.lulu.com/umashankar>http://stores.lulu.com/umashankar
>
>________________________________
>From: Steve Pelikan <<pelikan%40math.uc.edu>>
>To:
><naturerecordists%40yahoogroups.com>=
m
>Sent: Sunday, April 5, 2009 8:18:44 AM
>Subject: [Nature Recordists] New thread: Low Hz filtering
>
>Friends:
>
>This is a subject that has been touched on often but never discussed
>explicitly (in my memory) and that is low frequency filtering of
>"ambient" recordings.
>
>I've started to get interested in making stereo recordings of entire
>"sound scapes" --- meaning whatever is there --- and am in the
>process of deciding how I'll treat such recordings --- so I'd
>appreciate other people's opinions.
>
>My understanding of the 'elevated' low Hz 'noise' in most settings
>is that most of it (that I experience) is low Hz man made noise that
>carries a long way because of its wave length ( Hi Hz interacts with
>"stuff" and disappears rather quickly with distance).
>
>When I'm out to document things I record w/o filters. This is in the
>eastern US where there's lots of manmade sound. When I want
>something that "sounds nice" I use (or process with) a low Hz filter
>(10 dB to 20 db/ octave starting at 160 -600 Hz, say).
>
>I've heard "professional" recording with _nothing_ below 200 Hz
>and they sound goofy to me. I've been tempted to filter recordings
>more heavily but realized that it (for eg) might eliminate low Hz
>thumps of a woodpecker on a rotten stump.
>
>How do you al think about this issue? What do you do?
>
>Sometimes I put on a low Hz filter so I can set the overall record
>level higher (buy headroom by eliminating something under 100 Hz).
>Sometimes I really miss the low Hz stuff.
>
>Sorry for this elementary and ambiguous posting/question but it
>think there is room for some discussion on this topic. In the end we
>all need to listen carefully and do what sounds best for a
>particular setting, but I'm curious if there is a general
>understanding about this matter.
>
>Cheers! (and Good Recording! which others have used and seems a
>superior salutation)
>
>Steve P
>
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