At 1:00 PM -0500 12/4/06, Barry Blesser wrote:
>The discussion actually has several additional layers of issues.
>
>First, there is no question that an elevated microphone will produce a com=
b
>filter frequency response
Close to flat ground, a good percentage of the sounds from great
distance come in parallel to the ground. The mass of the plant and
other materials tend to absorb more of the high frequencies so the
impression created is not unlike that of lost high frequencies due to
distance and is different from secondary reflections/comb filtering.
> because the direct signal will merge with a
>delayed version that bounces from the ground. One observes the same issue
>with office speakerphones where the microphone is as close to the table to=
p
>as possible, thereby avoiding the delayed reflection from the table top.
>
>Second, the question of what constitute "natural" pops up. As adults
>standing in the field, our ears are some 5 feed above ground and we too he=
ar
>the comb filter response, but we call that natural because we expect to he=
ar
>it. However, doing a recording is different from human listening, because =
in
>the first case, the sound source and the listener are in one shared
>environment. When reproducing a recording, however, the listening
>environment may be stereo loudspeakers in a laboratory, headphones with so=
me
>binaural processing, or whatever. There are therefore two sets of acoustic=
s:
>the source space and the listening space.
>
>The same issue appears when trying to record music. Even though the
>applications and goals are different, the discussion about musical space i=
n
>my book, Spaces Speak, is directly relevant to all forms of recording. One
>must carefully analyze the choices in the context of the specific goals.
In terms of the sound waves/science, correct, but not to a great
extent-- in terms of practical choices like where to set what mics
etc. I wish there were more sills that overlapped. A recordist's
familiarity with the surfaces and dimensions of spaces/locations is
pretty important.
It does help me to analyze a natural space in terms of its
"enclosure" properties even the dimensions are very large. Its also
very important to incorporate the behaviors of sounds entering the
space for a great distance and how these phenomena interact. I spend
time searching for nodes that some concert hall recordists could
predict, but not that many.
The micing/equipment skills are different enough from many types of
recording that we have learned to make a number of distinctions--
particularly those of us who record ambience in very quiet natural
settings. Here are a few that come quickly to mind:
1) Recording in quiet, natural locations can demand much higher gain
than those typically used by studio or concert hall engineers. This
seems to make the flaws in the technologies as a whole and in
specific pieces of equipment and short-comings of "accepted"
practices more apparent.
2) We often try to judge reverberant field performance of mics--
recording situations when the mic to sound source distance is 30
yards or much further. There's not a rich vocabulary to fall back on
when we do this. It would, for example, make a great deal of sense
to many of us if the industry developed standards for reverberant
field mic performance.
3) When we discuss spatial imaging in recordings, and we try to
compare actual recordings when possible, we know there is both
localization and depth and that there are many, many variables to
account for-- the largest being the playback situation as you discern.
4) And,...because distinctions in such recordings are often hard to
make, discussions of acoustics can wear out the delete key for some
readers. Rob D.
>
>At least this is my two-cent view of the discussion.
>
>Regards,
>Barry Blesser
>
>
>
> -----Original Message-----
> From:
> Behalf Of Steve Pelikan
> Sent: Sunday, December 03, 2006 11:04 PM
> To:
> Subject: Re: [Nature Recordists] Re: microphone stands in the field
>
>
>
> This is a question I've worried about a fair bit.
>
> Is this because, by putting the mic well above the ground you're making
>the sound reflected off the ground follow such a longer path that (inverse
>square law) it has much less energy than the direct path?
>
> This I understand, but the then same or better effect would be attained=
by
>putting the microphone directly at ground level, since then there'd be no
>reflections off the ground?
>
> Or are you referring to some aspect of sound propagation through the
>vegetation near ground level, in which case how does the optimal height
>depend on the habitat? (I know and agree with you that the best answer is
>"listen and you'll know" but could you offer some guidelines as starting
>points?)
>
> Thanks!
>
> Steve P
--
Rob Danielson
Peck School of the Arts
University of Wisconsin-Milwaukee
http://www.uwm.edu/~type/audio-art-tech-gallery/
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