--- In "hartogj" <>
wrote:
>
> Hi Jim,
> We are often reminded that sound attenuation with distance
approximates a reduction of 6dB for each doubling of distance. However,
as you and Klas point out, the actual attenuation over distance is
highly frequency dependent. This suggests the 6db rule would only be
accurate at one specific frequency, and any general rule would need to
include an approximate adjustment for frequency.
> Does that make any sense,if so do you know of a common use equation
that includes a frequency adjustment?
>
> John Hartog
> www.rockscallop.org
The perception of distance from a sound source is not only created by
the reduction of sound pressure and modifications in frequency that the
air applies to it, but also by acoustic effects that the
environment's 'body' (a valley hillside, the ground, etc) produce.
There are delay/echo and reverb effects which add a lot to the sensation
that 'something is closer or farther away'.
Producing a formula for such variations in frequency 'loss' and its
relation to air density, humidity and movement is only possible to be
achieved =96 to a 'perfect state' =96 in vitro. I'm far from saying
here that it is an irrelevant field of study though, besides the fact
I'm pretty sure that there are greatly better people in this list to
discuss on that matter. But I believe I could add a bit to the subject.
As I work with sound post-production for audiovisuals, I should say that
in the process of designing and mixing the sound of a film/video we
often face the task of creating the sensation of spaciousness/distance.
The biggest challenge is to make it sound 'natural', obviously. And what
we mostly tweak with to get the 'effect' is equalization PLUS
delay/echo+reverb, as without the latter, one cannot produce the
'distance effect'.
The variations in frequency loss regarding distance are not only
restricted to the higher frequencies either, but a lot has to do with
the lower range too =96 which can be easily perceived by talking
closer and farther from a mic. But to create such sensation, the most
difficult part is that the losses vary all over the frequency range,
varying their 'proportions' as the source moves from 'far to farther'.
(What I'm saying here is that it doesn't sound linear to my ears).
A little off topic extra 'stuff':
'Distance' is not easy to be created in post if the scene is outdoors.
In some way it's such a hard job to accomplish in a higher level that
sound mixer Owe Svensson is loudly acclaimed by his achievements in the
film Sacrifice, by Tarkovski. Creating indoor acoustic effects is an art
but well documented and it has a lot of tools to work with, but in
Svensson's case he did it for outdoors =96 which is what we're
interested in here =96, a much more difficult task, a completely
different 'league'. The first sequence on Tarkoviski's film is an
outstanding example of Svensson's artistic/technical assets, as he
creates in studio =96 in vitro =96 the 'perfect' sensation of a
sound source moving closer and closer. And again, the plus consists in
the fact that the whole scene takes place in the open field.
Luiz
PS: Here is a link to an interview with Mr. Svensson:
http://filmsound.org/owesvensson/
>
> --- In Jim Morgan fundador@ wrote:
> >
> > Thank you Klas for the additional information. Your paper provides
much more
> > detailed information and many members would benefit by reading it.
> >
> > Jim
> >
> > On Sun, May 22, 2011 at 3:42 PM, Klas Strandberg telinga@ wrote:
> >
> > >
> > >
> > > Thanks Jim!
> > >
> > > Let me contribute. This was written in... 1991?
> > >
> > > http://www.telinga.com/attach.htm
> > >
> > > Klas
> > >
> > >
> > > At 21:20 2011-05-22, you wrote:
> > > >As most of us know sound amplitude and frequency are attenuated
as the
> > > >distance to the sound source increases.
> > > >
> > > >
> > > >This effect heard from recordings made of various sounds at
different
> > > >distances are often noticeable but difficult to clearly hear.
> > > >
> > > >
> > > >Also recordings made with parabolas amplify the higher
frequencies more
> > > than
> > > >the low frequencies thereby making the recorded sound seem closer
than it
> > > >actually is.
> > > >
> > > >
> > > >The following test of sound vs. distance is an example of sound
amplitude
> > > >and frequency attenuation.
> > > >
> > > >
> > > >Here is a description of the test which is the recorded sound of
a kitchen
> > > >timer bell at 15, 30, 60, 90, 150, 300 feet. Note the significant
> > > >attenuation of the higher frequencies that increase with
distance.
> > > >
> > > >
> > > >Recording at:
> > > http://soundcloud.com/fundador/bell-test-15-30-60-90-150-300
> > > >
> > > >
> > > >Recorded with a 23 inch Telinga Twin science parabolic microphone
in an
> > > open
> > > >field with no obstructions between the bell and microphone.
> > > >
> > > >
> > > >Best regards,
> > > >
> > > >
> > > >Jim Morgan
> > > >
> > > >Prescott, AZ USA
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >------------------------------------
> > > >
> > > >"While a picture is worth a thousand words, a
> > > >sound is worth a thousand pictures." R. Murray Schafer via Bernie
Krause.
> > > >
> > > >Yahoo! Groups Links
> > > >
> > > >
> > > >
> > > Telinga Microphones, Botarbo,
> > > S-748 96 Tobo, Sweden.
> > > Phone & fax int + 295 310 01
> > > email: telinga@
> > > website: www.telinga.com
> > >
> > >
> > >
> > >
> > >
> >
> >
> >
>
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