Chel van Gennip wrote:
In a discussion about SACD quality here, the discussion came on absorption
of sound in air. We found some references for this absorbtion that might
be interesting in general:
http://www.sensorsmag.com/articles/0...299/main.shtml I thin the
http://www.ktu.lt/ultra/journal/pdf_...adisauskas.pdf

I used the sensorsmag data to create a table of sound absorption for the
audible range: http://www.serg.vangennip.com/absorption.pdf

It is indeed more than you expect. For a living room situation I see about
3 db for 20 kHz at 4m. For a concert hall situation I see 20dB loss for
20kHz at 28m. I am afraid there are no fast transients or extremely high
frequencies for sound in a real life concert hall.

From real life we know high frequencies are absorbed, just look at the
sound of a thunderstorm passing by, the sound of fireworks nearby and high
in the air, the sound distribution on open air festivals. It is however
more than you expect.

Well - IIRC my first audio book bascially said something about
the "roll off point" of sound being absorbed in air is around 6kHz.
Where that roll off point is may be a bit more important as a practical
matter than an exact calculation of how far down 20Khz is at 28 meters
I think; if the diffuse sound is greater than the direct sound where
you place your mic no amount of high end boost is really going to
"equalize" the difference much and bring the source closer, no? But in
the direct field you can compensate for air absorbtion somewhat with
eq, and get a bit more "reach" I think.

For a TV application example if a lavalier mic is a bit too far
from someone's mouth than I'd prefer, I might tweak up 5-6kHz a bit to
compensate for the distance, and maybe add a bit of low end as well to
compensate for the loss of any desirable "proximity effect" bass you
get when the mic is closer to an anchor's mouth.

Will Miho
NY Music and TV/Audio for Video/Live Sound Guy
"The large print giveth and the small print taketh away..." Tom Waits