At 12:05 PM -0800 1/6/08, Dan Dugan wrote:
>I heard a low-frequency roar above me and to the left. I was puzzled
>by that, as I was in the
>tallest trees. I wondered if it could be the surf from the ocean--
>it's a usually inaudible background in Muir Woods from around two
>turns about 3.3 miles down the canyon, but one night when the surf
>was up it was a lot louder.
My first impression was that of a distant surf because of the
sustained quality. Seems like the energy from the wind in the trees
would bury such a distant source, but the left weighting might
support the surf explanation.
>
>In the clip the low rumble is particularly audible to me between
>gusts 2-3 and 3-4, and leftish.
Pertaining to the left heavy distant sound, yes, its more apparent
after gusts 2 and 3.
>
>I don't think you can have standing waves in a V-shaped canyon.
I played around a little with mixing in multiple sine tones with the
material between 1:56 to 2:04 and there do seem to be some low,
stand-out frequencies lending a very deep sustained sense of "force."
These tones seem louder here than after gusts 2 and 3. I'm not sure
how they are being generated, but there's clearly enough natural
energy at work to produce them. I also notice left-right movement in
the higher registers/harmonics (300-900Hz?) of the "roars" in this
section which seem to be adding to the impression of scale. Its Rob D.
>
>-Dan
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