I wrote:
>>> We positioned the array in a large open field about 200 yards from a
>>> very active waterfowl pond, with mics oriented toward the pond.
>>> Later, playing back the center
>>> stereo pair, I noticed there was almost nothing there above 8khz,
>>> unlike other recordings I made that same day with that same pair.
Dan Dugan asked:
>> To what are you attributing this phenomenon? An interference
>> cancellation from the ground reflection? That could make a "hole" in
>> the frequency response if all the sources were in the same horizontal
>> plane, but I wouldn't expect a low-pass effect, and my gut feeling is
>> that it wouldn't happen that high in the spectrum. Maybe an
>> atmospheric lensing effect?
>>
>> Were the outrigger channels at the same height?
>>
>> Also, the waterfowl I'm thinking of don't have much high frequency
>> stuff, at least not compared with forest and bush critters. You would
>> hear hf in the spashing, tho.
Rich Peet answered:
> Well, I attribute it to a few things and will have to return Curt to
> that prairie to convince him.
>
> This is a prairie of Switch Grass with no reflective objects for more
> than a mile in any direction. THe Switch Grass in itself is sound
> absorbant. This is a good chunk of land with infrequent man made
> noise for over 4 miles. What I need to show Curt again is that this is
> how an absorbant quiet natural space sounds and that it in itself is
> now a rare sound field.
Rich is exactly right. It's a rare soundscape, particularly beautiful
at this time of year. And there's nothing "wrong" with the recording we
made. The huge area of low prairie vegetation and the long distance
between the mics and the primary sound sources -- mostly ducks and
geese -- would naturally yield a recording with little high frequency
content. And at the distance we were from the pond, much of the HF from
the splashing would be dissipated too.
I was trying to make an entirely different point, and did it very
poorly. I was reflecting on the vast difference between a) "being
there" and b) playing back a recording of it at a later time. I'll
admit that I managed to enjoy a lengthy experience in that setting
without stopping to critically analyze what I was hearing. But that's
the point, and the reason I called this "Ears and Mics." While I was
there with Rich, my ears and brain were taking it all in and accepting
it for what it was -- hearing, compensating and interpreting without
conscious critical analysis. It wasn't until later that afternoon, back
home in my studio, with only the audio illusion the microphones
captured, that I noticed the lack of HF content. I immediately
understood why, but was mostly impressed that I had not noticed it
until then.
I'll stop now before I dig myself any deeper into this hole I'm in...
Curt Olson
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