Greetings
I mostly record around our property in southern Vermont, except when
I go to the Bay of Fundy in August. I have noticed for some time that
there is a constant low frequency noise in all of my recordings. I
never investigated it until last night when I woke up and could hear
a loud hum at around 90 Hz. That turns out to probably be low
frequency tinnitus because it is not present in the test recordings I
made in the night, while I could "hear" it plainly. But in the
process of investigating that hum I was reminded of this other noise
because it is so prominent in the spectra.
I made multiple recordings in various rooms of the house and the
cellar and porch today, and outside pointing the microphone in four
directions. The noise is there in all recordings, loudest outside,
quietest in the cellar.
The frequency is low, around 45 Hz with clear harmonics. The
intensity is low, around 5 dB SPL inside and about 15 dB SPL outside.
Those numbers are very, very approximate. I do not have a SPL meter
that reads that low, so I extrapolated based on the levels in the wav
file. Also, in order to hear it at all and have the harmonics show up
in a spectrum image, I had to apply a High Cut filter above 100Hz.
Otherwise it is buried in mic noise and whatever else.
It's not a problem, I'm just curious what it is in the environment
that is producing this sound. Is this normal background noise? We
live in a small valley between two modest ridges. The sound seems to
be louder by a few dB when the microphone is pointing south, down the
valley. I wonder if it is an acoustic feature of the valley. My next
experiment will be to get out of this valley and see if I still
record this rumble.
Any thoughts?
John
John Crockett
Let us live in harmony with Earth
And all creatures
That our lives may be a blessing
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