Friday, May 11, 2012

On The Edges Of A Dawn Chorus



1. Noises in a Landscape


On the edges of a dawn chorus
the leading edge or the trailing edge
just before all the birds start singing
or right after all the birds finish
the sounds throughout a landscape are noise
and who can say what’s making the noise
although if we know birds make birdsong
and we all know what a bird looks like
then we can imagine what makes noise
since noise is sound nothing like birdsong
whatever it is that makes the noise
probably is nothing like the birds.



2. Three Graphs


She said, “I’m going to show you three graphs.
This first one represents the amplitudes
of all the average background noises
recorded before and after the birds
sing their dawn chorus. Look at the levels.
Across the entire audible spectrum
the amplitudes seem to change randomly
and math tools confirm that it is random.
This second graph is the time period
of the dawn chorus. Notice there are spikes
within well-defined frequency ranges
and while the spikes themselves appear random
you can see what appear to be patterns
in where groups of the spikes begin and end.
Those are birdsongs. We can characterize
the lengths of the groups and the silences
mathematically and it’s non-random.
I have a third graph. On this I subtract
all the amplitudes of the birdsong spikes
from the period of the dawn chorus
except during the time of the silence.
That is, I subtract the birdsong except
from the time-slices where there’s no birdsong.
And then I subtract background amplitudes
from that. So there’s no birdsong, no background.
If there’s no birdsong and there’s no background
then what do you think the third graph will show?”

He said, “I would expect it to be blank.”

She said, “Look at this third graph. There are spikes
in those time-slices that should be silent
and the spikes are higher in amplitude
than background noise. What do you think that is?”

He said, “They must just be math artifacts
from all your processing algorithms.
Or recording artifacts introduced
because microphones are non-linear
in their frequency response and change too
as the ambient temperature changes.”

She smiled and said, “Do I look like someone
who can’t sort out artifact from signal?”

He frowned and said, “What do you think it is?”

She said, “I think there’s something making noise
that’s not there before the dawn chorus starts
and isn’t there when the dawn chorus ends.”



3. Noises in a Landscape (Reprise)


On the edges of a dawn chorus
the leading edge or the trailing edge
just before all the birds start singing
or right after all the birds finish
the sounds throughout a landscape are noise
and who can say what’s making the noise
although if we know birds make birdsong
and we all know what a bird looks like
then we can imagine what makes noise
since noise is sound nothing like birdsong
whatever it is that makes the noise
probably is nothing like the birds
and imagination can conjure
so many shapes of so many things
that if there were a way to see them
should a scientist or someone else
do their science or do something else
to make these things visible and real?























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