On 2023-03-10, Eero Aro wrote:
The hum can be heard as a horizontal noise somewhere in the
distance.
Now this is rather interesting. "The hum?" Tell me more, what is this
"hum" all about?
I didn't mean "The Hum". I meant the noise that comes from the
engines, motors and tyres of the vechicles and from the ventilation
and air conditioning fans of the buildings.
That's really, *truly* difficult to deal with. Filter out. Because we
don't have an overarching mathematical theory of such mixed noises.
It's also a mixed bag. We do have an extended theory of how to deal with
that in case it happens to mix to something like Gaussian noise, or the
its extension towards stochastic processes of the same kind.
But then it often does not. Impulse noise is a particular problem,
especially in the radio bands I'm trying to learn about, year on end.
The statistics, both in time and over frequency, any transform domain
known, on that sort of thing, are just horrible. Nobody really has a
coherent theory on which to work with, there.
Let's not go to the Hum. please.
Let's not. Just saying, the whole idea of "The Global Hum" really just
comes from our lack of understanding of how to understand wave
mechanics. More in radio than audio, but still in both. (And then fuck
the dynamics of plasma in the near-earth conditions. Or stellar winds.
Solar coronal heating after a sunspot. That shit is just *wild*, and
*wildly* under-/misunderstood. Just, no, I don't get it what it does to
my audio setup, and nobody else does either.)
Sounds pretty much like what our tyres here in Finland do, in noise.
Sampo, I am in Finland, not far from you.
Yet do you understand how tires fold into the discussion. Because they
do. They do *all* sort of nonlinear, resonant things. And so does the
road. Especially our winter tires do, at the higher frequencies.
Did you know they nowadays build the studs in our winter tires and their
toroidally varying tension *by design* in a pattern which evokes
multiple nonharmonically related, complex vibration modes over the tire?
In order to drive off water, and regain traction.
This is actually a thing. Your tires are manufactured to do internal
acoustics.
Well, the distant traffic noise comes from the tyres pressing against
asphalt, partly or totally covered with ice. On snow, that noise is
pretty quiet.
It actually is not, because snow crystals being crushed down at speed is
kind of loud. Part of the reason we salt the road is also about taking
down the loudness.
Obviously, there's a lot more to be reckoned with here. Say, skidding on
an icy road. You might think it's just a one time thing. But on a busy
highway, this too happens at about ten second intervals per kilometre,
the sound power put out is extremely high, and averaged over a stretch
of a usually rather straight section of a highway, the scaling law of
how this all radiates outwards tends to go a bit down. It slowly starts
to go towards coherence, so that it radiates further, more efficiently.
--
Sampo Syreeni, aka decoy - de...@iki.fi, http://decoy.iki.fi/front
+358-40-3751464, 025E D175 ABE5 027C 9494 EEB0 E090 8BA9 0509 85C2
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