On 2023-03-08, Eero Aro wrote:
Chris Woolf wrote:
Anyone any ideas how one could provide an audio horizon that could be a
mimic of the gyro artificial horizon?
A vague thought, that applies only to a small amount of surround sound
recordings. [...]
I also maybe should say, as a vague thought, many of the early and still
extant aeronatical radio thingies do just this. The nondirectional
beacons spell out their identities in slow Morse code. Typical
instrument landing systems, even if they're decoded digitally by now,
originally were designed to be listened to by ear. Both laterally and
vertically; if you listen to them by ear, you actually *can* still fly
by it.
I do mostly nature recordings and record also in urban areas, where
the distant traffic hum is always present.
Ever heard what happens when you get an inversion layer, so that there's
suddenly a vertical component to the soundfield? Because it does happen,
from time to time.
Around here in Finland, it often happens in the summer over our many
lakes. The inversion layer over the lake beams sound for
miles/kilometres on end, and since it does so, you'll have a stark
Z-component upon reception, even if you sent it as a purely cylindrical
wave. (Rarely do you do that even, since pantophonic isn't right
cylindrical to begin with. And then, no antenna or microphone array
really does either right pantophony or periphony.)
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?
Here in the north the distant traffic noise is also different in the
winter and in the summer. We use studded tyres in the cars and they
cause more high frequencies in the noise than unstudded tyres.
Sounds pretty much like what our tyres here in Finland do, in noise.
Though, is it really the same?
Another thing that changes the sound scene in the winter is snow, it
makes the general acoustics more dry and then it is easier to detect
the direction of single sound sources.
I'd argue snow attenuates single sound sources, and so makes easier to
multilaterate them from a distance. But if you try to measure the sound
source which is a tyre pressing on snow, it's almost im*possibly*
nonlinear of a source.
It really is. Just do a high order Volterra series minded correlation
between what a driven tyre does, and how it sounds. Especially on show,
ice, and gravelled now. It's almost stupidly nonlinear, and how it
skids, can take almost half a minute to die down. The analysis of such a
thing is even as of now almost impossible to do, optimally.
The problem is that a constant wide spectrum noise (the traffic hum)
is more difficult to localize than signals that have transient
content.
True. If you want to localize the stuff. But then at the same time, you
can localize noise better than any impulse, by averaging it in time.
Here we even have information theoretical optimality theorems to bear.
Having said that, we _do_ localize an above flying jetplane, although
it produces a noise type sound. We know from experience, that an
aeroplane almost always is flying above us.
Yes. We have our neural circuits, and then many of the deep learning
circuits of today do the precice same thing.
However, the reason we (and then the deep learning AI circuit) is not
just about a "noise type sound". What happens is that our hearing does
wideband, even Doppler analysis. We just hear, via all of that noise,
how things move, and even parts of what they *are*, as *initial emitters
of sound*. We're just that good, as the best of mammals.
But are we actively aware of the fact, that distant traffic hum
appears as a zone above the horizon.
Are we, though? I tend to be aware of such things, but most of the time
I still can't tend to anything horizontal. And then, when I *can*,
suddenly it's the vertical axis I can't tend to.
Also, it would be somewhat strange to put artificially some kind of
signal "beacons" at the horizon level around the listener, because
they aren't part of the actual recording.
In the radio amateur circuit this has been done, in so many ways. In
fact in right "beacons", as on WSPR and such. There *is* the idea of QRP
radiofinding, as a sport, and who knows whatelse.
--
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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