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Bill Pragnell wrote:
> Nah, hollywood only tends to do it in 2 dimensions,
There was a video showing the real-time shockwaves going thru the Iceland
volcano ash as it was coming out of the cone.
--
Darren New, San Diego CA, USA (PST)
Linux: Now bringing the quality and usability of
open source desktop apps to your personal electronics.
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On 4/29/2010 8:13 AM, clipka wrote:
> It's being done, not only for IR, but also for radio/microwave.
I'm supposing that's what the radio telescope images some from....
> Thermal IR cameras are pretty well established as equipment for e.g.
> police helicopters to search for or track people (particularly at night).
Yep. But those cameras are very expensive pieces of equipment, and have
to be specially cooled in order to work properly.
> Sound "images" are common for sonar systems. And ultrasound imaging
> devices, for that matter.
Well, that and Doppler radar (used for weather) also shows an image of a
radio wave of sorts. (A very similar concept, actually)
I was thinking more along the lines of a "CCD" for radio type device,
though. I think the radio telescopes generally examine a small are of
the sky for a certain frequency, then composite the information to build
a picture.
--
~Mike
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On 4/29/2010 9:27 AM, Bill Pragnell wrote:
>
> Do you think it only *looks* 'shopped, or do think it actually *is* 'shopped?
> I thought it looked as one would expect it to, personally.
>
Watch Mythbusters enough and you'll see one ...
--
~Mike
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On 4/29/2010 9:33 AM, Invisible wrote:
>> I thought it looked as one would expect it to, personally.
>
> I'm rather surprised that it's a real effect. I thought it only happens
> in Hollywood action films. But, apparently, it's real. Even if it does
> look hard to believe...
What always surprising to me is how a real detonation is so
underwhelming compared to a Hollywood detonation. No fireball, just a
loud report, the shockwave and a dust cloud.
--
~Mike
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Mike Raiford wrote:
> What always surprising to me is how a real detonation is so
> underwhelming compared to a Hollywood detonation. No fireball, just a
> loud report, the shockwave and a dust cloud.
I think that depends on whether it's a controlled explosion or not. If
you're intentionally blowing up a building, you don't *want* much more than
that. If the propane tank catches on fire, yeah, it's probably gonna be louder.
--
Darren New, San Diego CA, USA (PST)
Linux: Now bringing the quality and usability of
open source desktop apps to your personal electronics.
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Darren New <dne### [at] san rrcom> wrote:
> Mike Raiford wrote:
> > What always surprising to me is how a real detonation is so
> > underwhelming compared to a Hollywood detonation. No fireball, just a
> > loud report, the shockwave and a dust cloud.
>
> I think that depends on whether it's a controlled explosion or not. If
> you're intentionally blowing up a building, you don't *want* much more than
> that. If the propane tank catches on fire, yeah, it's probably gonna be louder.
Has anyone seen The Kingdom? There's a large carbomb towards the end that was
actually done for real with the explosives they said were used in the script...
looked terrifying. And not at all typical hollywood :)
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> Sure, it's not expensive for suitably large definition of "expensive". ;-)
Usually "expensive" means expensive for the apparent/usual value. eg a new
car for 5000 pounds is not expensive, but a phone for 1000 pounds is
expensive.
Not for a specialist camera.
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>> Sure, it's not expensive for suitably large definition of "expensive".
>> ;-)
>
> Usually "expensive" means expensive for the apparent/usual value. eg a
> new car for 5000 pounds is not expensive, but a phone for 1000 pounds is
> expensive.
>
>
> Not for a specialist camera.
What I'm saying is that it's far more expensive than anything *I* could
ever afford.
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Mike Raiford wrote:
> It's amazing when you look at how your auditory system works. Your brain
> essentially gets the Fourier transform of what you're listening to.
Be careful with that...
Audio systems generally represent sound in the time domain. The Fourier
transform moves data from the time domain to the frequency domain. But
humans don't hear sound in the frequency domain; they hear it in a
*combination* of both domains - i.e., as a spectrum that changes over time.
You can take a 5-minute song and take the Fourier transform of it, and
that will only tell you what combination of [fifty zillion] sine waves
you need to add together to get back the same waveform. That's not how a
human would perceive it; they hear notes and beats and things - sounds
*changing* over time, but one static combination of frequencies.
It turns out this is one of the most tricky things in DSP. Working with
signals that have a meaning in *both* domains...
(You might think, for example, that you could just snip your 5-minute
song into, say, 50 ms chunks and take the Fourier transform of each
chunk. Alas, snipping it up introduces phantom frequencies that aren't
really there.)
I've spent a significant amount of time trying to come up with some
mathematics for analysing sound the way that the human auditry system
does... So far, nothing works.
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> (You might think, for example, that you could just snip your 5-minute song
> into, say, 50 ms chunks and take the Fourier transform of each chunk.
> Alas, snipping it up introduces phantom frequencies that aren't really
> there.)
Use something other than a rectangular window function then, that helps with
the phantom frequencies.
> I've spent a significant amount of time trying to come up with some
> mathematics for analysing sound the way that the human auditry system
> does... So far, nothing works.
If you don't need it in realtime then just run a band-pass filter over the
whole song at varying frequencies, you can then read off the amplitude at
any frequency at any time during the song.
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