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Industrial One · Guest

On Jul 13, 3:05 pm, dpierce.cartchunk....@gmail.com wrote:
[quote]On Jul 12, 10:58 am, Industrial One <industrial_...@hotmail.com
wrote:

On Jul 10, 6:56 pm, dpierce.cartchunk....@gmail.com wrote:
[SNIP]

Very eloquent explanation. However, anything spinning over 24 fps will
appear spinning backwards to the human eye anyway, cuz we don>t
perceive movement any more precise than that, just like no
neurotypical dude can hear over 20 KHz.

No, we do NOT perceive them as "spinning backwards,"
we perceive them as blurred.
[/quote]
Depends how fast they spin. If enough to capture part of the frame
when you focus your eyes on the oscillation rather than on a fixed
spot at the wheel then it may appear to spin backwards, at least with
me. I believe the limit is... yeah, 'bout 25 fps. If spinning faster,
'course it>ll appeared blurred.

[quote]There>s another phenomenon called "aperture error" or
"aperture filtering" which, in the case of the eye, is due to
the so-called "persistance of vision." It, in effect, "smears"
the continuous input of images.

Now, interestingly enough, as a complete analog
of my wagon-wheel gadanken, how might we prevent
the aliasing of the wagon wheel motion, given that we>re
limited to, oh, 25 frames per second?

Well, you "low-pass filter" the wagon wheel, i.e.,
blur its motion, before sampling, so that nothing
makes it through to the "sampler (the shutter"
any faster than 1/2 the shutter or frame rate
That>s a little tough to actually accomplish in the
real world. "Aperture filtering" is one way to get
part of the way there: you make your shutter speed
as long as possible. IN the simplest case, it can>t
be any longer than 1/25 of a second, which would
have the effect of blurring things enough such that
things goign faster that 1/25 of a second are blurred
wnough that there>s nothuing left to alias, but doesn>t
solve the problem of what happens between < 12.5
and 25/second.
[/quote]
Isn>t it already blurred before sampling? No camera captures a
perfectly still image. All got expose times of at least 1/30th a
second, 1/40th 1/50th whatever so if you took a picture of a wheel
spinning faster than that, it>ll already be blurred.

[quote]One might imaging a somewhat more sophisticated'
movie camera that exposes each frame for, say 1/12
second, but interleaves frames such that halway
through frame 1, it starts exposing frames to, and
frame 1 continues unitl halway through frame 2, at
which point frame 3 starts getting esposed, etc.
[/quote]
You got it.

On Jul 13, 4:24 pm, UnsteadyKen <unsteady...@gmail.com> wrote:
[quote]Industrial One said:

Very eloquent explanation. However, anything spinning over 24 fps will
appear spinning backwards to the human eye anyway, cuz we don>t
perceive movement any more precise than that, just like no
neurotypical dude can hear over 20 KHz.

We may not "hear" it but the brain registers the presence of
frequencies considerably higher than 20Khz:http://jn.physiology.org/cgi/content/full/83/6/3548
[/quote]
Yeah, it>s called binaural beats, you don>t hear it, you feel it.. I
once had the priviledge of getting a friend>s high-class electronic
playground all to myself for a while, I had this bigass subwoofer
output about 5 Hz and amplified the volume to hardcore maximum. I
didn>t hear shit but I swear to god I FELT like shit, like a complete
drop to an emo kid>s state -- suicide (I swear to god.) It>s real hurl-
inducing too I should note. I wonder what happens at say 500 dB, 1000.
Can some mind-control weapon be built on this idea? Drop an emo bomb
on Iran, say?

I got a shitload of binaural beat files that advertise mind-altering
effects, I only tried S-Angel2 so far (valium) which actually worked.
I gotta try the heroin and microdots ones sometime to see if they
work.

[quote]Similarly we are aware of visual frequencies over 24FPS. Most of us
have come across a faulty fluorescent tube or a computer screen with
a low 50-60hz refresh rate which we sense as an almost subliminal
flicker.

--
Ken
[/quote]
You>re imagining it, take your pills boi.

Richard Crowley · Guest

<dpierce.cartchunk.org@gmail.com> wrote ...
[quote]No, we do NOT perceive them as "spinning backwards,"
we perceive them as blurred.
[/quote]
Then you>ve never done the experiment youself.
Actually try it and get back to us.

UnsteadyKen · Guest

Industrial One said:

[quote]Very eloquent explanation. However, anything spinning over 24 fps will
appear spinning backwards to the human eye anyway, cuz we don>t
perceive movement any more precise than that, just like no
neurotypical dude can hear over 20 KHz.
[/quote]
We may not "hear" it but the brain registers the presence of
frequencies considerably higher than 20Khz:
http://jn.physiology.org/cgi/content/full/83/6/3548

Similarly we are aware of visual frequencies over 24FPS. Most of us
have come across a faulty fluorescent tube or a computer screen with
a low 50-60hz refresh rate which we sense as an almost subliminal
flicker.

--
Ken

UnsteadyKen · Guest

Industrial One said:

[quote]Yeah, it>s called binaural beats, you don>t hear it, you feel it..
[/quote]
It>s called infra sound. The US, UK and Russian military investigated
its use as a weapon years ago. It works but can>t be projected so it
wasn>t practical. The same effect is can cause problems in large
buildings with lift shafts which act as Helmholtz resonators.
It appears to be a very old technique:
http://www.orkneyjar.com/history/tombs/tombacoustics.htm

[quote]once had the priviledge of getting a friend>s high-class electronic
playground all to myself for a while, I had this bigass subwoofer
output about 5 Hz and amplified the volume to hardcore maximum. I
didn>t hear shit but I swear to god I FELT like shit, like a complete
drop to an emo kid>s state -- suicide (I swear to god.) It>s real hurl-
inducing too I should note. I wonder what happens at say 500 dB, 1000.
Can some mind-control weapon be built on this idea?
Yes it>scalled shell shock.[/quote]

[quote]Drop an emo bomb
on Iran, say?
[/quote]
No I don>t say. You can practise on Calgary if you like.

--
Ken

isw · Guest

In article <B-6dnV_Ax7E6FufVnZ2dnUVZ_uLinZ2d@posted.pcez>,
"Richard Crowley" <rcrowley@xp7rt.net> wrote:

[quote]dpierce.cartchunk.org@gmail.com> wrote ...
No, we do NOT perceive them as "spinning backwards,"
we perceive them as blurred.

Then you>ve never done the experiment youself.
Actually try it and get back to us.
[/quote]
Are you confusing what happens in the movies ( a sampled data situation
if there ever was one), with what happens in "real life"?

Isaac

Mr.T · Guest

"Industrial One" <industrial_one@hotmail.com> wrote in message
news:f11fa4d4-4eee-437d-90f5-005e4b0a8a11@f36g2000hsa.googlegroups.com...
[quote]I wonder what happens at say 500 dB, 1000.
[/quote]
If you mean dB SPL, that is a physical impossibility at normal atmospheric
pressures. From memory a swing to complete vacuum, gives around 180dB SPL,
but of course an asymmetrical swing to greater than twice air pressure can
increase things a bit.

MrT.

Guest · Posted: Mon Jul 14, 2008 12:18 pm Post subject: Re: Frequency/Sample rate

On Jul 14, 1:04 am, "Mr.T" <MrT@home> wrote:
[quote]"Industrial One" <industrial_...@hotmail.com> wrote in message

news:f11fa4d4-4eee-437d-90f5-005e4b0a8a11@f36g2000hsa.googlegroups.com...

I wonder what happens at say 500 dB, 1000.

If you mean dB SPL, that is a physical impossibility at normal
atmospheric pressures. From memory a swing to complete
vacuum, gives around 180dB SPL,
[/quote]
Actually, this is a common misconception. The low
pressure swing has no need to go to a vacuum for
symmetry. It merely has to match, factor-wise, the
positive swing.

For example, consider a symmetrical pressure swing
where it swings a factor of 2 about atmospheric pressure:
that means at its highest, the pressue is twice that of
atmosphere, and at its loweest,. it>s hald that of
atmosphere.

New, where the problem comes is the fact that such
large swings cause nonlinearities because the ideal
gas equation likely no longer holds. Consider:

PV = n R T

which, for small swings in atmospheric pressure
typical with "survivable" (!) sound pressure levels
holds true. THere are some underlyingh assumpitons,
e.g., that based as it is on the kinetic theory of gases,
that the medium consist of essentially point sized
particles that interact through perfectly elastic collisions,
and that the properties of these particles are independent
of temperature, and that, as far as sound is concerned.

These are all true fro small deltas of P, V, and, especially T,
but is increasingly less true as the magnitude of things
start to increase. For example, air molecules behave like
point paritcles at low sound levels, but no so at high
levels. You encounter abrupt discontinuities as energies
start to reach those necessary to effect diassociation of
air molecules, changes in the linearity as more energy is
put into non-translational kinietic ebergy modes, i.e.,
expanding of the molecule, and so on.

But as far as "hitting" the vacuum at the bottom of the
swing: nope. That>s not an issue.

Consider one more gedanken: imagine a speaker set in
the wall of a seled room. One could determine that for
all frequecnies whose wavelength is large compared to
the dimensions of the room, the sound pressure level
in the room is a function of the excursion of that speaker.
In other words, assuming we adopt the convention
that excursion of the speaker>s diaphragm into the room
is "positive, then since the volume in the room is an
inverse function of the excursion of the diaphragm, and
that pressure is an inverse function volume, then pressure
is a function of diaphragmn excursion.

(for the nit-pickers, whether we are ssuming adiabatic
or isothermal conditions is relatively unimportant at
this point since the end conclusion remains essentially
the same in principle, differing only in magnitude)

Now, let>s take you assertion:

"a swing to complete vacuum, gives around
"180dB SPL,

Ignoring whether it>s 180 dB or 210 dB or a bazillion
dB, how far sdoes that diaphragm have to move in the
nnegative direction to create a pure vacuum in that room?
(hint, it has to move an infinitie distance).

More importantly, if you want to skip a WHOLE bunch
of physics, how much energy would it take to create that
vacuum? (hint: inifinite).

All this because:

PV = nRt

or,

P = nRT/V

Thus, the relation is a reciprocal one, and when
you plot the relation, you end up with a function whose
graph is asymtotic to the X and Y axes and can never
equal 0.

Guest · Posted: Mon Jul 14, 2008 5:59 pm Post subject: Re: Frequency/Sample rate

On Jul 13, 7:11 pm, "Richard Crowley" <rcrow...@xp7rt.net> wrote:
[quote]dpierce.cartchunk....@gmail.com> wrote ...

No, we do NOT perceive them as "spinning backwards,"
we perceive them as blurred.

Then you>ve never done the experiment youself.
Actually try it and get back to us.
[/quote]
Actually, I have. Any number of times.

Could you elcidtae the conditions under which you
saw the phenomenon?

Guest · Posted: Mon Jul 14, 2008 6:03 pm Post subject: Re: Frequency/Sample rate

On Jul 13, 7:25 pm, Industrial One <industrial_...@hotmail.com> wrote:
[quote]On Jul 13, 3:05 pm, dpierce.cartchunk....@gmail.com wrote:
Well, you "low-pass filter" the wagon wheel, i.e.,
blur its motion, before sampling, so that nothing
makes it through to the "sampler (the shutter"
any faster than 1/2 the shutter or frame rate
That>s a little tough to actually accomplish in the
real world. "Aperture filtering" is one way to get
part of the way there: you make your shutter speed
as long as possible. IN the simplest case, it can>t
be any longer than 1/25 of a second, which would
have the effect of blurring things enough such that
things goign faster that 1/25 of a second are blurred
wnough that there>s nothuing left to alias, but doesn>t
solve the problem of what happens between < 12.5
and 25/second.

Isn>t it already blurred before sampling? No camera captures a
perfectly still image. All got expose times of at least 1/30th a
second, 1/40th 1/50th whatever so if you took a picture of a wheel
spinning faster than that, it>ll already be blurred.
[/quote]
Professional movia and video cameras allow you
to adjust shutter speed independently of frame
rate, up to a limit. For example, with a rate of 25 FPS,
you could set the shutter speed to anything from, say,
1/1000 second to about 1/30 second in the normal
1-stop increments. This was to allow you to be able
to say, have a shallow depth of field (wide aperture)
under birght light without having to switch to a slower
film.

Guest · Posted: Mon Jul 14, 2008 6:07 pm Post subject: Re: Frequency/Sample rate

On Jul 11, 4:20 pm, Willem <wil...@stack.nl> wrote:
[quote]dpierce.cartchunk....@gmail.com wrote:

) On Jul 11, 8:24 am, zekfr...@zekfrivolous.com (GregS) wrote:
)> Not any waveform. Just a sinewave.
)
) No, it>s ANY waveform whose components are within
) the Nyquist bandwidth (i.e., < 1/2 sample rate) ANY
) waveform whatsoever.

And what are those components ? Sine waves, right ?
[/quote]
Read it again: he said:

"Not any waveform, Just >a< sinewave"

"Just a sine wave," which seems to definitely say
"one" sinewave.

Guest · Posted: Mon Jul 14, 2008 6:12 pm Post subject: Re: Frequency/Sample rate

On Jul 11, 8:24 am, zekfr...@zekfrivolous.com (GregS) wrote:
[quote]Its interesting aliasing can be seen with nothing to do with time,
but its still a sample, such as with viewing lines through various
filters.
[/quote]
It has to do with "sampling," and as such has the
property whether one is sampling in the time domain
or one is sampling in the spatial domain. It could happen
in ANY data domain: take a bunch of social security
number gathered at random. Sort them numerically.
Pick out every 5, and try to tell us that most social security
numbers end in 2 or 7. or 4 and 9, or some such. Aliasing.

ChrisCoaster · Guest

On Jul 14, 1:59 pm, dpierce.cartchunk....@gmail.com wrote:
[quote]On Jul 13, 7:11 pm, "Richard Crowley" <rcrow...@xp7rt.net> wrote:

dpierce.cartchunk....@gmail.com> wrote ...

No, we do NOT perceive them as "spinning backwards,"
we perceive them as blurred.

Then you>ve never done the experiment youself.
Actually try it and get back to us.

Actually, I have. Any number of times.

Could you elcidtae the conditions under which you
saw the phenomenon?
___________________________[/quote]
Sure! I>ll elcidtae one instance - actually many - when I>ve seen the
spinning backward phenonemon:

Whenever a pilot throttles up a prop-driven plane or turns the engines
off. For a brief few seconds the props appear to change directions as
the props wind down to a stand still.

Ever elcidtae that? If you haven>t then you are either blind or from
a planet where propellers are not used for air transport.

-CC

ChrisCoaster · Guest

On Jul 15, 4:22 am, "Mr.T" <MrT@home> wrote:
. My only point was
[quote]that *I think* 500dB or 1000dB SPL is still *theoretically* impossible in
air.

MrT.- Hide quoted text -

- Show quoted text -
____________________[/quote]
Ask anyone who has been within 5-miles of a 1950s atomic bomb test.

-CC

Mr.T · Guest

<dpierce.cartchunk.org@gmail.com> wrote in message
news:024a5a6a-b1c0-488d-b0cd-b00ab5ef2e69@w7g2000hsa.googlegroups.com...
[quote]On Jul 14, 1:04 am, "Mr.T" <MrT@home> wrote:
"Industrial One" <industrial_...@hotmail.com> wrote in message
news:f11fa4d4-4eee-437d-90f5-005e4b0a8a11@f36g2000hsa.googlegroups.com...

I wonder what happens at say 500 dB, 1000.

If you mean dB SPL, that is a physical impossibility at normal
atmospheric pressures. From memory a swing to complete
vacuum, gives around 180dB SPL,

Actually, this is a common misconception. The low
pressure swing has no need to go to a vacuum for
symmetry. It merely has to match, factor-wise, the
positive swing.

For example, consider a symmetrical pressure swing
where it swings a factor of 2 about atmospheric pressure:
that means at its highest, the pressue is twice that of
atmosphere, and at its loweest,. it>s hald that of
atmosphere.

New, where the problem comes is the fact that such
large swings cause nonlinearities because the ideal
gas equation likely no longer holds. Consider:

PV = n R T

which, for small swings in atmospheric pressure
typical with "survivable" (!) sound pressure levels
holds true. THere are some underlyingh assumpitons,
e.g., that based as it is on the kinetic theory of gases,
that the medium consist of essentially point sized
particles that interact through perfectly elastic collisions,
and that the properties of these particles are independent
of temperature, and that, as far as sound is concerned.

These are all true fro small deltas of P, V, and, especially T,
but is increasingly less true as the magnitude of things
start to increase. For example, air molecules behave like
point paritcles at low sound levels, but no so at high
levels. You encounter abrupt discontinuities as energies
start to reach those necessary to effect diassociation of
air molecules, changes in the linearity as more energy is
put into non-translational kinietic ebergy modes, i.e.,
expanding of the molecule, and so on.

But as far as "hitting" the vacuum at the bottom of the
swing: nope. That>s not an issue.

Consider one more gedanken: imagine a speaker set in
the wall of a seled room. One could determine that for
all frequecnies whose wavelength is large compared to
the dimensions of the room, the sound pressure level
in the room is a function of the excursion of that speaker.
In other words, assuming we adopt the convention
that excursion of the speaker>s diaphragm into the room
is "positive, then since the volume in the room is an
inverse function of the excursion of the diaphragm, and
that pressure is an inverse function volume, then pressure
is a function of diaphragmn excursion.

(for the nit-pickers, whether we are ssuming adiabatic
or isothermal conditions is relatively unimportant at
this point since the end conclusion remains essentially
the same in principle, differing only in magnitude)

Now, let>s take you assertion:

"a swing to complete vacuum, gives around
"180dB SPL,

Ignoring whether it>s 180 dB or 210 dB or a bazillion
dB, how far sdoes that diaphragm have to move in the
nnegative direction to create a pure vacuum in that room?
(hint, it has to move an infinitie distance).

More importantly, if you want to skip a WHOLE bunch
of physics, how much energy would it take to create that
vacuum? (hint: inifinite).

All this because:

PV = nRt

or,

P = nRT/V

Thus, the relation is a reciprocal one, and when
you plot the relation, you end up with a function whose
graph is asymtotic to the X and Y axes and can never
equal 0.
[/quote]

Thanks for the comprehensive analysis Dick, I am certainly no expert on this
topic. (yes that>s obvious :-)
However I wasn>t quite so stupid as to think a vacuum was possible from any
sound driver, or indeed a "perfect vacuum" even in space. My only point was
that *I think* 500dB or 1000dB SPL is still *theoretically* impossible in
air.

So is there in fact a *theoretical limit* (ignoring physical implementation,
and non linearities), and if so do you know what it is?
Or am I completely off base here?

MrT.

Phil Carmody · Guest

"Richard Crowley" <rcrowley@xp7rt.net> writes:
[quote]"Mr.T" wrote ...
"ChrisCoaster" wrote ...
My only point was
that *I think* 500dB or 1000dB SPL is still *theoretically* impossible
in
air.
____________________
Ask anyone who has been within 5-miles of a 1950s atomic bomb test.

Ask them what exactly? Whether they have a better clue what 500dB-
1000dB SPL means than you?
No one could have first hand experience and still be alive, assuming it is
even possible.

"Around 260 personnel were present, none closer than 5.6 miles (9 km)."
http://en.wikipedia.org/wiki/Trinity_test
[/quote]
And as this is cross-posted to comp.compression, I can
only assume that you audio dudes want to know how to compress
5.6 miles to less than 5 miles?

Phil
--
Dear aunt, let>s set so double the killer delete select all.
-- Microsoft voice recognition live demonstration


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