Interesting pic !

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Hi to all,


ever wondered how Dolby Digital 5.1 sound is  ACTUALLY  carried by a 35mm
cinema film  ?

Turns out the 320 kbit/s DD data stream is encoded onto squares optical
grids of about 60 x 60 bits & very cunningly fitted in * between*  the
sprocket holes  !!

http://upload.wikimedia.org/wikipedia/commons/1/1d/35mm_film_audio_macro.jpg

The embedded Dolby logo is cute dontcha think  ?

A tiny CCD camera in the projector captures each 2.4mm square image, 96 of
them per second, so it can be processed into 5 channels of audio.

The other tracks you see are Sony SDDS,  L/R stereo analogue and timing
pulses for  DTS so the CD can be synched with the movie.

Such a multi-format movie can be shown by any cinema in the world and exact
copies are made by ordinary, chemical film processing.

Betcha you  ALL  knew that already    ....




.......    Phil



Re: Interesting pic !


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    Interesting and educational. There's lots more photos and info at
http://www.maniacpony.pwp.blueyonder.co.uk/onscreen/sound.htm

Bob


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"Bob Parker"
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**  I would still like to know how the CCD camera reliably acquires 3500
bits of data from 96 tiny squares every second.

Does the film come to a halt 96 times per second to give the camera a
stationary image to snap  ?

Or,  is the CCD exposure time so short that relative motion is effectively
frozen ?

Maybe clever spinning optics are used to make the image appear stationary to
the camera  ?




........    Phil



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Perhaps the exposure time is short, but to make it even finer, a flash
is fired 96 times a second. This technique is used in high speed
photography.

Cheers,
Nicholas Sherlock

--
http://www.sherlocksoftware.org

Re: Interesting pic !



"Nicholas Sherlock"

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**  I suppose a high brightness LED could be pulsed at 96 Hz continuously.

The optical data bits are approx 1/800 of an inch square and the film speed
is about 18 inches per second,  ie it moves the width of a data bit in
1/15,000 of a second.

The light pulse would need to last 20 uS at most to stop action !!



.......   Phil






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    I found a projector setup procedure
(http://www.film-tech.com/warehouse/manuals/CENMR3.pdf ) which seems to
indicate that the Dolby digital pickup is illuminated by continuous LED
light and is positioned where the film's moving at a constant speed.
    Apparently the CCD is functioning as a very fast electronic shutter.

Bob

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That makes sense, they need a constant speed portion for the analogue pickup
anyway.


--

Bye.
   Jasen

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I thought that happened with all film projectors, using, for example, the
Maltese cross mechanism: <http://en.wikipedia.org/wiki/Maltese_Cross_mechanism .
But IIRC on normal film, the audio is displaced by a few frames and recovered
from continuously moving film.

Clifford Heath.

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    One of those articles mentions the digital area of the film being
scanned 24 frames away from the gate, where it's moving continuously not
being stopped for projection of each frame.
    Maybe they pulse high intensity LEDs for a couple of microseconds to
grab each optical digital block?
    There's probably info on some of the professional sites... I'll have
a look when I get time.

Bob

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"Clifford Heath"
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 **  Did you even read your own URL  ?

   Says the film stops 24 times per second -   not 96.



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**  Bit hard to recover any analogue audio from a stationary film.



......  Phil







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The film runs at 24fps but there are 4 sprocket holes per frame
(
http://upload.wikimedia.org/wikipedia/en/c/cc/Anamorphic-digital_sound.jpg)

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"ER"
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  **  Is this profound   -   or just silly ?





.....   Phil





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Neither really, just pointing out that although the film runs at 24fps
there are 4 sprocket holes per frame with 4 gaps filled with DD5.1 data
hence the 96 times per second figure for the number of images camera takes.

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" Exasperating Ratbag "



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  **   What crapology !

Worse than merely silly  -   it is completely  STUPID.

Another MORON who cannot read or follow a simple thread  !!


PISS  OFF     -   IDIOT   !!!





.......  Phil




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wow, whered that come from Phil?

Do you suffer from tourettes or something?


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"Simple Simon"


 =  Another Exasperating Ratbag


    PISS  OFF     -   IDIOT   !!!





.....    Phil



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He suffers several diseases , closely akin to  tourettes but with a bad
case of a philthy past bad foot in mouth .

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Just do a Google Groups search on "Phil Allison+Tourette's Syndrome".  You'd
be surprised what you come up with.



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Your search - "Phil Allison+Tourette's Syndrome" - did not match any
documents.


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Sure you tried Google under Groups?
My search got 152 results.
http://groups.google.com.au/groups?q=Phil+Allison%2BTourette%27s+Syndrome&hl=en&ie=UTF-8&oe=UTF-8 &




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