"Radium" wrote in message
oups.com...
Hi:

I like using variable-density analog B&W negative film
optical tracks
for audio. The audio characteristics of the film make my
mouth-water.
Yes, for some wierd reason, the film's audio makes me
hungry.

Audio signal, in the form of light changing its intensity
in a
analogous manner to the sound, is shined onto a negative
film. The film
is developed and playback is accomplished by shining light
of a
constant intensity onto the developed film. As the light
goes through
the film, the patterns on the film will change the
intensity of the
light that is received by a photoelectric cell. The change
in light
intensity results in a changing electric current which is
sent into an
amplifier and then to a loudspeaker.

http://www.mtsu.edu/~smpte/twenties.html

"The Tri Ergon Process uses a technology known as variable
density,
which differed from a later process known as variable
area. The Tri
Ergon process had a pattented flywheel mechanism on a
sprocket which
prevented variations in film speed. This flywheel helped
prevent
distortion of the audio. Tri Ergon relied on the use of a
photo-electric cell to transduce mechanicalsound
vibrations into
electrical waveforms and then convert the electrical
waveforms into
light waves. These light waves could then be optically
recorded onto
the edge of the film through a photographic process.
Another
photo-electric cell could then be used to tranduce the
waveform on the
film into an electrical waveform during projection. This
waveform
could then be amplified and played to the audience in the
Theater. The
Fox Film Corporation acquired the rights to the Tri Ergon
technology in
1927. "

The ERPI system, Fox-Case's Movietone, and De Forest's
Phonofilm use
variable-density recording film audio



Regards,

Radium

If you are really interested in this there is a perfectly
enormous amount of material in the _Journal of the Society
of Motion Picture Engineers_, later the _Journal of Motion
Picture and Television Engineers_. Variable density
recording was very widely used for Hollywood motion pictures
from the beginning of sound until it was eventually
supplanted by variable area (more accurately variable width)
tracks around the 1960's.
Because they owned nearly all of the patents covering
electronic amplifiction and vacuum tubes Western Electric
and RCA were able to suppress competitors in recording
apparatus so that by about 1930 Fox-Case Movietone and other
systems dissapeared. The last sound-on-disk was released
about 1933 but had been pretty much replaced by sound on
film. Both Fox and Warner Brothers became Western Electric
licensees, Warner later changed to RCA who had a more
sensible royalty charge.
Until the late 1930's Western Electric made variable
density recorders and RCA always made variable area. Both
companies found methods to use their modulators to produce
both kinds of tracks. I've heard intermixed tracks of both
kinds made by Western Electric recorders and have been
unable to tell them apart.
Good photographic recording is excellent but one has a
hard time finding examples of older tracks these days
because so many original release prints are no longer in
projectable (or playable) condition and later reprints,
restorations, etc., are not printed correctly so the sound
can be quite distorted.
From about 1940 both 20th Century-Fox and M-G-M were
using double width, push-pull density tracks for original
recording. This equipment was made by Western Electric and
was flat from 40 to 10,000 hz, had under 1% distortion, and
about a 70db signal to noise ratio. Release tracks were
never this good but the best of them are quite impressive.
Photographically, sound recording has many special
problems not encountered in pictorial photography. For one
thing it is necessary to compensate for image spread in
printing, especially in width recording. A good method of
determining the correct recorder and printer exposures was
not developed until the late 1930's. There is also the
problem of reciprocity failure in density recording using
the ribbon light valve (Western Electric) because of the
very short exposure times at high frequencies.
Once magnetic recording was sufficiently perfected all
studios switched to it for original recording. Not much
photographic recording for other than release prints was
done after about 1951.
At any rate, we are right back to sound-on-disk again
albeit digital disks.
The original message was sent to several news groups, I
am confining my reply to rec.photo.darkroom. This does have
some on topic content because good photographic sound
recording is vitally dependant on proper printing and
processing.


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Richard Knoppow
Los Angeles, CA, USA