Variable Density Greyscale Film for audio

Discussion in 'Darkroom Developing and Printing' started by Radium, Sep 21, 2006.

  1. Radium

    Radium Guest


    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.

    "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


    Radium, Sep 21, 2006
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  2. 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 This does have
    some on topic content because good photographic sound
    recording is vitally dependant on proper printing and
    Richard Knoppow, Sep 23, 2006
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  3. Radium

    Radium Guest

    Are these variable-density or variable-area?
    Radium, Sep 25, 2006
  4. Variable density. M-G-M used variable density
    exclusively, Fox used both. I don't know if Fox used any
    area tracks for original recording. Warner Brothers and some
    others used push-pull Class-A variable area tracks for some
    original recording. Republic Pictures used Class-B double
    width variable area, AFAIK, that was unique. The late Waddy
    Watson, who became head of Universal's sound department
    worked for Republic in the old days and told me that they
    sometimes spent all night lining up the recording system. In
    theory Class-B push pull has virtually no background noise
    but the ballance has to be perfect or the distortion becomes
    serious and is of a very annoying kind. I have also seen
    samples of push-pull tracks from Paramount but I am not sure
    how widely they were used there. Paramount was one of the
    first studios to switch to magnetic recording for original
    recording purposes thanks to Loren Ryder. I think they
    changed over about 1951 but were making some magnetic tracks
    as early as 1948 on home made equipment. John Aalberg, who
    was once head of RKO-Radio sound told me that they had
    experimented with push-pull but could not hear enough
    difference to use it routinely. BTW, don't judge RKO sound
    quality by the television reprints, the sound is not printed
    correctly and results in a very spitty donald duck quality.
    Some current Turner Classic Movies prints are very good
    IMO Fox and M-G-M were right at the top for both quality
    of sound and skill in re-recording although all the majors
    did very good work.
    The M-G-M recording system is described in detail in the
    Journal of the Motion Picture Engineers for sometime in 1938
    or 1939, I don't have the citation at hand but I think the
    article was written by John K. Hillyard.
    For much more on various film recording systems, in
    cluding the three chanel stereo system used by Bell Labs,
    see: _Elements of Sound Recording_ John G. Frayne and Halley
    Wolfe, 1949, John Wiley and Sons, Inc. See also: _Motion
    Picture Sound Engineering_ Various authors, New York, 1938,
    D. Van Nostrand Co.
    Both are a bit rare but larger libraries should be able
    to get them. Dr. John Frayne was a poineer in sound
    recording who worked for Bell Labs and was materially
    responsible for the development of the modern stereo disc
    cutter. The second book was developed from a course in
    motion picture sound recording given by the Research Council
    of the Academy of Motion Picture Arts and Sciences. While
    both are very old much of the information is still valid and
    they do describe the equipment in use from about the mid
    1930's to the 1950's.
    This has been long an area of special intrest to me so
    your original post, although off topic, pricked up my
    Richard Knoppow, Sep 26, 2006
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