Questions/opinions about variable-density optical audio track recording.

Discussion in 'Photography' started by Green Xenon [Radium], Apr 22, 2008.

  1. Hi:

    I am not asking homework questions. The questions are out of my interest
    in variable-density film audio.

    My favorite analog audio storage medium consist of the optical
    equivalent of magnetic tape. It is similar to the optical tracks of old
    analog B&W films -- except without the video or any images. My optical
    tape records audio optically on a tape using variable-density encoding
    [not variable-area] and is monaural. As with any photography, the tape
    must not be exposed to light before recording or development and must
    not be exposed to extraneous light [light other than the optical audio
    signal] during or before recording/development. Such exposure will
    corrupt the film. After recording. The film is developed using
    photographic chemicals. This tape is like a reel-to-reel [i.e. not a
    cassette] film using optics and chemistry instead of magnetism.

    What characteristics in the film material itself [e.g. the chemicals
    within the film, "grains", etc. etc.] determines the audio quality [e.g.
    the bandwidth, dynamic range, SNR, clipping point, treble response, etc.
    etc.] of a VD track?

    What types of audio artifacts are specifically-associated with the
    variable-density optical tracks of B&W films? What are these artifacts
    caused by?

    In magnetic audio cassette, the maximum frequency that can be recorded
    is determined by the tape speed. What determines the maximum frequency
    that can be recording onto a variable-density optical track of a B&W
    film? Is tape speed still a factor here?

    Movietone kicks photophone's @$$ because the former uses
    variable-density while the latter uses variable-area.

    I've listened to both variable-density and variable-area. I prefer the
    former over the latter.

    I don't have this analog audio storage device I described. It is
    something I would like to have but I don't. While it is possible to make
    this device, I am probably the only individual in the world who wants
    it. Nobody else cares for something like this. This is mainly because I
    am the only one who enjoys the artifacts associated with the
    variable-density audio of old B&W movies. Most everyone else prefers VA
    over VD. Not to mention, most also prefer magnetic over optical.

    The problem is my film device does not exist because there is no demand
    for it. I am the only one in the world who cares to have such a device.
    No one else has any interest in the audio quality of the old VD audio

    As for performance levels I would like the artifacts specifically
    associated with VD tracks to be clearly noticeable without ruining the
    musical quality of the audio.

    Two things I do not want -- at all -- are any clipping or aliasing. At
    the same time, I want high-quality treble. I am a fan of treble but not
    bass. I do not want there to be any distortion that specifically results
    from sounds being too loud [e.g. clipping] or from the sounds being too
    high in frequency [e.g. aliasing]. Yet I still want all treble that any
    human can hear to be encoded. The film and the rest of the equipment
    should be able to handle at least 1.5x the loudest sound a human ear can
    be exposed to without any pain or damage. Treble response should be up
    to 40 kHz or higher while the clipping point should be at 144 dB or above.

    For some reason, I find the artifacts associated with B&W VD tracks to
    be appetizing. Even I can't understand why. It's something about the
    noise/distortions [other than those caused by excess
    amplitude/frequency] in VD that I enjoy. It's like the sound of fresh
    garlic bread baking in clay oven fueled by bituminous coal. That's the
    best description I can give.

    I've listened to audio artifacts from very old B&W movies [which used
    VD]. That's where I get my opinion. I've compared it with movies that
    came out later [with VA instead of VD]. From there, is where I got my
    preference for VD over VA.


    Green Xenon [Radium], Apr 22, 2008
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  2. Green Xenon [Radium]

    Ken Hart Guest

    This is completely out of my area, but I'll throw out some ideas/concepts.

    Based on your comments, the audio output depends on the density of the
    exposed film. Film does not always have straight-line response to light.
    Additionally, the developing process may not always cause a straight-line
    density response. For example, if a particular audio tone goes from 10% to
    90% electronically, the film's response may be 10% to 50%. Additionally, the
    developement may move the film's response so that the final result might be
    30% to 100%. You have to consider the base density of the film, and the
    contrast of the film.

    As for the characteristics of the film, a finer grain film will allow a
    quicker change in density, allowing a higher frequency sound to be recorded
    for a given speed of transport.

    If I've completely missed the mark of your post, please re-read my first
    Ken Hart, Apr 22, 2008
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  3. Green Xenon [Radium]

    krishnananda Guest

    <complete snip>
    Group: sci.optics
    My optical tape records audio optically on a tape using variable-density
    8:54pm by Green Xenon [Radium]
    In variable-density optical track, what determines the frequency ...    
    Green Xenon [Radium] rec audio tech Hi: In magnetic
    Apr 18 by Green Xenon [Radium]
    Seems OT but it isn't: What determines the audio quality of a ...    
    Group: sci.chem
    Hi: Variable-density was used to record sound into the those old B&W
    films before ...
    Apr 14 by Green Xenon [Radium]
    Variable-Density Optical-Specific Analog Audio Artifacts?      
    Group: rec.arts.movies.production.sound
    The audio-artifacts specfic to an analog, VD, negative, B&W, optical
    soundtrack are a ...
    Jun 20 2007 by Radium
    Variable-Density Optical Audio Artifacts?      
    Group: rec.arts.movies.production.sound
    Hi: What audio artifacts are specific to the variable-density optical
    audio ...
    Jun 18 2007 by Radium
    Alternatives to ROM. Magnetic vs. Electric      
    Group: alt.comp.hardware.homebuilt
    Analog optical audio records and plays in the same manner as film does
    May 14 2007 by Radium
    Anyone sell string samples that sound this good?      
    I'd actually love to listen to real traditional instruments recorded on
    the variable-density optical audio tracks -- consisting of film negative
    Mar 4 2007 by Radium
    Soundcard-MIDI is *not* obsolete. It just takes an evil form.    
    Group: alt.steinberg.cubase
    Though, I gotta admit, I'd actually like to listen to an analog optical
    Mar 3 2007 by Radium
    Different Formats for Different Countries -- Variable Density ...    
    Hi: Is it true that in the days of B&W film and optical track audio ...
    Oct 12 2006 by Radium
    Analog Optical Audio in films      
    Variable density needs a very good gray scale, hence a linear transfer
    May 11 2003 by Radium
    krishnananda, Apr 22, 2008
  4. Thanks for your response.

    Ken Hart wrote:

    What do you mean by "audio tone goes from 10% to 90%"? "Goes from"??

    What determines the dynamic range in the VD track?
    Green Xenon [Radium], Apr 22, 2008
  5. Green Xenon [Radium]

    Ken Hart Guest

    I was referring to the Amplitude or volume
    I would guess the quantity of discrete density steps or shades of gray that
    the film can reproduce, the recording exposure lamp can create and the
    'pickup' system can intrepret.
    Ken Hart, Apr 22, 2008
  6. Ken Hart wrote:

    What is the finest grain that can be achieved?
    Green Xenon [Radium], Apr 22, 2008
  7. Green Xenon [Radium]

    Ken Hart Guest

    Generally speaking, the lower the film speed (the sensitivity of the film to
    light expressed as "ISO"), the finer the film's grain. Check with the
    manufacturer to determine the finest grain, usually expressed as line pairs.
    I have never used a film in the manner you are exploring, so I can't give
    exact answers; I can only answer in terms of 'pictorial' use of film.
    Ken Hart, Apr 23, 2008

  8. Can a film with a lower ISO handle a louder sound without clipping than
    a film with a higher ISO? I ask because I get the feeling that if there
    grains are finer, the film can record more levels of amplitude -- just
    like a 16-bit audio file can handle 65536 loudness levels while an 8-bit
    audio file can handle only 256 loudness levels. I could be very wrong
    though. Not sure if this is a good analogy at all.
    Green Xenon [Radium], Apr 23, 2008
  9. Green Xenon [Radium]

    Ken Hart Guest

    Yes. a finer grain film should be able to handle more discretely different
    loudness levels, however, the film developement will determine will the
    first and last loudness level will be. (There are films which are designed
    to render exposure as either black or white- such films, while very fine
    grained would yield little dynamic range.) To continue your analogy (which
    isn't really far off), imagine setting all the lower bits to one (or zero).
    Or imagine setting the higher bits all to zero (or one). Under developement
    or over developement could cause this. Additionally, (just to throw a
    curveball into your analogy!), the bits in the middle are not evenly spaced.
    I think that if you check out the response curve of different films, this
    may become more clear, or hopelessly muddled! Film doesn't have a straight
    line response to the amount of light hitting it. Whether that response
    matches audio's log curve, I don't know.
    Ken Hart, Apr 23, 2008

  10. It seems here that a finer grain density can handle both a louder volume
    [without clipping] and higher frequencies [without aliasing] than a
    coarser grain.

    Does an audio track with finer grain density have any disadvantage when
    compared to an audio track with coarser grain? I wouldn't think so at
    this point but I could be wrong.
    Green Xenon [Radium], Apr 29, 2008
  11. Green Xenon [Radium]

    Ken Hart Guest

    Fine grain films generally are slower speed, that is they require more light
    for exposure.

    You need to look into the response curve of the film in question. If you
    were to raise the volume at a linear rate and the exposure light increases
    at a linear rate, the film may or may not react at a linear rate. Different
    films respond differently and the manufacturer's curves will show that.
    On the other hand, human hearing response is not linear either. Just
    guessing, but I suspect a linear response is not the best bet.
    Ken Hart, Apr 29, 2008
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