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

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
tracks.

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.


Regards,

Radium

 

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
sentence!

 

<complete snip>
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Group: sci.optics
My optical tape records audio optically on a tape using variable-density
....
8:54pm by Green Xenon [Radium]
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In variable-density optical track, what determines the frequency ...    
Group: rec.audio.tech
Green Xenon [Radium] rec audio tech Hi: In magnetic
....
Apr 18 by Green Xenon [Radium]
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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]
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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
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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
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Anyone sell string samples that sound this good?      
Group: rec.audio.pro
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
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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
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Different Formats for Different Countries -- Variable Density ...    
Group: rec.photo.film+labs
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      
Group: rec.arts.movies.tech
Variable density needs a very good gray scale, hence a linear transfer
....
May 11 2003 by Radium
----------

 

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?

 

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 wrote:

What is the finest grain that can be achieved?

 

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.

 

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.

 

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.

 

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.

 

snip

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.