GreenXenon wrote:
On May 13, 8:43 am, Peter wrote:
On May 12, 10:42 pm, GreenXenon wrote:



On May 12, 1:23 pm, Neil Midkiff wrote:
GreenXenon wrote:
GreenXenon wrote:
I'm thinking of a theoretical device using analog audio recording on
VD optical tracks containing the oldest film chemical composition.
Blue takes up less space than green [for the same amount of data], so
I'm guessing blue would make more efficient use of the film's length.
This is because blue light is of shorter wavelength than green light.
Per area, blue can represent more info than green.
What is the best wavelength of blue to use?
You're confusing two different sorts of recording here. It's true that
in digital recording to optical discs the shorter wavelength of blue
light is an advantage (as in Blu-Ray vs. standard DVD), because that
style of recording looks at the presence or absence of individual "pits"
representing binary data, and blue light can be focused more tightly
onto smaller pits on the disc.
This has almost nothing to do with variable-density audio recording on
film, in which analog audio signals are photographed as varying gray
tones on the track.
Black-and-white film is inherently grainy; the various levels of gray in
a VD track are made up of varying densities of exposed-and-developed
grains -- starting out as crystals of a silver halide, then developed to
bits of metallic silver in the emulsion. On a microscopic scale, b/w
film is just that: opaque silver bits in a clear emulsion. It only
looks gray on a broader view, just as a halftoned newspaper photograph
made up of dots of black ink on paper simulates grayscales at ordinary
reading distance.
So it's necessary for the soundtrack to be wide enough (usually at least
a couple of millimeters) that the reading process "looks at" a broad
enough area to average out the film grain. If you used a laser spot
pickup similar to the one in a DVD player to read a VD film soundtrack,
the output would be full of random noise as the individual grains passed
by the reader.
And of course, to expose this wide a track, the sound recorder must
project the flickering light through a slit that's as wide as the track.
In other words, the area you're looking at is so much larger than the
wavelength of light that the color of the light for recording or
playback doesn't matter.
-Neil Midkiff
What determines the highest-frequency sound that can be recorded onto
a VD optical track?


The speed at which the film moves, the bandwidth of the transducer and
the intensity of the illumination, are important factors. Near the
limit of these factors, the performance of the film might be a factor.

You say intensity of illumination. Does that mean that a more intense
light can allow for a higher-frequency than a less intense light?

By transducer, I assume your talking about the photoelectric cells
that convert the optical signal playback from the film into an
electric signal to be amplified and sent to a loudspeaker. Am I on the
right track?

As for the tape speed, does the nyquist theorem apply? If so, what is
the minimum tape speed required to record a sound of 1 Hz? IOW, how
high of a frequency is allowed per speed? In devices where sampling-
rates are used, the sample-rate must be at least 2x that maximum
frequency of the input signal.

Sorry, my branch of the free university has closed down for the month.

A simple "Thank you" now and then might go a long way towards paying
your tuition for the next round of courses.

Until then, you might try actually reading a book at the public library.

-Neil Midkiff