"GreenXenon" wrote in message
...
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?- Hide quoted text -

- Show quoted text -



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.

Since analogue recording does not involve sampling the
Nyquist criteria as applied to sampling systems does not
directly apply. However, there is a similar limitation based
on the slit length (length, width and height are releated to
film movement, slit length here means its dimention in the
direction of film motion). When the slit length is equal to
a half wavelength there is cancellation of the output. So,
just as in analogue magnetic recording there can be a series
of peaks and dips in output as the frequency is increased
(sinX/X function). The recorder can do something similar but
the effective slit length is dependant on the type of
recorder. For moving mirror recorders as used by RCA the
slit is constant for both variable width and variable
density records. For records made by ribbon light valves as
used by Western Electric/Westrex the slit length varies with
the sound intensity so that these are known as variable
exposure time recorders where the moving mirror type has
constant exposure time. Thus the effect of film reciprocity
failure is different for the two systems.

I don't understand what the previous poster was getting at
by stating that the intensity of light affected maximum
frequency, perhaps he will elucidate.


--
Richard Knoppow
Los Angeles
WB6KBL