35mm mono optical sound always 2 tracks ?
Thierry De Vries
I was wondering if 35mm optical sound has always been 2 tracks. I've
searched the internet and can't find any definitive answers. I'm under
the impression that (especially since Dolby Stereo, mid seventies)
that optical sound has been recorded on film with 2 tracks even if
it's mono (resulting in 2 identical tracks). Is this true ? And if so,
has it always been that way (even with the earlier formats, example
Cinemascope on http://www.widescreenmuseum.com/widescreen/wingcs5.htm)?
Thanks,
Thierry
Greg Burgmann
variable area. The variable density fell out of favour as it became noisier
than variable area as dirt accumulated on the film. (dirt on the black areas
of variable area is not read)
Later still, varaible area was recorded as 2 "track" using 1 light valve and
a beam splitter.
There are a couple of complicating issues with light valves - bias, and
valve clash
Bias is applied to close the valve ribbons as much as possible in quiet
passages (result in more black area, and less noise from dirt on the film).
But this lead to the next problem - valve clash. This occured if a loud
transient followed a long quiet passage (more than 1 second approx). In
operation, the bias will close the valve as much as possible, then the
transient will attempt to fully modulate the valve, but the clash together
(because the bias has not been removed
In later (about 1970's) sound camera manufacturers installed an extra head
before the playback head to remove the bias before loud transients.
Regards
Greg Burgmann
"Thierry De Vries" <thie...@a-sound.com> wrote in message
news:34f42cd1.02111...@posting.google.com...
Scott Dorsey
Having multiple tracks simultaneously helps null out even harmonic
distortion. Western Electric has a patent on this. I have seen tracks
with one, two, and four parallel variable area sections, all in mono.
I think Brian Coe's book on the history of movie photography might have
some discussion of this.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Peter H.
>>
Having multiple tracks simultaneously helps null out even harmonic distortion.
Western Electric has a patent on this. I have seen tracks with one, two, and
four parallel variable area sections, all in mono.
>>
Budolph's Stereo Variable-Area valve of 1938 was physically capable of
recording one, two or four discrete, time-coincident tracks.
When this valve was finally put into production in 1947, in the Western
Electric RA-1231 optical sound recorder, it was released as: 1) a
variable-density valve (by far the most popular configuration at that time),
and 2) a "dual bilateral" variable-area valve (the least popular configuration
at that time).
This valve, and its recorder, was put on the shelf shortly before 1960.
Years later, in 1976, the RA-1231 would be resurrected by Westrex/Nuoptix as
its Stereo Variable Area recorder, in a two channel discrete stereo, bilateral
variable-area configuration.
(Colortek successfully, and independently of Westrex, modified this recorder to
provide a four channel unilateral variable area configuration, but this was not
a commercial success).
One, two and five bilateral variable area tracks (and perhaps other
configurations), comprising a single mono channel have been implemented using a
galvanometer. A galvo is inherently incapable of stereo.
Beam splitters are not used to accomplish this.
Rather, the galvo's "mask" is changed to incorporate more than one track, all
of which are the same.
(The original Dolby Stereo recorders were made using two mono galvos and a VERY
complex optical system).
This optical system was a beam combiner, not a beam splitter.
Today, the most common track is Western Electric's dual bilateral stereo
variable-area track, and these recorders are still in new production by
Nuoptix.
Variable density was abandoned for two reasons: 1) the advent of stereo
variable-area meant that mono in general and mono variable density in
particular was essentially dead (although a stereo variable-area recorder is
certainly capable of making a variable area mono track), and 2) there is no
variable density sound recording stock being made.