8mm Forum: Why Variable Area prevailed over Variable Density?

This is topic Why Variable Area prevailed over Variable Density? in forum General Yak at 8mm Forum.

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Posted by Raleigh M. Christopher (Member # 5209) on June 19, 2016, 08:47 PM:

Anyone have a clue as to why variable area prevailed over variable density when it came to optical analog soundtracks?

[ June 20, 2016, 10:42 AM: Message edited by: Raleigh M. Christopher ]

Posted by Kenneth Horan (Member # 3) on June 19, 2016, 09:56 PM:

Variable area is easier to process and print, especially on Eastman color stock. Variable density was more common in the black and white and dye-transfer Technicolor era because the soundtracks were silver.

Posted by Allan Broadfield (Member # 2298) on June 20, 2016, 04:10 AM:

As an ex lab technician, we found that an advantage of variable area was that it tended to be more tolerant of over or under exposed tracks, which was helpfull when getting acceptable results when printing dupes from varying quality archive material. Variable density would be quite garbled if print density was heavy.
One advantage, however of variabĺe density tracks was that it was more tolerant of missaligned projector sound heads, as the sound modulations covered the whole width of the track area.

Posted by Steve Klare (Member # 12) on June 20, 2016, 09:23 AM:

I wonder how they recorded master optical tracks in the first place.

To do it at film speed, you'd need some variable light source that could operate fast enough to follow the speed of the signal. An incandescent bulb would be way too slow unless you slowed the recording speed down to a crawl, but then you'd have trouble preventing overexposure.

These days, LEDs are more than fast enough, but there were optical tracks back into the 1920s and 30s. and we've had LEDs since maybe the late 1960s.

-and even that would only record variable density, not variable area.

Posted by Raleigh M. Christopher (Member # 5209) on June 20, 2016, 12:45 PM:

Found this thread over on the large gauge exhibition forum;

Variable Density vs. Variable Area

Posted by Brian Fretwell (Member # 4302) on June 20, 2016, 05:53 PM:

I thought variable area tracks were recorded using a mirror galvanometer and variable density using another method. Looking it up I find that the other method was called a light valve and both could produce both sorts of track, the light vale by changing its angle to the film. I haven't bee able to find a picture of a Light Valve but think it must be something like the thermionic valves (or tubes in the USA) that were used as level meters in some reel to reel tape recorders. IE the higher the level the more of the phosphor lit up.

Posted by Kenneth Horan (Member # 3) on June 20, 2016, 06:29 PM:

The light valve, invented in 1923 by Edward C. Wente, is a mechanical shutter using very thin wire ribbons to modulate the light to expose the soundtrack. It was used by Western Electric to produce the variable density record. Before that, an AEO light which was easily modulated by electrical signals, was used to record a variable density record. This AEO light system, called Movietone, was invented by Theodore Case and Earl Sponable. It was used by Fox Film and Universal from 1928 'til 1929 (Universal) and 1931 (Fox). Universal made the very first all talking sound-on-film feature, "Melody of Love" (1928) using this Movietone system. Fox used it for music and effects on "Sunrise" (1927). Since even slight errors in printer light settings and sensitometry and densitometry control will affect the quality of a variable density track, variable area became the standard.

Posted by Lindsay Morris (Member # 3812) on June 20, 2016, 06:32 PM:

One of the biggest drivers to switch to variable area was that it was much easier to produce a Stereo track with VA methods than using VD methods.

Variable Density though had a big advantage in that any scratching of the sound track area had less of an impact than similar scratches on a Variable Area track.

Another plus was that Variable Density tracks were great to help operators finely tune the sound optics purely by eye...no meters and other bits & pieces just a bit of white card & careful adjusting did a brilliant job.

Posted by Steve Klare (Member # 12) on June 20, 2016, 06:58 PM:

quote:
The light valve, invented in 1923 by Edward C. Wente, is a mechanical shutter using very thin wire ribbons to modulate the light to expose the soundtrack.

That's cool! We don't really think in terms of mechanical solutions to these kinds of problems these days.

-but where there's a will, there's a way!

Posted by Andrew Woodcock (Member # 3260) on June 20, 2016, 07:05 PM:

Indeed!

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