Film - A Practical Guide to Video and Audio Compression - page 59

When working with 16mm film, the audio bandwidth will be higher. The audio
bandwidth of 35mm film should go well beyond the audible range of a human ear,
depending on whether it uses a magnetic stripe or an optical track on the edge of the film.

4.10 Magnetic Stripe for Sound Recording

There is certain to be some interesting archival material in people's attics, and during the
1960s a small UK-based company called SuperSound developed a method of adding a
stripe of magnetic tape down the sprocketed edge of the film so that a sound track could
be added. Figure 4-14 shows where the stripe was placed.
Wider-gauge film required a balancing stripe so that the film could be spooled
evenly. Adding the stripe reduced the amount of film that could be carried on the spools
because it was thicker and couldn't therefore wind as tightly. Note also that the stripe is
on the emulsion side. Be aware of this when scanning because it offsets the emulsion away
from the focal plane of the scanner, and this might slightly blur the scanned image.
The development of this striping technology spawned a successful business that
either added the stripe to customers' films or sold them the equipment and materials to
do it themselves. Figure 4-15 shows a photograph of the striper unit that you could buy
and use at home. These were marketed all over the world during the 1960s, which means
there may be significant quantities of archival 8mm material out there that also has an
interesting sound track.
Film stock was available in monochrome and color and was based on a 16mm stock
that was turned over after the first pass through the camera. The film was then slit down
the middle during processing and spliced together before sending back to the photogra-
pher. Typical film roll sizes were 25, 50, 100, and 200 feet long. A roll of 16mm stock
was supplied on 25-foot spools and played for about 4 minutes when slit and returned
from processing as a 50-foot reel. The exact time depended on the shooting frame rate,
which could be between 18 and 24 fps. This short duration somewhat limited the creative
possibilities, although some enthusiasts edited together programs of several hours at
what must have been an extraordinarily high cost.

Stripe

Optional balancing stripe

Emulsion

Substrate

Figure 4-14 Placement of the magnetic sound stripe on the film.