Sound follower

On the set, a clapperboard is used to mark the spot where the sound and picture will later be aligned in editing.

[5] Typical sound followers lock to the power line using a sync motor and toothed timing belts, or by using 240 Hz bi-phase interlocking pulse signals to sync sound to film.

[8] In telecine use, the 24 frames per second is slowed to 23.976 frames/s to lock to SDTV and some HDTV standards, thus the digital bi-phase pulse is 239.76 Hz.

So, a two-hour movie with previews uses 11,250 feet or 2.13 miles (3.43 km) of film.

[11] The Sepmag would follow a projector or a telecine or a hand-cranked or motorized film viewer on a workbench.

The tracks are very large and the magnetic film moving at the normal speed of 24 frames per second, gave very good sound reproduction.

35 mm mag films may not be fully coated, but "striped" to permit editing marks to show through both sides.

It is generally accepted that Everest Records subsidiary of the Belock Instrument Corporation based in College Point New York pioneered the use of three channel 35 mm magnetic film from around 1959.

Improvements in standard tape technology and the high cost of the 35 mm process led to its discontinuance.

[citation needed] Sound followers are not used for most new film productions (the major exception being IMAX).