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Variable Density

From Chace Audio

Variable Density, or V/D, refers to a type of mono optical soundtrack that resembles a bar code located between the picture frame and sprocket holes on the film. V/D tracks vary in shades of clear, gray, and black, and these shades are directly related to print density – hence the term variable density. Light shining through the variations of clear, gray, and black on the film can be played back as sound. On a V/D print, the lighter portions represent loud sounds and the darker portions are quiet. V/D frequency response is the same as that of Variable Area (V/A) soundtracks (approximately 31hz to 12.5kHz).

V/D recording began at the turn of the century and by the mid 1950s it was mostly phased out with the introduction of V/A tracks. After a brief transitional period, V/D tracks were completely discontinued. V/D tracks employed Academy pre-emphasis for noise reduction. A soundtrack from this era would have been played through a horn speaker located behind the picture screen. Because the screen physically obstructed high frequency sound waves, pre-emphasis was used to increase the level of high frequencies in the soundtrack so more high end would reach the audience.

The V/D soundtrack is visible on the left hand side in this film clip of President Calvin Coolidge.

This cartoon from the early sound era describes a method of recording a variable density track. Yes, the professor IS talking to a rolled up film clip.

The barcode-like image at the left hand side of this print is the variable density track.

vdprint.jpg