8mm Forum: Still Learning "Optical Sound" why is it better?

This is topic Still Learning "Optical Sound" why is it better? in forum 16mm Forum at 8mm Forum.

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Posted by Pablo Alvarez Roth (Member # 655) on April 02, 2007, 11:48 PM:

I was wondering,

Amazed about the optical sound system, I looked though the internet learning how the pincipal of optical sound works.

I understood that it works basically by converting the intensity of the light by fotoreceptive cells into electrical pulses that translate it into sound "basically".

But there is some things I still don´t understand and I am very curious:

1) I understand that some 16mm films are Dual Variable Area Soundtrack and these are "MONURAL or MONO sound tracks" and not stereo, but why were these dual lines better that just 1 line (tecnically speaking)

2) Do most 16mm projectors read these 2 optical lines like my eiki SL-0?

curious Pablo!

Posted by John Whittle (Member # 22) on April 03, 2007, 03:50 PM:

There are many variations of optical sound tracks from unilateral (single edge) to bilateral to dual bilateral and Maurer even made one with six modulated lines. The more modulated lines, the less the chance of distoration due to mis guiding the film in the reader of the projector (so peaks won't be cut off).

The other sound system was variable density which was made by the telephone company (Western Electric and projectors were made by a division called ERPI [Electrical Research Products, Inc.]. In that system light is modulated by ribbons which are moved by electrical impluses which the ribbons are clamped in a strong magnet.

The area tracks originally were made by a glavo moving a mirror that moved the light against a mask in the shape of a v or w for bilaterial or dual bilateral tracks.

Warner Bros used a shuttered bilateral track (you'll see it on all the 16mm prints of cartoons that are original warners prints) where you think it's dual bilateral from the two lines but only the inside is modulated as the shutter moves out. This was done for better noise reduction (in their opinion).

Obviously a unilateral track can be quite noisy since half the film is always clear and any dirt or digs will pop and hiss in the sound, hence the efforts for ground noise reduction (the term for making the track dark where there was no sound).

John

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