Combined Prints : Magnetic or Optical

To make a magnetically striped print you must first ask a laboratory to prepare a mute print on single perforated stock. You can then arrange for a coating of ferrous oxide to be applied to the edge of the film opposite the sprocket holes. The master magnetic final mix, recorded in the dubbing theatre, can then be replayed on one machine and simultaneously re-recorded on the magnetically striped print. Care must be taken to record the track with the correct sound advance as we shall see in a moment. This laborious process has to be carried out for every single print. Combined optical sound copies are easily produced in bulk. They are also considerably cheaper.

Magnetic stripe and optical sound compared

To make optical sound combined prints, the master magnetic final mix must first be re-recorded as a photographic optical sound negative. The negative, when processed, can be synchronised and printed with the editied camera original on positive stock. Optical soundtracks/are visible. You can see fluctuations on the edge of the film. A recording on a magnetic stripe is invisible. You can see the stripe but you can not see the sound modulations. The sound can only be heard by replaying it via a magnetic soundhead.

Sound advance

We will begin by considering the term “sound advance”. If you look at any 16mm film projector you will notice that the sound head and picture gate are separate. The film runs from a feed reel through the picture gate and on round a sound drum out to the take-up reel. Sound and picture are thus separated. This is because movement through the picture gate is intermittent. The picture is advanced frame by frame by a claw. Movement round a sound drum however, must be smooth at a constant speed if the quality of the sound is to be acceptable. The distance between the picture gate and the sound head is known as the sound advance. For 16mm optical sound combined prints the sound must be advanced 26 frames. For 16mm magnetically striped prints, the sound must be advanced 28 frames.

Combined optical sound copies, are known as “comopt” copies, and magnetically striped copies as “commag”. When picture and sound are on separate pieces of film the terms “sepmag” or “double headed”, are generally used.

COMBINED PRINTS: SOUND ADVANCE

Sound and picture separation
Projector picture gates and soundheads are separated by a set number of frames. The number is internationally standard, so films made in different countries are interchangeable. On a 16mm combined magnetic sound film (A) the sound is advanced by 28 frames. On 16mm combined optical prints (B) the sound is 26 frames advanced. Movement through a picture gate is intermittent. Movement round a soundhead must be smooth. The sound advance ensures that sound and picture can both be satisfactorily reproduced.