How to add sound to amateur films (1954)

playback in step with the picture. Corrections'are made on the tape as necessary and the sound is transferred to film only when pronounced satisfactory. Synchronisation of the sound negative and picture can be checked quite readily by spooling them together on a common reel and lacing both films through the same projector. The sound negative is clear over the picture area and so will not interfere with projection. You should avoid lacing the picture film round the sound head, however, as it will interfere with the sound reproduction of the sound negative. Synchronisation Marks When you thread two films through the projector in this way, you must see that the picture and sound are correctly synchronised. The sound must reach the sound head when the corresponding picture is in the gate. The sound head is 26 frames below the picture gate and consequently the sound track must be set 26 frames in advance of the picture. If you examine a sound film closely, you can often identify particular parts of the sound track. You will then find that the recording of an impact is not printed opposite the picture of the impact. Instead, it is opposite the frame projected just over one second earlier. You can easily adjust the synchronisation of picture and sound so long as they go through your projector as two separate films. So although the synchronisation must be correct to within two frames or better you can readily achieve this by trial and error. However, when the married print is made from your two negatives, the laboratory people will not want to determine the correct synchronisation in this way. You want a married print with the correct 26-frame advance of the sound: the laboratory needs a quick way of seeing you get it. This is why you must put synchronisation or sync, marks on the leaders of the sound and picture negatives. You make a sync, mark by scratching two lines diagonally 59