Comments on the history of attaching sound to film

Pictures with sound are just taken for granted and have been for over sixty years, except for the amateur, who had to be content with silent film until the advent of Super 8mm cameras with a magnetic stripe. But we now are all so familiar with sound that, if it was silent the first thought would be, “There’s something wrong with this!” And that’s going way back long before the arrival of Video Cameras.

Sound recording was being gradually developed from before the turn of the Century, but they couldn’t get it onto film. So, by the time that silent films became well established with many famous stars, especially in America, it was all in fact, exaggerated miming and movement was the novelty! For a long time, hand-cranked cameras were used and the cameraman had to operate with a handle cranked at two turns per .second. So there was an inevitable variation in speed! The films, when shown, were accompanied by a pianist to help set the mood.

When, in 1927, a ‘Talkie’ arrived, there was so much excitement with people queuing to see The Jazz Singer, a feature film, that it made Al Jolson a famous star overnight. ‘Talkies’ had arrived, but it was really the same old method of recording on a gramophone record that was a much larger disc, and it had to be synchronised with the picture. Not very satisfactory, for if the film was broken and a few frames were lost, it was immediately out of sync.
 

Shortly after this, research into sound on film was speeded up and the ‘Vitaphone’ was superseded by ‘Movietone.’ This allowed perfect synchronisation of the picture and sound, ‘The Soun4 Track!’ Two kinds of track were invented, though the principle of replay was exactly the same: ‘Variable Area’ and Variable Density.

With variable area, the film passes over a narrow slot, with a lamp behind and thin blades on either side of the slot (or a blade on one side). The sound modulates the voltage, which lengthens and shortens the slot. The resulting, image is transferred photographically onto the film and can be seen as a black line with modulating width on the sound track.

With variable density, the slot remains constant at the width of the track, but the light modulates according to a voltage proportional to the sound received. This is seen as lighter and darker areas on the sound track.

So with both methods, a photographic image is created. When the film is running through the projector the film goes through the intermittent gate, then the movement is smoothed on the sound drum and the photographic sound track passes over a slot which modulates the light from an exciter lamp before it falls on a photo-electric cell. This method gives high quality sound and is still in use today, though mostly superseded now by multiple magnetic sound tracks.              John Woolmer