Sound-on-film

The optical sound is the oldest and still in use today sound film process are applied in the image and audio information on the same carrier. The sound of a movie is this wide on a maximum of one tenth of an inch ( ie a maximum of 2.54 mm), soundtrack strip called between frames and the sprocket holes of the film recorded photographically. A major difficulty with this method is that the sound must be sampled by the constant current film strip, while the images are conveyed gradually. Therefore, the picture and sound staggered on the carrier are stored, see time offset.

As an alternative to the optical sound Magnettonverfahren used. Opposite the Magnettonverfahren the optical sound has several advantages. Firstly, the soundtrack is also copied when making the films, so no additional steps are required. Secondly, the soundtrack is stable over time and can not be deleted accidentally. Drawback is ( as in the actual movie image as well) the susceptibility to scratches, which can lead to sound distortion.

History

The optical sound was the first method in which the sound is recorded on the same carrier medium as the file. It was first introduced to the public by Sven Berglund 1921 and demonstrated on 9 June 1922 in the United States by the Polish engineer Józef Tykociński - Tykociner. A few months later showed the German engineers Hans Vogt, Joseph Massolle and Jo Engl, their first films. The first film with integrated optical sound track, The arsonist producer Erwin Baron, was performed in Germany in 1922 in the Berlin Alhambra light games. The rights in the procedure were sold in 1928 to William Fox. The technique was not limited solely to the film. For example, the world's first speaking clock worked from 1933 also in Paris by this method, after the mechanical scanning in the experimental operation did not meet the high requirements for continuous operation. The first commercial success with the optical sound in film was the inventor Lee de Forest, who in 1960 received an honorary Oscar for it. However, it is reported that he had stolen in the early twenties his classmate Theodore Willard Case at Yale, the idea of ​​the sound film.

Since 1976, the optical sound worked with the Dolby A noise reduction system. This system improved the Lichttonqualität so significant that it was now possible, two optical tracks to accommodate the same room, on the earlier one was, and still accommodate the information for a surround channel and a center channel in these two tracks. That was the beginning of Dolby Stereo. Since 1987, the Dolby Spectral Recording Noise Reduction (Dolby SR ) was used. Accordingly, called the optical sound Dolby Stereo SR or simply Dolby SR.

Recording principle

For the production, there are two methods: The intensity method ( scion font ) and the amplitude method ( jagged script ).

Intensity method ( scion font )

The sound is recorded on the film strip in constant width, the blackening or density, however, is variable, which is caused by the amplitude depending on the varying degrees of light in film production. The period of recorded wellenfömigen density is the quotient of film speed and the audio frequency. The resulting recording on the film strip is referred to as the son of Scripture. By using two stereo sound tracks can be achieved.

One of the first inventor who devised a sound recording according to this principle, Heinrich Stefan Peschka was.

Amplitude method ( jagged script )

When amplitude method is the audio encoding, surrounded by high density, recorded jagged on the filmstrip. The amplitude determines the width variations of the spikes, the frequency of their periods. The resulting image is called jagged script. The deflection of the teeth on either side then determined one channel of stereo sound - the production of stereo two tracks are not necessarily required here. Upon deflection in two directions is called the font and double jagged script. Usually two double prongs tracks are used for analog stereo recording.

Color of the sound track

In color films, the color of the track depends on the method. While mostly a black and white soundtrack is used, set the early color film process Cinecolor a blue soundtrack. This was not ideal for playing with the usual projectors.

Digital processes

There are now digital optical sound tracks such as Dolby Stereo SR- digital, nowadays usually called simply Dolby Digital ( the most widely used digital Sound Mix ), or SDDS, a system developed by Sony.

In this method, unlike the sound is not copied analogous to the film to analog optical sound, but digital information that is collected by a photodetector and are then converted into a decoder for audio signals.

These methods allow a more dynamic, less vulnerable to damage and more channels, allowing a better spatial imaging and more creative freedom in tone. Furthermore, the soundtracks applied redundantly with Dolby Digital and SDDS, ie that even with damage to individual images, the entire sound signal can be reconstructed.

At system DTS sound is not stored on the film, but only a time signal ( timecode ), which is used to synchronize the image and stored on an external CD -ROM sound. The distribution of DTS is declining because many film distributors shy away from the increased logistical effort involved.

There are extensions of these digital systems to more channels, for example DSRDEX as an extension of DSR -D ( Dolby Digital).

THX is not a separate sound system, but a certification process for optimized sound. These are elements of the sound system, as well as the acoustics and optics checked in cinema halls and certified. However, the proclaimed by THX quality improvement is controversial among experts.

Reproduction principle

A small lamp on the soundtrack, the more depending on the amplitude and frequency of the recorded audio signal varying degrees of light to pass through ( analog sound storage ). Thus, light falls varying intensity on a photodiode (or earlier, a photocell ) which is fixed on the other side of the film. The photodiode converts the light into an AC voltage, which is amplified and then fed to the loudspeakers in the cinema. A slit aperture ensures that only a very short piece of the soundtrack is illuminated in order to reflect as well as high frequencies.

Offset between image and sound

The images come when projecting a moment to stand and be illuminated by the projector lamp. For this, a piece of film between free-swinging loops is stepped. The audio must be read by a constant current piece of film it. Therefore, image and sound track are offset to the screening copies to each other. The sound device called the capstan, which is connected to a flywheel for a peaceful path ensures uniform film.

The sound and image distance is standardized for all film formats and Sound Mix, but not always the same. This is true for both analog and digital methods alike.

Brand name

In the United States optical sound were common in the 1920s under the following brand names:

  • DeForest Phonofilm was patented in 1919 by Lee De Forest intensity method, which was after 1929 but no longer in use.
  • Movietone was one of Theodore Caste and Earl I. Sponable 1925 developed from DeForest Phonofilm method that was used in 1926 by the Fox Film Corporation.
  • RCA phono Phone was in 1925 by General Electric patented and soon taken over by RCA amplitude method, which was used by Walt Disney, RKO, Republic Pictures, Warner Bros. and 20th Century Fox.
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