Edge of a 35mm film print showing the soundtracks. The outermost strip (left of picture) contains the SDDS track as an image of a digital signal; the next contains the perforations used to drive the film through the projector, with the Dolby Digital track between them. SDDS stands for Sony Dynamic Digital Sound which is a cinema Sound system developed by Sony Dolby Digital is the marketing name for a series of lossy audio compression technologies developed by Dolby The two tracks of the analog soundtrack on the next strip are variable-area (RCA Photophone), where amplitude is represented as a waveform. RCA Photophone was the trade name given to one of four major competing technologies that emerged in the American film industry in the late 1920s for synchronizing electrically recorded At present, these are generally encoded using Dolby SR matrixing to simulate four tracks. The Dolby SR noise reduction format ( Spectral Recording) was developed by Dolby Laboratories and has been in common use in professional audio since 1986 Finally, to the far right, you can see the timecode used to synchronize with a DTS soundtrack CD. DTS (also known as Digital Theater Systems) owned by DTS Inc ( is a multi-channel digital Surround sound format used for both commercial/theatrical

Sound-on-film refers to a class of sound film processes where the sound accompanying picture is physically recorded onto photographic film, usually, but not always, the same strip of film carrying the picture. A sound film is a motion picture with synchronized sound, or sound technologically coupled to image as opposed to a Silent film. Sound-on-film processes can either record an analogue sound track or digital sound track, and may record the signal either optically or magnetically. An analog or analogue signal is any continuous signal for which the time varying feature (variable of the signal is a representation of some other A digital system uses discrete (discontinuous values usually but not always Symbolized Numerically (hence called "digital" to represent information for In Physics, magnetism is one of the Phenomena by which Materials exert attractive or repulsive Forces on other Materials.

Analogue sound-on-Film recording

The most prevalent modern method of recording sound on a film print is by stereo variable-area (SVA) recording, encoding a two-channel audio signal as a pair of lines running parallel with the film's direction of travel through the projector. A release print is the reel of film that is sent to a movie theater for exhibition The lines change area (grow broader or narrower) depending on the magnitude of the signal. The projector shines a light or LED, called an exciter, through a perpendicular slit onto the film. The image on the small slice of exposed track modulates the intensity of the light, which is collected by a photosensitive element, a photodiode or CCD. A photodiode is a type of Photodetector capable of converting Light into either current or Voltage, depending upon the mode of operation A charge-coupled device ( CCD) is an analog Shift register, that enables the transportation of analog signals (electric charges through successive stages (capacitors

Commonly, the audio signal recorded onto an SVA track is encoded through a phase matrix, which allowed the two-channel format to record a center and surround channel, and companding noise reduction, which allows a constant signal-to-noise ratio to be delivered over a wide dynamic range. Matrix decoder is an audio technology where a finite number of discrete audio channels (e In Telecommunication, Signal processing, and Thermodynamics, companding (occasionally called compansion) is a method of mitigating the detrimental Signal-to-noise ratio (often abbreviated SNR or S/N) is an Electrical engineering concept also used in other fields (such as scientific Measurements

Earlier processes, used on 70mm film prints and special presentations of 35mm film prints, recorded sound magnetically on ferric oxide tracks bonded to the film print, outside the sprocket holes. 70 mm film (or 65 mm film) is a wide high-resolution film gauge of superior quality to standard 35 mm motion picture film format. 35 mm film is the basic Film gauge most commonly used for both still Photography and Motion pictures, and remains relatively unchanged since its Iron(III oxide —also known as ferric oxide, Hematite, red iron oxide, synthetic maghemite, colcothar, or simply Rust —is

Sound-on-film formats

Almost all modern motion picture sound formats are sound-on-film formats, including:

Optical analog formats

• Fox/Western Electric (Westrex) Movietone, are variable-density formats of sound film. Western Electric Company (sometimes abbreviated WE and WECo) was an American Electrical engineering company the manufacturing arm The Movietone sound system is a Sound-on-film method of recording sound for motion pictures which guarantees synchronisation between the sound and the picture A sound film is a motion picture with synchronized sound, or sound technologically coupled to image as opposed to a Silent film. (No longer used, but still playable on modern projectors. )
• RCA Photophone, a variable-area format now universally used for optical analog soundtracks - since the late 1970s, usually with a Dolby encoding matrix. RCA Photophone was the trade name given to one of four major competing technologies that emerged in the American film industry in the late 1920s for synchronizing electrically recorded

Encoding matrices

• Dolby Stereo
• Dolby SR
• Ultra Stereo

Optical digital formats

• Dolby Digital
• Sony Dynamic Digital Sound

Obsolete formats

• Fantasound, where sound and picture were recorded on separate strips of film, introduced for initial release of Disney's Fantasia (1940)
• Phonofilm, patented by Lee De Forest in 1919, defunct by 1929
• Cinema Digital Sound, an optical format which was the first commercial digital sound format, used between 1990 and 1992

Further reading

• Movietone
• Sound film
• Vitaphone
• Phonofilm
• Photokinema
• sound-on-disc
• List of film formats
• Joseph Tykociński-Tykociner

See also

• Optigan