Chapter 21 - Audio 3D

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In sound engineering, it is common practice and in fact advisable, to decentralize the sound sources on the stereophonic sound field, so that the individual sounds may stand out more. By acting on the panoramic controls [Panpot ] , on the frequencies, on delays and other factors such as reverb time, we can virtually place the sound source wherever we want. Say for example we wanted a sound to appear to be coming from far away, what we would do is appropriately lower the high frequencies (seeing that by their very nature they are more easily attenuated than low frequencies as distance is increased) and increase reverb (to give the impression that the sound has travelled a great deal before it reaches the listener). All this can be done with stereo systems, which as we know, entail the use of two separate channels: left and right. In the music world this is still the method that is used, and for the moment there are no foreseeable big changes on the horizon. However, in the audio-video field things are a little different in that there are additional factors to be considered, which is why as time has progressed sound diffusion systems have become more and more elaborate. Naturally the most innovative ideas have come from cinema because at first only this context could afford such highly elaborate and expensive equipment. Only recently have lowering prices allowed the public to purchase surround systems specifically made for home-use called home theatre systems.

The following is a table which summarizes the most important steps in technological innovation brought to the cinematographic audio field:

Table 21.1. Evolution of sound diffusion systems in cinema 

Mid 1800s The first techniques are developed; first attempts at tapping into the brain's faculty of linking as one stream different images projected in sequence and at high-speed.
End of 1800s Thomas Edison presents the Kinetophone. The images are fixed to a flexible film and sound is sent out on a separate media support system which is not in synchrony with the images.
1902Leon Gaumont presents a projector system connected with two phonographs. The experiment fails due to synchronization problems.
1907 The 35 mm format begins to be used.
1917 The Technicolor industry begins its first experiments with colour.
1902-1920 Attempts continue to be made in trying to get sound in synchrony with video. At that time the technology was still not sophisticated enough to achieve any substantial results.
1930 The first experiments in multichannel sound reproduction take place at the Bell Labs.
1941 First public projection of the film Fantasia using a 3-channel audio system (Left - Center - Right).
1950 Films are now projected with stereo sound (4 or more channels).
1952 Cinerama System: audio is recorded onto a magnetic tape attached to the film. It consists of 6 channels: 5 round the front and 1 on the back.
1972 First videotapes.
1976 Dolby stereo 35 mm. Audio is recorded onto two optical tracks on the film.
1976 Dolby Labs' MP Stereo system is used for the music soundtrack of the film Star Wars.
1978Dolby Stereo 70 mm.
1982Dolby Surround (3 channels, L-C-R)
1986Stereo TV (2 channels)
1987 Dolby SR (4 audio optical tracks with Dolby SR) - Dolby Pro Logic Surround (4 channels).
1991 Dolby Stereo Digital SR 5.1 (5 channels + 1 with Dolby SR).
1992 Dolby Surround Digital 5.1 (5 channels +1).

Among the countless surround systems that have been created, one deserves particular attention, namely the system created specifically for the film Fantasia by Disney engineers together with Bell Laboratories and developed in the early 1940s. For the first time ever, a system comprising 3 to 8 independent loudspeakers was used for reproducing sound in a film. Clearly at the time cinemas weren't equipped with such advanced technology, and therefore each time the engineers had to set up an audio system called Fantasound in the hall where the film was to be projected. A staff of technicians would take care of mixing the sounds live every time a projection took place, automation being totally absent at the time. They did exactly what modern-day Service engineers do at concerts.


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