Stereo was the original multi-channel cinema sound format from which all todays' home and cinema sound systems are derived.
INTRODUCTION
MONO
STEREO
QUAD
DOLBY STEREO
DOLBY SURROUND
DOLBY PRO-LOGIC
DOLBY DIGITAL
DOLBY DIGITAL-EX
DTS
DTS-ES
MPEG-II
SONY SDDS
THX
TIMELINE

Sound Formats

 

STEREO

The term 'stereo' in today's world refers to a format carrying two channels of audio information developed for playback through two speakers, one channel for each speaker. The first 'stereophonic' recordings used in the cinema actually contained three channels of audio rather than the normal two. The three channel stereo for cinema use was created by Bell Laboratories in the 1930's and, in 1941, Walt Disney Pictures released the animated classic 'Fantasia' with the first three channel stereo soundtrack. The audio information was recorded as optical tracks onto a separate 35mm film and was synchronized with the movie. The third channel created effects from surround speakers placed at the sides and the back of the theater (see Dolby Stereo and Dolby Surround below). In the 1950's a fourth audio channel was added to carry dialogue for a speaker placed behind and in the centre of the theater screen. The idea behind the centre speaker was to lock the attention of everyone in the theater to the screen. With two speakers, people seated at the sides of the theater would commonly hear the closest speaker at a louder volume which destroyed the stereo soundstage. The centre speaker, in addition to providing dialogue to the screen, filled the gap between the two front speakers and created a soundfield at the front of the theater that was much more realistic than in a system with two front speakers. The two channel stereo we enjoy today in television and hi-fi systems originated in 1958 when vinyl LP's began to carry stereo. The third and fourth surround channels were abandoned for this format because LP's could only hold two channels of information. Therefore, two speakers were used and the hi-fi we know today was born. FM radio began to use two channel stereo in 1961, followed by the compact cassette in 1970 which employed Dolby B noise reduction.