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 Monophonic system - The simplest of sound systems is monophonic called mono in short. In the older times at the invention of audio systems only one channel was recorded and tapes or even the tape heads used to be in mono or single channel. A single full range speaker used to be used for the same and today it is non existent for hifi but with the exception in the case of telephones or mono speakers in the TV and old radios. The overall effect lacks the sense of dimension. Some of the mono systems are now antique pieces..!
 Stereophony (stereo) - Human hearing is with two ears and hence the stereo was made the standard for hifi audio listening with two audio channels. It is now the accepted standard even for FM transmission and receivers do have mono playback of stereo. To get the stereo separation, speaker placements have to be with enough separation. Ideally 5-6 fts. This gives realism by introducing the width of sound.
Surround sound - Stereo gives the width of the sound. But what we actually hear in a concert hall also has reflection of sound from the walls which is the true picture of live listening. To create more realism or sort of depth to the sound, though it is an illusion, a 3rd channel was introduced which could be a delay or echo as in real life. This was termed as surround and is achieved in principle by a delay/combination of left and right etc. adding a rear center or a front center in mono format.
Quadraphonic(quad) - This originally produced 4 channels out of the stereo by processing the left and right and synthesizing sound for the extra two channels. 4 speakers in 4 corners of the room was the luxuary in quad. They had a L+R in pair added to give the surround sound as in a live concert hall where lot of mixing of sound would be happening from the echo and reflections from the walls. This was more of an effort to create the theatre realism in the olden days by phase modulation and delay. The amplifiers and speakers did the job. Then there was also the true quad systems with 4 separate channels where the recording was also in 4 channels. Now they are nearly extinct. |
