Dolby this and DTS that....format names can be confusing. There are a profusion of surround sound names. While Dolby formats are the most popular, DTS comes a close second. It would make good sense to have a little understanding of what the format names mean. This article explains them.
Stereo sound, the original 2 channel stereo, added a spatial dimension to sound reproduction. What that really meant was that, the listener was able to spatially identify the location of the instrument or the vocal playing as if he was facing the stage performance. As applied to the movies, it meant that we were able to identify the location of the speaker, on the screen rather than getting a jumble of sounds from the general area of the screen.
Ever since, sound reproduction improvements have tried to achieve this realism. A second effort has been to add the immersive dimension. If the stereo, in general, helped a listener resolve sound sources in the horizontal scale, there remained the gap in front of the listener to be covered. The surround channels that reproduce sound from the back helped add that dimension in front and from behind the listener. If the sounds you are hearing in front are supposed to reverberate from the hills at your back, the reproduced sound can recreate that feeling. Here is a set of articles on the surround sound audio formats in depth.
Original 2 channel stereo had a right and a left speaker. Quite often that left a “hole in the wall effect” or lack of detail in the middle. So, as a first improvement a central speaker was added. That also helped add details on the screen which were typically between the two main speakers. Two rear speakers or the surround speakers added the audio that was supposed to come from the back. That added up to the use of 5 speakers. Then a sub-woofer (aka Low frequency effects or LFE) was added to the front array that reproduced really low frequency sounds. Thus was born the 5.1 speaker system.
You also get 6.1 and 7.1 speaker arrangements. In the 6.1 arrangement you add a central speaker at the back too. In the 7.1 arrangement there are two speakers left back and right back beside the two surround speakers. In some sound formats two of the surround speakers may be driven by the same audio channel as in matrix arrangement. Discrete sound systems drive each speaker with a unique audio channel. As we get into home theaters with large screens you need to graduate to a home theater arrangement of at least 6.1 or better still 7.1. Do remember that each of these channels carry sounds that are slightly delayed from each other and reach our ears at different times. This is what simulates the delays related to sound generated at different spots on screen and sound from the back. Equipped with that knowledge, let’s look at the surround sound recording formats now.