Thursday, June 11, 2015


It was the summer of ’69. We’re not talking about the Bryan Adams song here; we’re actually referring to first time surround sound became available in the home. At the time, it was called Quadraphonic sound, and it first came to home audio buffs by way of reel-to-reel tape. Unfortunately, quadraphonic sound was very short-lived. The technology, which provided discrete sound from four speakers placed in each corner of a room, was confusing — no thanks to electronics companies battling over formats (sound familiar?) –and it ultimately failed in the consumer market.
The idea that one could immerse themselves in a three-dimensional sphere of audio bliss was not to be given up on, however. In 1982 Dolby Laboratories introduced Dolby Surround, a technology that piggy-backed a surround sound signal onto a stereo source through a process called matrix encoding. Not long after, Dolby brought us Pro-Logic surround and has since done its part to advance the state of surround sound in the home to the point where as many as eleven speakers can be used to put listeners right smack in the middle of the action, be it a concert or a battle in deep space.
Unfortunately, surround sound, for many, remains a confusing technology. Though most understand the concept of using multiple speakers for theater-like sound, many don’t understand the difference between all the different formats. There’s 5.1, 6.1, 7.1, 9.2, Pro-Logic IIx, Pro Logic IIz, Dolby DSX and more. It’s a lot to wrap your head around.
With this guide to surround-sound formats, we hope to provide a little clarity as to what separates these different surround-sound versions.


For the purposes of this discussion, “matrix” has nothing to do with the popular film series featuring Keanu Reeves and Lawrence Fishburn (aside, perhaps, from the fact that the movies still make for a pretty effective surround sound demo). In this case, matrix refers to the encoding of separate sound signals within a stereo source. This approach was the basis for early surround-sound formats like Dolby Surround and Dolby Pro Logic, motivated in part by the fact that there wasn’t enough space for discrete information on early audio-video media, such as the VHS tape.

The Speakers

Surround sound, at its most basic, involves a set of stereo front speakers (left and right) and a set of surround speakers, which are usually placed just to the side and just behind a central listening position. The next step up involves the addition of a center channel: a speaker placed between the front left and right speakers and primarily responsible for reproducing dialogue in movies. Thus, we have five speakers involved. We’ll be adding more speakers later (lots more, actually) but for now we can use this basic five-speaker arrangement as a springboard for getting into all the different surround formats.

Pro Logic

Using the matrix process, Dolby’s Pro Logic surround encodes separate signals within the main left and right channels. Dolby was able to allow home audio devices to decode two extra channels of sound from media like VHS tapes, which fed the center channel and surround speakers with audio. Because of the limited space on VHS tapes, matrixed surround signals came with some limitations. The surround channels in basic Pro Logic were not in stereo and had a limited bandwidth. That means that each speaker played the same thing and the sound didn’t involve much bass or treble information.

Dolby Digital 5.1 / AC-3: The benchmark

Remember Laser Discs? Though the medium was first invented in 1978, it wasn’t until 1983 when Pioneer Electronics bought majority interest in the technology that it enjoyed any kind success in North America. One of the advantages of the Laser Disc (LD) is that it provided a lot more storage space than VHS tape. Dolby took advantage of this fact and created AC-3, now known better as Dolby Digital. This format improved on Pro-Logic in that it allowed for stereo surround speakers that could provide higher bandwidth sound. It also facilitated the addition of a low-frequency effects channel, adding the “.1” in 5.1, which is handled by a subwoofer. All of the information in Dolby Digital 5.1 is discrete –no matrixing necessary. With the release of Clear and Present Danger on LD, the first Dolby Digital surround sound began to hit home theaters. Even when DVDs came out in 1997, Dolby Digital was the default surround format. To this day, Dolby Digital 5.1 is considered by many to be the surround sound standard, and is included on most Blu-ray discs.