Going from Dolby Surround to 5.1 audio
Dolby Pro Logic, the dark ages
The advent of 5.1 audio allowed for a more viable and pleasing home theater movie watching experience over the older Dolby Surround sound tracks that relied on 2 channels of audio, decoded by a process known as Dolby Pro-Logic to create 4 channels of audio: Front-Left, Front Center, Front-Right, Mono-Rear-channel (usually split into 2 channels, but possessing the same audio information in each). Receivers and processors with Dolby Pro-Logic decoding would do all the work.
Dolby Pro-Logic would basically take the 2 channels (the left and right channels usually from a source like a VCR or LaserDisc player) and create the 4 channels in this manner: The Front-Center channel was produced by taking the signal common to both the left and the right channels and steering them into the Front-Center channel. The new Front-Left was the left channel information that wasn't common to the right channel, the new Front-Right was the right channel information that wasn't the common to the left channel, and the rear channel as created from out of phase audio from the combined left and right channel.
Sounds convoluted, right? It also SOUNDED convoluted when it was played back as well.
Dolby Surround was an audio presentation that was problematic in the bleed through from either of the 2 channels into the 4 channels. Most of the time, the center channel seem to get all of the audio information, leaving the front-left and front-right channels with little to do. It did not create a realistic enough surround sound environment for home theater enthusiasts like you!
Then DVDs were invented. Yay!
5.1 Channel Audio, the modern era
To achieve the surround sound environment of a movie theater, a majority of DVDs today come with audio that allows a receiver/processor that is capable of decoding a single digital audio track (usually encoded as Dolby Digital 5.1, sometimes dts 5.1) that comes from the DVD player, into 5 discrete channels of full range audio, and a .1 discrete channel that is limited to bass frequencies and is known as the Low Frequency Effects (LFE) channel.
So, now you will see this number "5.1" everywhere you look around here. It means an audio format that has 5 main speakers (regular left and right like a normal stereo system- and added to that a center speaker to go between the left & right speakers. And then you have two surround speakers that go behind you for surround effects)-- and you have the .1 speaker which is the special channel for just bass.
The receiver or processor handles it all
Receivers can be thought of as the control center of your home theater. It contains amplifiers to power your speakers, it allows you to switch from source to source for audio and often video, it allows you to adjust many HT setup parameters, and it processes digital audio tracks and splits them into discrete channels of audio for the speakers.
Processors do the processing of the digital audio tracks. Processors can be either standalone, or built into a Pre-amp. If they feed a pre-amp, the discrete channels of audio are connected from the processor to the pre-amp in the form of cables with male RCA jacks on each end. These cables are referred as "InterConnects", and to get good performance, choose a shielded cable rated at 75 ohms, these are the same type of cables that will be referred to as Digital Coax cables later in this article.
As long as you select the right input on the receiver/processor so that it knows which input to process, you're almost home free in getting 5.1 audio.
Most pre-amps with built-in processors are referred to as Pre-Pros because they do everything a receiver does with the exception of supplying the power for the speakers (you'd use separate amps to power the speakers).
Receivers will take in the digital audio input from the DVD player, and process it, and direct the 5.1 discrete channels of audio to the proper amplifier channels, which will power the proper speakers. The 5 main channels feed the following placed speakers: Front-Left, Front-Center, Front-Right, Rear-Left, and Rear-Right. The .1 channel is fed into a subwoofer, and requires amplification from the subwoofer to play the signal back properly (some Powered Subwoofers are powered by a self-contained amplifier onboard, other Passive subwoofers require a separate amplifier to power it).
Along those same lines, a processor will take in the input signal, process it, and produce 5 discrete channels of full range audio, plus the .1 LFE channel. Sending the 5.1 discrete audio channels to a Pre-amp (via InterConnects) will allow you to adjust the levels of each channel in case you need to lower or boost a channel to provide a more cohesive sound environment (this can usually be done with a receiver as well). Then the "corrected" audio channels are sent to amplifiers which are connected to the properly placed speakers.
Hooking up the DVD player for digital sound
That about covers the Receiver/Processor side. Let's turn our attention back towards the start of all this mess, the DVD player:
So, you have 2 types of connections from the DVD player:
1. A cable that has RCA jacks on each end (refered as a Digital Coax cable, which sounds fancy, but the main ingredients are that each end is terminated with RCA male connectors, and the cable itself needs to be a shielded 75 ohm rated cable to ensure proper operation/connection/impedance matching between the DVD player and the receiver or processor).
2. A cable with a small square-ish plug on each end, and the cable itself is made of a fiber-optic material. Sometimes this is known as a TOSLink cable.
The majority of the digital output from a DVD player will be the TOSLink variety. But there will always be some players that have the digital Coax RCA output as well. They offer the same functionality.
It is essential to get into the DVD player's setup settings and select what digital output stream you want your player's digital audio output to output. Consult your player's manual for the proper setting (usually it is called the Digital bitstream, rather than PCM, which is for CD playback for the most part).
When the receiver/processor processes the digitial audio signal and produces 5 full range channels and the LFE channel, the channels are mixed by the makers of the DVD's audio tracks so that when played through properly positioned speakers in a HT setup, the 5.1 channels of audio will produce a surround sound environment that envelops the viewer/listener all around them, and creates a more believable setting for the contents of the DVD, whether it be a film, a music concert, and documentary, etc.
So what the heck is 6.1?
As you check out your options for obtaining 5.1 audio in your home, you'll come across 6.1 audio, and the simple fact of the matter is that there are a few DVDs that include digital audio tracks that will allow the receivers/processors that can handle the 6.1 digital audio tracks and produce not only the usual 5.1 discrete channels of audio, but also the Rear-Center audio channel for a more complete 360 degree enveloping surround sound setup in your home. To get 6.1 capability, it'll mean looking for a new receiver/processor that can handle those DVDs encoded with 6.1 audio.
The 3 main flavors of 6.1 audio are:
Dolby Digital EX Surround
dts ES Surround
dts ES discrete surround
The first two types use a matrixing system to "encode" a 3rd rear channel inside the audio for the regular two. On these tracks there are really still only 2 real "discrete" encoded tracks-- but they are created in such a way to make a 3rd (the rear center) able to be extracted using signal processing. Like the center and surround in pro logic (which are extracted from processing a simple stereo file)- a processor is able to take the audio signal and extract a rear center channel from an compatible signal.
For the DVDs with a DD EX compatible 6.1 track, there's USUALLY a flag set in the bitstream which will tell the 6.1 decoder to activate and extract the extra rear matrixed center channel from the 2 rear channel information (however- this decoder feature can also be activated manually).
In addition to these matrixed systems- DTS offers a "discrete" 6.1 channel configuration that is (happily) backwards compatible with current 5.1 DTS decoders. Again- in this case, a flag is present to tell a compatible 6.1 DTS system to play back the audio track in 6.1.
In addition to this formats- There are receivers/processor that do faux multichannel processing which uses DSP to extract even more extra channels from a surround track. There are even forms of EX processing that are different from the Dolby or DTS EX processing, which use similar DSPs to extract a rear center channel from a 5.1 signal (see the OUTLAW 1050 receiver for an example of this).
Unless you have to have the latest and greatest in surround sound formats, it's not paramount in choosing receivers/processors that include 6.1 processing, and 5.1 audio is good enough for most HT enthusiasts. But, sometimes: the more, the merrier!
The following is an up-to-date
DD-EX & DTS-ES encoded movies listing