|An Instant Introduction to 5.1 Audio|
|Home Theater Feature Articles Audio Related Articles|
|Written by Richard Elen|
|Thursday, 13 December 2007|
An Instant Introduction to 5.1 Audio
In the beginning, there was mono, which has but one channel. And mono begat stereo, which hath two channels. And stereo begat a whole set of monsters, of which 5.1 is the result.
The term "5.1" refers to the number of channels in the most common of today’s surround-sound configurations. The "5" refers to the five main channels – left front, center front, right front, left surround and right surround – while the ".1" refers to the low frequency effects channel, also known as LFE. Ideally, a 5.1 signal is provided by the source material, such as a DVD-Video disc with a 5.1-channel Dolby AC-3 soundtrack, a DTS-encoded DVD or compact disc, or, increasingly, a satellite TV channel. In many cases, the source is a matrixed surround source, often a two-channel signal containing embedded surround information such as Dolby Stereo. A signal like this is decoded into 5.1 by a special decoder (a Dolby Pro Logic decoder in the case of Dolby Stereo). The results can be impressive. However, a "discrete" source like a DVD, in which the channels are isolated in production to play as separate yet concerted tracks within your home theater system, sounds far superior.
What kind of set-up do you need for a good surround listening experience? Start with your DVD player. It should be capable of outputting high-definition digital signals, not just common "CD-quality" digital audio but, if possible, the latest, nearly master tape-quality, 24-bit, 96 kHz signals, either via coaxial digital cable or "TOSLink" optical cable. It should be able to play not only Dolby Surround and DTS-encoded DVD discs, but also stereo and DTS-encoded compact discs.
5.1 music discs (CDs, DVD-Video and DVD-Audio) offer an impressive surround music experience, which is distinctly different from that of watching a movie with surround sound. Some of these surround CDs are transfers of classic "quad" recordings from the past, while others are brand-new mixes created especially for the medium. In either case, you’ll enjoy the extra dimension that surround adds to your music listening.
Likewise, your receiver or preamp should be equipped with both Dolby Digital and DTS decoders to decode the vast majority of surround sources available today, from HDTV and satellite movie channels, surround CDs and DVDs, to the latest DVD-Audio discs. The amplifier will have separate outputs for the three front speakers (left, center and right), the two surrounds (left and right) and a subwoofer for very low frequencies (the "point-one").
It’s a great idea, if you can afford it (and if you have somewhere to put them) to have full-range speakers for front and rear. If you can’t stretch that far yet, at least get full-range speakers for front left and right, and get a center speaker and surrounds that sounds good with them – perhaps from the same manufacturer. In my own system, for example, I have JBL speakers all round, but the front units are full-range, while the surrounds and the center front are smaller. Yet they sound enough alike that the big front speakers plus my powered subwoofer provide depth and punch for the whole system. The smaller rear speakers give a good surround effect, while the center front speaker is great for dialogue in a movie.
Even if you have full-range speakers all round, you’ll find that a sub-woofer is a worthwhile investment. Movies in particular often have very powerful effects and the subwoofer really adds a physical element to the experience. Generally, your amplifier will have a preamp output to drive a self-powered subwoofer. This is because the sub takes a lot of power and needs an amp of its own, often built into the actual subwoofer speaker cabinet.
There are film industry standards that suggest where to locate the speakers in a 5.1 system for a movie theater, and if you were going to do nothing but watch movies with surround sound at home, they would work fine. However, the speaker positions in a movie house don’t correspond very well with the need you may well have for your home theater system to replay stereo effectively, with the front speakers at 60 degrees (which is probably where your front speakers are).
Luckily, modern home theater systems take this into account, and often include sophisticated set-up features – see your receiver or AV preamp's manual for details. These allow you to tell the system, for example, how far away the speakers are, whether they are large or small, and whether or not you have a center-front speaker and/or a subwoofer. You can often also tell the system whether the surrounds are behind you or on either side of you when you’re seated in the listening position, and adjust the levels of the individual speakers for the best surround sound effect.
It’s worth spending some time setting up and fine- tuning your system. The effect is greatly improved if you follow the instructions, make sure that your speakers are in the right places and adjust the balance between the channels. Your receiver or preamp will probably have a test signal you can use to get the relative levels right. Don’t worry if you find yourself tweaking the levels over the course of a few days. It is perfectly normal. I even adjusts the sub level of my receiver for different types of source material to suit my taste in each specific listening experience.
Although 5.1 was originally designed for movie theaters, and the surround channels – and the LFE – were intended originally for effects purposes, 5.1 is now being used very successfully for music. Modern music surround is extremely impressive, with a growing number of music DVDs and surround-encoded CDs available, while DVD-Audio and Super Audio CDs are just around the corner.
Not only is 5.1 surround sound the perfect companion for home movie viewing and high-definition television (HDTV), but it is also the ideal listening environment for a new, more powerful, more enveloping audio experience. Whether you’re watching a movie or listening to your favorite band or orchestra, 5.1 surround hits the spot with the sound of tomorrow. 5.1 succeeds where stereo fails by giving artists, producers and music engineers the discreet and highly resolute tools needed to create a dramatically better and more emotionally involving musical experience. Pick up a bunch of recorded albums and listen to them: the effect can be stunning.