|Explaining Surround Sound|
|Home Theater Feature Articles Audio Related Articles|
|Written by Jerry Del Colliano|
|Thursday, 13 December 2007|
I don’t blame you if you are confused by all of the audio/video acronyms that go along with surround sound. The moron who thought that real people would intuitively be able to figure out all the surround sound options currently on the market should be working in another field. AudioRevolution.com is going to give you the basics on the most important surround sound features for music, movies and more.
Discrete Surround Formats
Dolby Digital or AC3 – Dolby Digital is a compressed discrete surround sound format that is dominant on DVD-Video movies and is frequently found on DVD-Audio discs. Most receivers and AV Preamps are capable of decoding Dolby Digital. Dolby Digital’s main advantage is that it can fit in places where uncompressed surround sound simply wouldn’t go. One of those places is on some satellite TV broadcasts. You do need a Dolby Digital-capable DSS (digital satellite) receiver, but it is nice to get movies from the dish in surround. Music enthusiasts argue that the 12:1 compression on Dolby Digital loses a little too much audio quality as compared to other “lossy” surround sound formats like DTS.
DTS – DTS was developed for “Jurassic Park” in 1993 and is the main competitor to Dolby Digital in the AV market. DTS’ advantage over Dolby is its 3:1 compression versus 12:1. While the sound is often better, studio and record labels have to decide if they want to sacrifice supplemental material on a DVD in place of better surround sound. DTS has produced many of their own musical titles on CD, DVD and DVD-Audio that feature their surround sound format: DTS CDs can be played on any CD player with a digital output or on a DVD player. Any good receiver or AV preamp you would consider purchasing will certainly have DTS and Dolby Digital.
MLP – MLP stands for Meridian Lossless Packing. It is the “Lossless” compression scheme used on DVD-Audio to get the highest resolution surround sound and stereo music from a DVD disc. For the most part, MLP needs an analog output from a player into a preamp to supposedly guard against piracy, although digital interfaces are now appearing, especially on expensive players and receivers. Dolby Digital and DTS can flow straight out of your digital output from your player or satellite receiver and into your receiver.
DSD – Found exclusively on SACDs (Super Audio CD), Sony and Philips’ DSD format uses a different recording and compression scheme than the PCM (Pulse Code Modulation) used by DVD-Audio and all other digital media. Recording engineers argue the pros and cons of PCM vs. DSD, but in your system, both sound better than a 16-bit CD.
What do all of the numbers mean?
“5.1” – 5.1 is one of the most confusing audio terms ever invented. Some genius decided on this to describe the typical surround system, consisting of the five surround speakers (center, two fronts, two rears) used, plus a subwoofer. Because in early systems (such as Dolby), the Low Frequency Effects (LFE) channel was limited only to low frequencies, it was referred to as “.1” – who knows why. The LFE channel is often referred to as the “subwoofer” channel, but that is a big mistake. The LFE channel on a DVD does not go to the subwoofer -- it goes into your system’s bass management. Similarly, the subwoofer doesn’t just receive signals from the LFE, but instead receives all the bass from all channels that your other speakers can’t reproduce, thanks to the bass management system.
5.1 surround sound is traditionally configured with the following speakers: front left, front right, center, rear left, rear right and subwoofer. You can have 6.1, 7.1 and more but nearly all systems and practically all software are designed for 5.1 operation.
DTS ES (6.1) – DTS has a format that most frequently adds a rear center speaker to the surround sound package found on selected music and movie discs. Many receivers come equipped with DTS ES, but the software is sometimes hard to find.
THX EX (7.1) – As Nigel Tufnel from Spinal Tap would say, “But this one is one better – isn’t it?” He is probably right, and if you have the discs and a preamp that can play 7.1, you can add more speakers to your system to increase your system’s ability to resolve detailed and complex surround effects from more modern films. THX EX suffers from the same problem as DTS ES, i.e., apart from the new “Star Wars” films, people are hard-pressed to name any movies in the format. There are more, but they are not well publicized; however, many enthusiasts clients demand 6.1 and 7.1 functionality from their gear.
Quadraphonic – If you were the coolest guy on your block in the 1970s, you likely had a quadraphonic system. While quad laid an egg commercially, mainly because of the limitations of vinyl as a surround sound medium, many tasty recordings were made in quad during the 1970s. Some of these have been released on DTS CDs. Others, like Pink Floyd’s Dark Side of the Moon, are making their way to SACD or DVD-Audio. You may think quadraphonic sound went the way of the Quaalude, but it is still kicking around.
Ambisonics – Although quad was by and large a disaster, there was one system that worked quite well – and still does. This system is called Ambisonics. A team in Britain invented it at the end of the quad era in the early 1970s. The basic principle of Ambisonics is to capture or create a soundfield in the most natural and efficient way, transmit it with an efficient number of channels and replay it with a number of speakers you can reasonably place in your listening room. Ambisonic recordings, pioneered by companies like Nimbus Records, use a special microphone called a Soundfield mic, or a multitrack mixer with Ambisonic controls. Four channels are all that’s needed to transmit that information, including height (and it can use a matrix system – see below – called UHJ to make it stereo-compatible). A decoder in the receiver decodes the signal to suit your speaker layout. Nowadays, Ambisonics is fully digital, and in fact the DVD-Audio specification includes provision for carrying the signals. Ambisonic recordings can easily be decoded for 5.1 speaker systems and some manufacturers include the provision for it in their receivers and preamps. The “Trifield” three-speaker stereo technique is also derived from Ambisonics. Several DVD recordings use Ambisonic technology, but are decodes in the studio to suit 5.1 replay systems, so you may not be aware that the system is being used, apart from noticing extremely good surround localization and a more realistic surround soundstage than you generally find in current recordings.
In the days before multi-channel digital audio systems like DVD, surround (originally quad, but later other systems as well) had to be squeezed into two channels for compatibility with stereo broadcasts and albums. This was never as good as having extra “real” channels, but as few people actually had four-channel tape recorders or record players, it was the best that could be done. The process of squeezing four or more channels into two and then trying to get them back again at the receiving end is called “matrixing” and the systems that do this are called “Matrix Surround” systems. Dolby, because of their prominence in the film world, became the leader at this with Dolby Pro Logic and now Pro Logic II.
Many TV broadcasts are actually transmitted in surround using this system – look for messages at the beginning saying, “in surround where available” – and if you switch your receiver to “Pro Logic” or “Pro Logic II,” you will be able to listen in surround. The Pro Logic decoder in your receiver or preamp will also do a fair job of creating a surround effect from ordinary stereo material, although some have a special “Super Stereo” mode for this that may do a better job in some cases.
Pro Logic II is leaps and bounds ahead of the old Dolby Pro Logic. Pro Logic II can add significant information to your rear speakers, which really adds to watching satellite TV, digital cable, playing video games, watching movies from a VCR and more.
Any good receiver today has some sort of matrix surround format. Most have Dolby Pro Logic II. It is something worth testing before you make your decision. In a perfect world, everything you watched or listened to would be mixed and mastered for lossless surround. In reality, much of the best programming and content needs a little help. A good receiver or preamp can do that.
Don’t be intimidated by all of the buzz terms and code words. Understand that your AV system will perform well with all sorts of surround sound formats. Understanding the difference between uncompressed, somewhat compressed and matrix surround fields will make the job of investing in a new receiver or preamp much easier. Also, don’t be fooled by industry hype. It is cool to be an early adopter, but before you buy a product with a hot new surround format for your system, make sure the format has enough titles to warrant your decision. The good news is that even some of the more entry-level receivers are now offering software and firmware upgrades that can be downloaded from the Internet and uploaded to your components via a CD rom. Look into this capability when you are making an investment in a surround sound component. It will give your AV preamp more longevity, resulting in more value over the years for you.