DVD Sound

DVD Player Primer | DVD audio | What is Surround Sound | DVD Intro | DVD FAQ

DVD is a Digital Video Disc, but the audio considerations are important enough to warrant their own consideration. In fact audio considerations are often as numerous - and possibly more confusing - than video ones.

DVD Audio formats:

DVD - Dolby : DTS

DTS or Dolby Digital

When you look at DVD audio specs, you are likely to encounter two types :

• DTS (Digital Theater Sound)
  
• Dolby Digital (this might also be called AC-3, but it is the same as Dolby Digital).

What is the difference between Dolby Digital and DTS? DTS is newer and is capable of producing slightly better (the difference in audio quality might be undetectable audibly by humans) sound, but both DTS and Dolby Digital are 5.1 channel systems. What does that mean? It means the sound is processed into 6 separate paths.

The 5 channels are center, front right, rear right, front left, rear left, and the .1 stands for the subwoofer (really low bass). This allows you to have a theater-like surround sound with the center channel mimicking the dialog and the other channels giving the sound from everywhere else.

Decoders and compatibility

Look to see if your DVD player is "compatible" or has "decoders." Some models are just "compatible" with these sound systems and better ones will have what are called "decoders" built right in. Decoders actually separate the sound into those discreet 5.1 channels and send them to the appropriate places. And those places are 6 separate output jacks on the back of the DVD player. So, if you want the benefit of those separate channels, your Audio/Video receiver must be equipped to handle them with 6 separate inputs. In other words, they need to match.

That's important because it means that if your DVD player is part of your home entertainment center, then the sound will only be as good as what your receiver is capable of. There is no reason to plop down $1000 on a DVD player with onboard DTS decoders if your receiver only has stereo left and right inputs.

Other feature considerations

DVD players can also play music CDs. Some DVD players will also handle DVD Audio. These are essentially CDs made on DVD discs to take advantage of DVD's higher sampling rate (a "higher sampling rate" is capable of superior sound). 

DVD player setup for surround sound

Stereo

Stereo sound first came to the home in the early 1960s and revolutionized home audio  entertainment. Compared to mono, two channel stereo sound was seen as a tremendous improvement, and stayed that way until Dolby Surround came to  the video market.

Dolby Surround

Dolby  Surround first debuted in theaters in 1979 and was available in the home by 1982. These original home theater Dolby Surround decoders could only decode the  left, right and surround channels. It wasn't until the early '90s that Dolby  Pro Logic decoders appeared that could decode the center channel as well.  Dolby Pro Logic surround is an analog (not digital) format, with the rear surround channels in mono only.

Dolby Digital 5.1

Dolby Digital (originally known as AC-3)  was first heard in theaters in 1992. The Dolby Digital specification for surround  sound consists of five separate audio channels and a bass channel. Unlike Dolby Pro Logic, whose rear channels are mono and do not have the full  dynamic range as the front set, Dolby Digital provides up to five discrete audio  channels, all with full dynamic range. This means that with a 5.1 system you can hear the film as the director intended, with sounds all around you and thumping  bass.

Digital Theater Systems

DTS is also a digital 5.1 surround system, but the  audio is far less compressed than Dolby Digital. DTS is therefore the choice of  audio purists, although in a normal home theater set-up the difference may be difficult to detect. But as DTS is less compressed, few DTS DVDs have extras or  foreign audio tracks.

What Do I Need For Dolby Digital 5.1?

Your route into Dolby Digital will depend largely on whether you already have any home theater components, and how much money you have to spend. These factors will determine which of the two routes below are best for you.

Internal Dolby Digital Decoding On A DVD Player
If you already have an older home theater amplifier that doesn't have a Dolby Digital  decoder, then your best bet will be to buy a player with its own decoder. With this set-up, the decoded audio is sent out of the back of the DVD player via the phono outputs into the six inputs of your amplifier.

External Dolby Digital Decoding Using An Amplifier
The other option is to invest in an  amplifier which has its own built-in Dolby Digital decoder. This option will suit people who don't have a decoder in their DVD player, or people who want to use the highest quality components in their system. This option handles the  decoding by lifting the Dolby Digital track off the DVD and sending it out to the amplifier for decoding via either a digital coaxial or optical audio cable.

For Internal Decoding

For External Decoding

DVD Player >>

Must have an onboard Dolby Digital  decoder.

Can be equipped with or without an internal decoder.

Amplifier >>

Must be able to accept 5.1 external inputs (6 cables).

Must have an onboard Dolby Digital  decoder.

Connection >>

RCA phono cable.

Digital Coaxial or Optical cable.

A 5.1 soundtrack will contain six distinct channels of audio for the positions of left, center, right, left surround, right surround and the Low Frequency Effects (LFE, bass or ".1") channel. Unlike the analog Dolby Surround and Pro Logic formats, Dolby Digital has two independent surround channels. This means that a 5.1 system will give a far greater sense of depth and localization than a Pro Logic system. The LFE channel is a separate channel that allows the inclusion of low frequency bass sounds that are felt more than heard in the theater. The LFE channel can be routed to either a separate subwoofer or to all five speakers individually. If even Dolby Digital isn't good enough for you, consider a DTS compatible sound system.

Also available, but much rarer, are DVDs with 5.0 Dolby Digital soundtracks. These discs offer the same 5 channel surround sound as 5.1 discs, but don't carry an LFE channel to provide the low frequency bass.

DTS, full name Digital Theater Systems, made its debut in theaters in 1993 with Steven Speilberg's Jurassic Park. Like Dolby Digital, DTS is an audio codec (meaning to code/decode) that can allow anywhere between one channel (mono) and six channels (5.1 surround) of digital sound. However, DTS uses less than one quarter the compression of Dolby Digital, meaning a DTS soundtrack is much closer in quality to the studio master. DTS audio offers more subtle nuances, giving individual sounds superb clarity; better dynamic range, meaning the loudest bangs have more depth and the quiet passages are free of noise; and finally, improved channel separation across the 5.1 spectrum, for greater localization of sound around the room. But because it's less compressed, the DTS soundtrack takes up more space on the DVD, meaning DTS discs often come with fewer extras or foreign language tracks.

Most DVD players available today will be able to handle DTS, either by using DTS Digital Out to pass the bitstream to an external amplifier for decoding, or by using its own internal DTS decoder. If you are interested in purchasing a player with DTS, or want to check whether your current player supports it, look for the DTS logo, such as the two below, on the player or refer to the player's instruction manual.

Identifying Dolby Digital soundtracks on DVD

English: 5.1
Spanish: Dolby Surround
German: stereo

Dolby Laboratories has developed icons which can also be used. to distinguish formats. For example:


English (5.1)
Spanish (Dolby Surround)
German (stereo)

Audio Connections for DVD soundtracks

Audio connections can be either analog or digital. Analog connections will typically be in the form of stereo (right and left) RCA connectors, whereas digital connections will either use a single RCA coaxial connection, or a single optical (toslink) connection. Different sources will have different connection options, and some equipment does not give you the choice of an analog or digital connection. If you are unsure which connection options you have, please refer to your owner's manual or the audio connectors on the back of you equipment.

If you have the choice between an analog or digital connection (for this to be true, the source will always have to be digital), it is important to focus on the fundamental processing differences between analog and digital connections. The fundamental difference has to do with where the digital to analog conversion takes place, using a Digital Audio Converter or DAC.

All digital sources must be converted to analog in order to be produced as sound. Making a digital connection transfers the digital signal from the source to another piece of processing equipment (such as a receiver, a pre/pro amp, or an outboard DAC) to be converted to an analog signal. Making an analog connection uses the DAC's on the source component for the digital to analog conversion, which will transfer the signal as analog from the source. The main purpose of making a digital connection is to take advantage of higher-quality DAC's in another piece of equipment. Another motivation for making all digital connections whenever possible, is to use the same Digital Audio Converters for all the digital sources, thus creating some congruency in how the digital sources are translated to analog. For example, by using the same DAC for both CD audio and DVD audio, the audio from your CD player will sound virtually the same as the audio from your DVD player.

Analog Audio Interconnect: Transfers a stereo (right and left) audio signal by using a two-channel cable. If the original source is digital, then the signal must be converted to analog on the source piece of equipment in order to utilize the analog audio connection. However, this stereo signal may be converted to some type of matrixed surround format, such as Dolby Pro Logic, via the processing equipment (receiver, pre/pro amp, etc.) that the signal is sent to.

Coaxial (Coax) Digital Audio Cable: Transfers a digital audio signal, via electricity traveling down a copper wire, over a shielded 75 Ohm coaxial cable. 75 Ohm RCA connectors are used on both ends. The jack for this connection looks like this:







Optical (Toslink) Digital Audio Cable: Transfers a digital audio signal, via a red light beam, over a fiber-optic cable. A fiber optic cable is comprised of many small strands of polished plastic specifically designed to transfer light. The jack for this connection looks like this:






The performance difference between Coax and Toslink connections is negligible. That is not to say that each connection cannot sound different, though. Any audible difference between the two connections stems from differences in the quality of the electronics, NOT the type of connection. For example, if a CD player uses superior quality components for its Coax digital audio connection and inferior components for its Toslink connection, then it is reasonable to assume that the Coax could have superior sound quality. The bottom line is, neither type of connection is inferior to the other for digital audio connections. Both connections are equally suited for multi-channel digital audio.

If you ever have to choose between these two types of connections, performance will basically be a moot point. So, how do you choose? Well, lets look at the physical characteristics of each cable/connection.

A Coaxial cable is more sturdy and durable than a digital optical (Toslink) cable. However, due to the metal shielding and conductor, a Coax cable may transfer grounding problems from one component to another if they already exist. Basically, if there are ground loop problems stemming from electrical abnormalities in the electronics, the cable may carry ground or "hum" noise from one component to the other. However, these problems are fairly rare, and the Coax cable will ONLY exhibit the problems if they already exist. It will NOT create any new ones.

An optical (Toslink) cable, on the other hand, is more fragile than a coaxial cable. If stepped on, a Toslink cable can be crushed and possibly destroyed. However, an optical connection is immune to possible ground or "hum" problems because it does not contain any metal.

There are also usability differences between the two cables. A Coax cable uses a standard male RCA plug, which is very easy to plug-in. On the other hand, a Toslink cable uses a quasi-pentagonal connector, which must be aligned properly to be inserted. It will only go in one way, which makes it a lot harder to work with. With most equipment racks requiring us to become a contortionist with near-perfect night-vision to make any sort of connection, the ease of use of the familiar RCA is a good thing!

Summary: With everything else being equal, a Coax digital audio connection would be your first choice simply because a Coax digital audio cable is more durable, easier to use, and less expensive (in most cases) than a similar quality Toslink cable.

Columbia ISA Audio Video
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