Surround Sound Systems - Dolby Digital, DTS, THX & HD Surround

What Is Surround Sound?

Surround sound refers to the use of multiple audio tracks to envelop the movie watching or music listening audience, making them feel like they're in the middle of the action or concert.  The surround sound movie soundtrack allows the audience to hear sounds coming from all around them, and plays a large part in realizing what movie makers call "suspended disbelief".  "Suspended disbelief" is when the audience is completely captivated by the movie experience and is no longer aware of their real-world surroundings.

True surround sound formats rely on dedicated speakers that literally and physically surround the audience.  There is one center speaker which carries most of the dialog (since the actors usually speak while making their on-screen appearance), and part of the soundtrack.  There are left and right front speakers that carry most of the soundtrack (music and sound effects), and may carry parts of the dialog (when the director wants to intentionally off-set the source of the dialog to either side, from its default dead-center screen location).  There is a pair of surround sound speakers that is placed to the side (and slightly above) of the audience to provide the surround sound and ambient effects.  Finally, a subwoofer can be used to reproduce the low and very low frequency effects (LFE) that come with certain movies

The main  true surround sound formats are :

Dolby Digital (AC-3)

Dolby Digital is a 5.1-channel surround sound format, and is the standard for DVD-Video.  Dolby Digital features up to five discrete (independent) channels (front center, front left, front right, surround left, surround right; giving it the "5" designation) of full frequency sound (with respect to the range of human hearing, which ideally ranges from 20 Hz to 20,000 Hz), plus a sixth channel for low frequency effects (LFE).  The LFE signal is usually reserved for the subwoofer speaker(s), or those speakers capable of reproducing low frequency ranges. The low frequency effects channel gives Dolby Digital the ".1" designation. The ".1" signifies that the sixth channel is not full frequency, as it contains only deep bass frequencies (3 Hz to 120 Hz).

Dolby Digital is a lossy audio encoding scheme that supports up to 5.1 channels of discrete audio.  In actuality, a Dolby Digital soundtrack may be composed of less than 5.1 channels.  For example, Dolby Digital 1.0 is mono audio (single track of audio information), while Dolby Digital 2.0 is stereo (in which Dolby Surround or Dolby Surround Pro-Logic can be encoded).  Dolby Digital 4.0 have discrete audio signals for the center, left, and right channels, plus a mono audio signal that is common for the surround channels.  Dolby Digital 5.0 is like Dolby Digital 5.1, but lacks a discrete audio signal for the low frequency  effects channel.

For DVD-Video, Dolby Digital encodes these multi-channel soundtracks at either the 448 kbit/sec or 384 kbit/sec data rates.

For Blu-ray Disc, Dolby Digital encodes these multi-channel soundtracks at 640 kbit/sec.

Keep in mind that "Dolby Digital" does not necessarily equate to "Dolby Digital 5.1".  

"Dolby Digital" generically refers to the encoding scheme as discussed in the paragraph above.  Only when it says "Dolby Digital 5.1" explicitly can you be sure that the soundtrack consists of 5.1 discrete channels.

To take advantage of Dolby Digital surround sound, you must have either:
(1) Dolby Digital decoder in the DVD player and a "Dolby Digital ready" AV receiver or pre-amplifier, or
(2) Dolby Digital AV receiver or pre-amplifier and use the DVD player's digital audio output.
      (This option is generally better since it allows the DVD player to pass the raw digital audio signal to the receiver or pre-amplifier, which theoretically is less subject to interference and degradation.) 

DTS Digital Surround :

DTS Digital Surround is a 5.1-channel surround sound format, similar to Dolby Digital. As such it is a competing format to Dolby Digital.

DTS (Digital Theater System) features up to five discrete (independent) channels (front center, front left, front right, surround left, surround right; giving it the "5" designation) of full frequency sound (with respect to the range of human hearing, which ideally ranges from 20 Hz to 20,000 Hz), plus a sixth channel for low frequency effects (LFE).

The LFE signal is usually reserved for the subwoofer speaker(s), or those speakers capable of reproducing low frequency ranges.

The low frequency effects channel gives DTS the ".1" designation. The ".1" signifies that the sixth channel is not full frequency, as it contains only deep bass frequencies (3 Hz to 120 Hz).

DTS is a lossy audio encoding scheme that supports up to 5.1 channels of discrete audio.  Though the vast majority of DTS digital surround soundtracks consist of 5.1 channels, the fact is that it can be composed of less than 5.1 discrete channels.

For example,

DTS 4.0 have discrete audio signals for the center, left, and right channels, plus a mono audio signal that is common for the surround channels.

DTS 4.1 is like DTS 4.0, but adds the ".1" low frequency  effects channel.

DTS 5.0 is like DTS 5.1, but lacks a discrete audio signal for the low frequency  effects channel.

Keep in mind that "DTS" does not always equate to "DTS 5.1".

"DTS" generically refers to the encoding scheme as discussed above.

Only when it says "DTS 5.1" explicitly can you be sure that the soundtrack consists of 5.1 discrete channels.

Fortunately, the vast majority of DTS encoded DVDs are in fact DTS 5.1.

DTS uses higher data rates (1.5 Mbit/sec or 754 kbit/sec, which are almost twice to four times higher) to encode the 5.1 channels of surround sound information than Dolby Digital (448 kbit/sec or 384 kbit/sec), prompting many home theater enthusiasts and industry experts to claim that it is superior to Dolby Digital.

DTS surround sound encoded DVD-Video titles are far fewer in number than their Dolby Digital counterparts, and until recently were released months after their Dolby Digital counterparts.

Thanks to the new lower DTS data rate (i.e., the 754 kbit/sec data rate), some studios (e.g., Buena Vista, DreamWorks, Fox, New Line and to a lesser extent Columbia TriStar and Artisan) have begun to release DVD titles that feature both Dolby Digital 5.1 and DTS 5.1.  Prior to the advent of the lower DTS data rate, DTS DVD titles featured the full DTS data rate (i.e., the 1.5 Mbit/sec data rate) soundtrack, a Dolby Surround 2.0 soundtrack (for backwards compatibility with non-DTS equipment), and few (if any) bonus material since capacity of the DVD was limited due to the "data hogging" full-rate DTS soundtrack.

To take advantage of DTS digital surround, you must have either configuration (A) or (B):

Configuration (A): DTS decoding in the receiver or preamplifier (this is the preferred configuration)
   (1) a receiver or pre-amplifier with built-in DTS decoding (look for the "DTS" logo on the faceplate), and
   (2) a DVD player with DTS digital output (look for the "DTS" or "DTS digital out" logo on the faceplate).  Alternatively you can use a DVD player with DTS decoding built-in with its digital output (in which case you're not really using the decoder in the DVD player), and
   (3) use an optical or coaxial digital audio interconnect to connect the DVD player to the receiver or preamplifier

Configuration (B): DTS decoding in the DVD player
   (1) a "5.1-channel ready" receiver or preamplifier (with no DTS decoding) that has a set of 5.1-channel analog inputs, and
   (2) a DVD player with built-in DTS decoding (look for the "DTS digital surround" logo on the faceplate and a set of 5.1-channel analog outputs on the back panel), and
   (3) use six analog audio interconnects (i.e., three stereo RCA pairs) between the DVD player and the receiver or preamplifier

Dolby Surround Pro-Logic :

Dolby Surround Pro-Logic emerged in home theater systems in the early 1990's.  It became the surround sound standard for Hi-Fi VHS, and is still the standard for today's analog TV broadcasts, since the Dolby Surround Pro-Logic signal can be encoded in a stereo analog signal.  If you have an "older" Dolby Surround Pro-Logic receiver, you can still enjoy movies from DVD-Video, since all DVD-Video players down-mixes the Dolby Digital information to the Dolby Surround Pro-Logic format, and outputs the signal as a stereo audio pair. 

Extended Surround formats: 

THX Surround EX (Dolby Digital EX)

THX Surround EX, also known as Dolby Digital EX, refers to the Dolby Digital version of the new "6.1"-channel surround sound format that extends the 5.1-channel surround sound format with one (or two) additional speaker(s) located in the back of the audience (i.e., back surround channel).  THX Surround EX is actually a 5.1-channel format with the back surround audio channel matrixed into those of the right and left surround.  The back surround channel is matrixed in similar fashion as the front center channel is matrixed into the front right and left channels in the Dolby Surround Pro-Logic format.  As such, the back surround channel is not discrete and therefore THX Surround EX is not a true "6.1" format.

To take advantage of THX Surround EX, you must have both: 
1.) a DVD player and use one of the digital audio outputs (e.g., "Toslink" optical or coaxial).
2.) a THX Surround EX decoder, usually a function of the receiver or pre-amplifier.  Look for the  "THX  Surround EX" words or logo on the faceplate.  Receivers featuring THX Surround EX decoding are still relatively expensive, particularly those that comes with six or seven channels of amplification for the full frequency channels.

DTS Extended Surround (Matrix or Discrete 6.1)

DTS Extended Surround refers to the Digital Theater Sound's version of the new "6.1"-channel surround sound format that extends the 5.1-channel surround sound format with one (or two) additional speaker(s) located in the back of the audience (i.e., back surround channel).

DTS Extended Surround (or DTS-ES for short) comes in two flavors: (1) DTS Extended Surround Matrix, or (2) DTS Extended Surround Discrete 6.1.

DTS-ES Matrix is actually a 5.1-channel format with the back surround audio channel matrixed into those of the right and left surround.

The back surround channel is matrixed in similar fashion as the front center channel is matrixed into the front right and left channels in the Dolby Surround Pro-Logic format.

As such, the back surround channel is not discrete and therefore is not a true "6.1" format.  DTS-ES Matrix is compatible with THX Surround EX equipment.

DTS-ES Matrix is completely backwards compatible with DTS 5.1 equipment.

DTS-ES Discrete 6.1 is a true 6.1-channel format, as the back surround audio channel is discretely encoded into the DTS bit stream.

This format offers better spatialization over the surround channels for complete 360-degree sound localization and surround pans (i.e., movement of sound in the surround channels from one side to another).

A data flag signals the decoder (usually part of the receiver or pre-amplifier) that the bitstream contains an extra discrete back surround channel.

For backwards compatibility, DTS-ES Discrete 6.1 back surround channel is ignored by DTS 5.1 equipment.

To take advantage of DTS Extended Surround digital surround, you must have both: 

(1) DTS-capable DVD player, either with DTS digital output or a DTS built-in decoder.  Look for the "DTS" or "DTS digital out" logos on the faceplate of the DVD player.
(2) DTS Extended Surround decoder, usually part of a DTS-ES capable receiver or DTS-ES capable pre-amplifier

Look for the "DTS Extended Surround" logo on the faceplate.  THX Surround EX equipment can decode DTS-ES Matrix, but not DTS-ES Discrete 6.1.  DTS-ES Discrete 6.1 requires a true DTS-ES decoder.
Equipment featuring a true DTS-ES decoder is still few in number and are expensive.  A few models that are currently available include the Denon AVR-5800 receiver (approximately $3,800).

: High Definition Surround Sound :

 Dolby Laboratories and DTS, Inc. have offered their own solutions, known as Dolby TrueHD and DTS-HD Master Audio respectively.  Both of these new surround sound formats offer:

• 100% lossless encoding that matches the original high quality studio master bit-for-bit for an unmatched surround sound experience.
• Up to 7.1 channels of surround sound, with two additional back channels placed directly behind the audience for a thoroughly immersive surround sound experience.
• Complete artistic control over the down-mixing of multi-channel surround sound, enabling the movie director or soundtrack mixer to specify how a 7.1-channel surround sound mix is down-mixed to 5.1-channel or even 2-channel home theater configuration.  So no matter your loudspeaker configuration, you always get the mix that the creative team intended.
  
  
  
  
  

The end result is that either of these two surround sound formats can offer an acoustic experience that matches the jaw-dropping visual experience of high definition TV.  We will talk about Dolby TrueHD and DTS-HD Master Audio in turn, then discuss how you can enjoy these new high definition surround sound formats in the new Blu-ray Disc optical media format and the audio/video equipment that you would need.

Dolby TrueHD :

Dolby TrueHD is Dolby Laboratory's state-of-the-art version of high definition surround sound that supersedes the Dolby Digital 5.1-channel and Dolby Digital Plus 7.1-channel surround sound formats.  Dolby Digital is the most popular surround sound format, prevalent on DVDs, HDTV over-the-air broadcasts, broadcast satellite, and of course cable network digital channel offerings.  While Dolby Digital is good, Dolby TrueHD is leaps and bounds better in every way imaginable, as summarized in the table that follows.

                                             Key parameters of Dolby Digital vs. Dolby TrueHD

Lossy / Lossless: Dolby Digital uses a lossy compression algorithm to encode and pack the audio information into a DVD audio track or a broadcast bitstream.

Lossy means that mathematically, the playback does not replicate bit-for-bit (the 1's and 0's of digital data) the original bitstream that was encoded.Through the science of psychoacoustics and noise shaping, Dolby Digital encodes the essence of the surround sound information.Because of the data limitations, some audio fidelity is lost with lossy encoding.  In contrast, Dolby TrueHD uses a lossless encoding algorithm based on MLP Lossless technology, used in the DVD-Audio format for multi-channel music.Lossless means that mathematically, the playback is able to re-create the original digital studio master recording bit-for-bit.

That means the audio information is pristine.  In playback, we get everything that the audio engineer produced, literally down to the last digital bit.  And that is as good as it gets!

Number of channels & typical channel configuration: Dolby Digital can support up to 6 channels in a 5.1-channel configuration.That is "5" full-frequency channels and one low frequency effects ".1" channel.Dolby TrueHD expands this to a maximum of 8 channels, adding two additional full-frequency channels for a total of "7" + ".1" low frequency effects.  Of course, the Dolby TrueHD decoding process can down mix the 7.1-channel soundtrack to playback for 5.1-channel home theater setup.

Maximum data rates: Because the Blu-ray Disc format affords greater data capacity, Dolby TrueHD soundtrack can use a data rate of up to 18 Mbps for just the surround sound information.That is about 40 times the data rate for Dolby Digital on DVD.  As you can see, that is a phenomenal leap in the amount of information that can be captured using Dolby TrueHD.

What does this do for us?  Higher data rates mean higher frequency sampling ratesand longer sampling word lengths, as described below.

Frequency sampling rate: A higher frequency sampling rate means that the sound in all frequency ranges will be encoded with more accuracy.

In everyday terms, the playback soundfield  will be more realistic and natural.  In particular high-pitched sounds within the audible spectrum with improve in tonal accuracy.

Sampling word length: Going from 16-bit word length to a longer 24-bit word length means that more dynamic range can be recorded.

Dynamic range refers the variations of loudness (without changing the playback volume) that spans from the loudest crescendos of music and an action movie explosions to the softness of a subtle nuance emanating from a supporting musical instrument and the whispers in a romantic movie.

While Dolby TrueHD is an optional surround sound format on the Blu-ray Disc format, it is very popular and is offered on many Blu-ray Disc titles.

DTS-HD Master Audio 

DTS-HD Master Audio is a high definition surround sound format alternative to Dolby TrueHD.  It is DTS Inc.'s version of Dolby Laboratory's Dolby TrueHD.  Surely, there are technical differences, but from an everyday consumer standpoint, they are more alike than different.  DTS-HD Master Audio is state-of-the-art, offering 7.1-channel surround sound that is bit-for-bit identical to the original digital studio master recording.It is available on select Blu-ray Disc titles.

                                               Key parameters DTS Surround Sound vs. DTS-HD Master Audio

Which is Better: Dolby TrueHD or DTS-HD Master Audio?

To the consumer, it no longer matters as it once did when the DVD-Video format was first introduced and the surround sound format "war" was between Dolby Digital and DTS Surround Sound.  Because both Dolby TrueHD and DTS-HD Master Audio are lossless formats that replicate the original studio master bit-for-bit and offer up to 7.1 channels of surround sound, both formats offer unprecedented, jaw dropping surround sound experiences.

What Equipment Do I Need to Enjoy These New High Definition Surround Sound Formats?

Blu-ray Disc player and an AV receiver both with Dolby TrueHD and DTS-HD Master Audio decoding built-in:

If your equipment is new, you only need to hook them up with an HDMI v1.2 cable (HDMI v1.3 recommended, minimum):
(a) a Blu-ray Disc player that decodes Dolby TrueHD and DTS-HD Master Audio;
(b) a 7.1-channel AV receiver with Dolby TrueHD and DTS-HD Master Audiodecoding; 
(c) a single HDMI v1.2 cable (HDMI v1.3 recommended, minimum) to hook up the Blu-ray Disc player to the AV receiver to pass both the video and multi-channel audio information;
(d) a second HDMI v1.2 cable (HDMI v1.3 recommended, minimum) to hook up your AV receiver to your HDTV to pass the video signal.
(e) seven full frequency loudspeakers (or five for 5.1-channel configuration) and an optional subwoofer for the "0.1" LFE channel

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