.: Discreet Surround Sound Formats
Dolby
Digital
 Dolby
Digital or AC3 – Dolby Digital is Dolby's third generation audio coding
algorithm and is counted as the format of choice for most form of home entertainment
programming namely commericial DVDs, HDTV broadcasts and is being used for
digital cable and satellite transmissions for channels like HBO, Showtime
etc.
The
format accommodates left front, center front, right front, left surround,
and right surround channels, plus a separate low frequency effects (LFE) channel
that is fed to your system's subwoofer. Add that up and you get the 5 main
channels plus the ".1" LFE channel. This LFE (Low Frequency Effects)
channel handles the lowest bass in recorded digital audio from 80 Hz down.
The
encoder of Dolby Digital is been designed to exploit the selective frequency
sensitivity of the human ear and masking so as to allow audio programming
at lower data rates with a minimum of perceived degration of sound quality.
Use
is made of perceptual encoding where the system dynamically determines the
number of bits of data to be alloted to a given channel of audio information
based on judgements of its importance to the sound perceived by the listener.
The algorithm divides the audio spectrum of each channel into narrow frequency
bands of different sizes optimized with respect to the frequency selectivity
of human hearing.
- Sounds
which are below the audibility threshold for the human ear should not waste
bits which could be devoted to a higher fidelity reproduction of an important
sound.
- Also,
certain sounds are masked by others, and if it is judged that a certain
sound would be masked anyway, why not give those bits to another sound which
would be heard?
This approach does not reduce the data size in order to reduce storage cost,
but primarily allows very selective and powerful noise reduction (i.e. more
accurate audio signals) than linear PCM at the same bit rates. Therefore the
quality of the audio signal rises at a constant bit rate.
Dolby Digital soundtracks can provide anything from mono to full 5.1-channel
surround sound. DVD- Video discs of movies can even carry multiple versions
of the soundtrack that differ in the number of channels. A disc might contain
a 5.1-channel sound mix with the dialogue in one language, a Dolby Surround-encoded
two-channel mix in another language, and a mono track with the directors’
comments or other supplementary information. The default soundtrack will vary
from disc to disc, so always check the DVD disc’s Language menu for
the choices offered.
All
Dolby Digital decoders, whether 5.1-channel or two-channel, have a unique
feature called "downmixing" that assures full compatibility with
any playback system. At your option, the decoder will create "on the
fly" from 5.1-channel programs a two-channel, Dolby Surround-encoded
mix for playback over a home theater system with Dolby Surround Pro Logic
decoding; a two-channel stereo mix for regular stereo and headphone playback;
or a mono mix for playback over a mono TV set.
Note:
downmixing is not used for laser discs because they contain three different
soundtracks: stereo PCM for a conventional stereo or Dolby Surround mix; one
FM track for a mono mix; and one FM track for a 5.1-channel Dolby Digital
mix.
Dolby Digital EX
While
Dolby Digital can deliver fewer than 5.1 channels, to get more than 5.1, you
have to move up to a new format—Dolby Digital EX. EX adds a "surround
rear" channel in addition to the regular left and right surrounds.
This
rear channel is placed behind the listener/viewer, while the left and right
surrounds are placed to the sides. Note, however, that this surround channel
is matrixed, not discrete, so it's not overly directional.
There are actually two variations of Dolby Digital EX—the original 6.1-channel
format (with a single matrixed rear channel) and the newer 7.1-channel format
(with matrixed rear left and rear right channels). Neither format is widely
used as yet, although more and more mid- and high-end A/V receivers are coming
with 6.1 or 7.1 EX decoders instead of the older Dolby Digital 5.1 decoders.
By
the way, Dolby Digital EX is sometimes referred to as THX Surround EX, as
it has THX certification.
Digital Theater Systems (DTS)
 Digital
Theater Systems Digital Surround competes head-to-head with Dolby Digital
5.1 format. DTS is very similar to Dolby Digital in that it provides up to
5.1 surround sound like Dolby Digital and provides the same frequency levels
to each channel as Dolby Digital. But music enthusiasts argue that the 12:1
compression on Dolby Digital loses a little too much audio quality as compared
to less compressed (3:1) DTS format. Again, to be able to use DTS your receiver
must support it and your DVD player must be able to output it (look for a
DTS sticker), or your DVD player must have a built in DTS decoder and a receiver
that is labeled as being DTS ready.
DTS ES
 Like
Dolby Digital EX, DTS ES contains extra information for a rear-center channel
speaker (or two rear-center speakers playing in mono with 7.1 home theater
systems.
Depending
on how the sound was originally mastered and stored codec can work either
as matrix or discrete. In contrast, Dolby's competing EX codec can only handle
matrixed data and does not support a discrete 6th channel. DTS-ES is backward
compatible with standard DTS setups, so non-ES equipment or with ES enabled
equipment that lack the extra speaker connections, sound plays back in 5.1
as if it were standard DTS.
DTS NEO:6
 DTS
Neo 6 can be used with virtually any two-channel digital or analogue stereo
audio source. Neo:6, like Dolby's Pro-Logic IIx system, can take information
from older matrix-surround formats such as Dolby Pro-Logic and Dolby Stereo
Surround and convert the sound into 5.1 or 6.1 channel format.
It is also capable of adding a 6th (rear surround) channel to 5.1 channel
DTS audio. However, Dolby's own Pro-Logic IIx system is better suited to handling
the older Dolby formats.
Surround Sound Comparison
As we have provided
a quick description of how each format works, its time to wrap up…
Amongst this plethora of acronyms, there are only a few that are important
when purchasing a home theater system. Sonically speaking, a move towards
formats like 5.1 makes a lot of musical sense: a strong (rather than phantom)
centre image, deep bass and – most importantly – the ability to
define a 360-degree panoramic soundstage.
The surround channel in Dolby Surround and Dolby Pro Logic soundtracks is
often indistinct and always nondirectional; it sounds mushy, and has a fairly
narrow dynamic range.
By far Dolby Digital is the most widespread multi-channel decoding scheme
used today for DVDs. Further, Dolby Digital has also been chosen as the audio-encoding
standard for upcoming HDTV broadcasts. Make sure whatever receiver you get
has the ability to natively decode (without the use of an external decoder)
Dolby Digital. DTS is the second most used format, and it is cheap enough
to purchase equipment with DTS compatibility that it is worth getting.
Anyone buying an A/V receiver or a home-theater system that include both Dolby
Digital and DTS decoders won't be missing out on anything significant--at
least for the next couple of years. Such an A/V receiver has the capability
to automatically detect DVDs with DTS soundtracks. DTS ES and Dolby Digital
EX are the future of surround sound, provided you have set the room up correctly.
Another thing to note is that lossy encoders tend to sacrifice stereo information
at lower bitrates. Any deviation from the original recording could result
in unusual sounds from the center and surround channels.
If you don't want to buy a new set of surround sound speakers, but still want
to experience the effects designed into 5.1-channel audio, a virtual surround
system may be just the thing you're looking for. They are more compact, easier
to install and usually less expensive than 5.1 systems, with far less speaker-wire
clutter.
That said, the bottom line remains:
The format you choose mostly depends on the amount of money you are willing
to spend, equipment you already have and the level of performance you are
willing to accept.
Previous 1 2 3
Back
to DVD R Homepage from Discreet Surround Formats page
|
