Understanding
The Concepts of Sound systems
You must have heard the terms like AC3, DTS, THX,
etc. But what do they mean.
If you have visited a movie theater recently, you
will definitely noticed the little animation before the
movie that says you're going to be hearing is in Dolby
Digital (also known as AC3) or it may say its a THX
certified or even says its DTS.
So really, what are these terms?
DOLBY
DIGITAL
Dolby
Digital is technology that makes it possible to transmit
high quality sound much more efficiently than was
possible before. It was first used in movie theaters in
1992.
This technology divides the complete audio
spectrum of each channel into frequency bands based upon
frequencies that are optimized for human hearing. This
division makes it possible to filter & reduce the
noise when no audio is available & masks it at other
times by accentuating the stronger signals. Doing this
preserves the sound quality of the original signal, thus
letting Dolby Digital get away with capturing fewer bits
(around 448kbit/sec or 384kbit/sec) to describe the
audio.
It distributes the audio bits among the various
channels, this lets the strong sounds from one channel
provide masking for noise in the other. Using this
effective combination of masking & efficient
distribution of bits among the channels - Dolby Digital
can transmit more data, which is essential for good
audio quality in surround sound applications.
When it comes to theater prints,
Dolby Digital - is written in two tracks on film.
This two tracks are then read by Dolby Digital processor
present in the theaters, which converts them in to
surround sound at the time of play back.
DOLBY DIGITAL FOR HOME USERS
Now
a day almost every current player is configured with
Dolby Digital support. These players have a built in
Dolby Digital Decoder system which is also known as Down
Mixing Decoders which provide conventional analog stereo
outputs to surround sound.
Down
Mixing Decoders is the process whereby software &
hardware devices allow for the listening of
multi-channel material even when the necessary hardware
isn't available.
Understanding
the channel sound systems
What do 2.0, 4.0, 5.0, 5.1 and 6.1 in
a speaker system refer to?
These
signify the number of discrete audio channels that you
can use. For example, '2.0' is basic stereo, '5.0' would
be Dolby Digital and the '.1' adds the Low Frequency
Effects (LFE) channel-the woofers or sub-woofers that
produce lower frequency sounds to give that extra punch
to your sound.
Generally,
the first number indicates the number of satellites-the
small speakers that you place around your room-and the
second indicates whether an LFE speaker is included.
LFE covers about one-tenth the audible bandwidth
in comparison to the other speaker. This '.1' takes care
of all the BASS effects of the sound.
5.1 channel includes left, right, center, left
surround, right surround & ofcource LFE i.e. (.1).
DTS (Digital Theater System)
Launched
in 1993, DTS is another format capable of 5.1 surround
sound. Like Dolby Digital this format is a perceptual
audio encoding scheme that exploits the basic
characteristics of human hearing.
Almost all other concept in DTS are very similar
to that of Dolby Digital except the way it encodes the
signals. Speaking of encoding, DTS uses higher data
rates of 745 kbits/sec or 1.5 Mbits/sec which is almost
2 to 4 times higher than Dolby
Digital
to encode its 5.1 channels of surround sound
information.
Another difference in DTS is - Unlike Dolby Digital
the DTS sound tracks in theater release are not
contained on the film in its two optical tracks. The six
track digital sound track is stored separately on CD-ROM
discs, which are then read by a playback unit in
synchronization with the film.
DTS
films contains a special time code track essential to
the synchronization of the sound tracks to the film. Now
since each frame of the film contains the DTS time code,
the audio will always play the right background sounds
irrespective of cuts & breaks.
Standardizing
Audio Quality with THX
THX
is a sound certification standard has created guild
lines, which ensure that movies look & sound exactly
like the director intends it. To obtain this THX
certification, it has to conform to a number of rules
& regulations that also include physical parameters
such as the blocking of noises from outside the
screening area, poor sound quality, viewing angles,
etc.
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