We throw around terms like Dolby Pro Logic and Matrix Decoding all the time. In today's show we actually define the terms, give a little background on the technology and hopefully explain it a bit.
Matrix Decoding
If you have even a mild interest in home theater you have heard terms like Pro Logic,
Dolby
Surround Stereo or even Matrix processing. Today we present a highly
simplified discussion on the process your receiver goes through to play
surround sound in your home theater. For a detailed discussion, the
Dolby website has many resources that get much more technical than we
can here (
Dolby Technical Library).
Pro
Logic, Dolby Surround Stereo and Matrix processing all refer to a
method for obtaining multi track audio from a single stereo pair. Let's
define some terms. Dolby Surround Stereo refers to the technology
developed by Dolby Laboratories for the cinema in 1975. In 1986 the
technology was introduced into the home market and called Dolby
Surround. Today the term is still used to describe the encoding process
by the studios. Dolby Stereo was eventually replaced with Pro Logic
which refers to the decoding technology used in the receiver to play
back material encoded in Dolby Stereo. Matrix decoding is the generic
term used for the process of encoding and decoding the two channel
audio into four.
The way Dolby Stereo
(Pro Logic) matrix processing works is that information for all four
channels (L/C/R/S) is encoded as a stereo signal. A processor (decoder)
is required to pick apart the information and route it to the
appropriate channels. The processor looks at phase and amplitude of the
incoming signals and then looks in a matrix for instructions on how to
route the information. In addition to routing the signals to the
appropriate channels the processor will also process the signal to
eliminate noise and adjust the audio levels. If the Dolby Stereo signal
is sent to a stereo receiver without Pro Logic decoding, the audio is
played back in regular two channel stereo sound.
What happens when you take regular stereo music and run that through a Pro
Logic receiver? Most likely it will produce
undesirable performance, with an
overabundance of the music mix focused through the center channel. The
introduction of Dolby Pro Logic II addressed this issue, providing 5 independent
channels of full range audio with separate modes for 2 channel
music and movie reproduction.
Dolby
Pro logic II takes any two channel source and matrix decodes it to 5
independent playback channels. It is fully compatible with Dolby Stereo
encoding utilized in broadcast. Some broadcasters encode their content
in Dolby Pro Logic II which enables them to deliver a 5 channel
listening experience via standard stereo analog broadcasts. Dolby Pro
Logic IIx, introduced four years ago, expands any stereo, 5.1 or 6.1
signal into a 6.1 or 7.1 channel listening experience. 7.1 is achieved
through the use of 4 independent surround speakers (left surround, left
back, right back, right surround).
For completeness we want to talk
about Dolby Digital and how it differs from matrix decoding. With Dolby Digital,
or AC3, the audio for each channel is individually represented in a digital
stream of ones and zeros. The
Dolby Digital processor (or decoder) knows how
decode and un-compress the data before sending it on to the speakers. The
benefit of this is that the audio is fully discrete and
digital quality, especially the surround and center
speaker. In the case of
Dolby Pro Logic, the surround signal was mono and limited in frequency response.
Dolby Pro Logic II brought 5.1 channel performance and full range surround
speakers to matrix encoding and decoding.
For 6.1 digital sound tracks Dolby employed a matrix encoding
and decoding process (Dolby Digital Surround EX) developed first for
use in the cinema to encode center rear channel information into the
left and right surround channels. The development of DDEX filled in
what some felt was a gap between the left and right surround speakers,
creating a smoother more natural surround sound effect and
simultaneously allowing the listener to better identify surround
signals that were originating from directly behind the viewer. Although
the process uses matrix decoding it is doing so with a digital source
for a more accurate and better sound. Dolby Digital Surround EX encoded
content is 100% playback compatible with all 5.1 surround systems and
surround decoders To get the full impact of Dolby Digital Surround EX
encoding you will need a DDEX equipped AV receiver and either a 7.1 or
6.1 speaker configuration.
