In various articles we have already paid attention to the different surround formats that we currently find on Blu-ray discs, DVDs and receivers. Two well-known new surround formats are Dolby TrueHD and DTS-HD Master Audio . However, Dolby still has a surround format that has been used for a number of years; Dolby Pro Logic. But what exactly is it?
This format of Dolby is an audio processing technology from Dolby Laboratories that makes it possible to extract multi-channel audio from a stereo source or a source with a Dolby Surround soundtrack. The technology is therefore mainly found on AV receivers and all-in-one home cinema systems, since the incoming audio signal can be converted to a multi-channel surround signal. The signal for the surround speakers is filtered from the stereo or Dolby Surround signal, without adding extra elements. At the time of writing, there are four different Dolby techniques.
Dolby Pro Logic
Dolby Pro Logic is the very first version developed by Dolby and makes it possible to extract a 4.0 surround signal from a stereo source or a source with a Dolby Surround soundtrack. These 4 channels are the two stereo speakers at the front, the center speaker and a mono channel for the speaker (s) at the rear. This was already a big step at the time of the introduction, but we can now expect at least 5.1-channel surround sound.
Dolby Pro Logic II
This was introduced for 5.1 channel surround sound. This is an enhanced version of Dolby Pro Logic that allows 5.1 channel surround sound to be obtained from a high quality stereo source or source with Dolby Surround. For example, two speakers at the front, a center speaker, two speakers at the back and a subwoofer can be provided with its own signal.
Dolby Pro Logic IIx
Although a 5.1-channel surround sound is more than enough for most people, more and more home cinema systems are equipped with 7 speakers and a subwoofer, in short, a 7.1-channel speaker system. Dolby is now also responding to this with Logic IIx. This technique makes it possible to convert a stereo signal, a source with Dolby Surround or a source with Dolby Digital 5.1 surround sound to a 6.1 or 7.1-channel surround sound.
Dolby Pro Logic IIz
The most recent Dolby Pro technology is Dolby Pro Logic IIz. This makes it possible to add so-called height or width channels to your home cinema system. Pro Logic IIz sends additional surround information to two effect speakers placed above the two speakers located at the front. For example, a 5.1-channel system can be expanded to a 7.1-channel system and a 7.1-channel system can be expanded to a 9.1-channel system. These extra channels are mainly intended to intensify environmental effects such as wind and rain. The principle for the technique remains the same; the information is taken from a standard stereo, 5.1-channel or 7.1-channel source.
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