Dolby Pro Logic IIz - What You Need To Know

Add Height To Your Surround Sound Experience

Dolby Pro Logic IIz Logo
Dolby Labs

Ever since Thomas Edison invented the phonograph in 1877, the quest has been on to make the reproduction of sound as real as the sound heard in its original environment. Today's surround sound technologies are just a continuation of this quest.

Dolby Pro Logic IIz: Surround Sound Goes Vertical

Dolby Pro Logic IIz processing is an enhancement implemented in some home theater receivers that extend surround sound vertically and fills the space above and in front of the listener.

Dolby Prologic IIz offers the option of adding two more front speakers placed above the left and right main speakers. This feature adds a "vertical" or overhead component to the surround sound field (great for rain, helicopter, plane flyover effects). Dolby Prologic IIz can be added to either a 5.1/5.2 channel or 7.1/7.2 channel setup. It is also compatible with two-channel and multi-channel surround sound sources, including, if applied correctly, Dolby TrueHD and DTS-HD Master Audio.

When added to a 7.1 or 7.2 channel setup, you end up with both surround back and front height speakers - However, you would then need amplification for all 9 channels. Since some home theater receiver only provides amplification options for 7.1/7.2 channels, you must forgo the surround back channel option when using the Pro Logic IIz feature when using a 7.1/7.2 channel home theater receiver. This means that you are actually using a 5.1/5.2 channel setup and adding the Dolby Pro Logic IIz height channels to obtain a 7.1/7.2 channel setup.

In order to use Dolby Pro Logic IIz to is the maximum effect, the front height speakers should be mounted approximately 3ft directly above the front left and right main speakers. In addition, to retain the character of the original surround sound mix, the speaker level settings for the height channels should be set slightly lower than that of the main left and right front speakers.

However, you tailor the speaker levels to your preference.

The Motivation Behind Dolby Pro Logic IIz

The motivation that guided the development of Dolby Pro Logic IIz is the observation that humans hear more from the front, above, and sides than from the rear.

In other words, in the effort to create an optimum surround sound listening experience, it is more advantageous to emphasize sound coming from the front, sides, and above the listener than it is to add more emphasis from sounds originating from the back of the listener.

In the case of current surround sound technology, the observation is that the traditional 5.1 channel surround schemes now commonly employed provide enough rear audio information for the listener, and adding one or two more surround back channels, as is promoted with current 7.1 channel home theater receivers, really doesn't give the listener that much more of a surround sound experience. In addition, in smaller room environments, adding one or two surround back channels is physically impractical.

For more details about the implementation of Dolby Pro Logic IIz, check out the official Dolby Prologic IIz page.

Pronunciation: Dolby Pro Logic Two Zee

Also Known As: Dolby Pro Logic IIz

Alternate Spellings: Dolby Prologic IIz, Dolby Pro-logic IIz

Related Technologies to Dolby Pro Logic IIz

Although the familiar Dolby brand name garners attention to Dolby Pro Logic IIz amongst consumers, there are similar technologies from Dolby and other companies that provide a similar listening experience.

  • Yamaha Presence: Yamaha offers a similar technology on some of its home theater receivers called Presence. This surround sound scheme also employs the addition of two front height speakers to add a full surround experience from the front and above the listening position.
  • Audyssey DSX: Audyssey, a company well-known for its speaker setup, room correction, and sound processing software, offers DSX (Dynamic Surround Expansion). like Dolby Pro Logic IIz and Yamaha Presence, DSX adds front vertical-height speakers, but, in a twist, it also provides for left/right wide speakers positioned between the front left and right and surrounds left and right speakers.
  • DTS Neo:X: In a similar fashion as the Dolby's ProLogic IIz surround sound format, which provides both height channel enhancement, DTS offers an 11.1 channel surround sound format that they have labeled DTS Neo:X. DTS Neo:X is designed to look for cues already present in stereo, 5.1 or 7.1 channel soundtracks and places those cues within front height and wide channels that are distributed to added front height and rear height speakers, enabling a more enveloping "3D" sound listening environment. To dig deeper into DTS Neo:X, refer to our article: DTS Neo:X - What It Is and How It Works.
  • Dolby Atmos: The concept of adding vertical height to the surround sound experience takes another leap. Whereas Dolby Pro-Logic IIz just adds vertical height to existing 5.1 or 7.1 channel content (and only to the front sound field), Dolby Atmos is an encoding/decoding system at allows vertical height sound components to be placed in multiple locations within a soundtrack during the recording and mixing process. For more details, read our article: Dolby Atmos - From The Cinema To Your Home Theater.
  • DTS:X: DTS:X has also come up with an immersive, object-based surround sound format that is a competitor to Dolby Atmos. For more details, read my article: An Overview of the DTS:X Surround Sound Format.
  • DTS Virtual:X: DTS Virtual:X is an interesting surround sound processing format in that actually projects a height/overhead soundfield without the need to add extra speakers. Instead, using complex algorithms, it fools your ears into hearing height, overhead, and even rear surround sound depending on how it is implemented in a sound bar or home theater receiver. For more details, refer to our article: DTS Virtual:X Surround Sound - What You Need To Know
  • AURO 3D Audio: Auro 3D is a channel-based surround sound system in which sound can be recorded, mixed, and reproduced in three layers. First, there is a traditional 5.1 channel layer, Next, a 5 channel height layer (placed slightly above the listening position) is added, and finally, there is a single top-layer (referred to as VOG or the "Voice of God"). In addition to home theater set-ups, this system can be adapted for headphone or in-car use. For more details, refer to our Overview of the Auro 3D Audio Surround Sound Format.

The Bottom Line

You are probably asking yourself, "Is my current home theater receiver obsolete if it doesn't offer any of these technologies?". The short answer is "NO". If you have a 5.1 channel system, good speakers and good speaker placement go a long way to providing a good surround sound experience.

I wouldn't replace a home theater receiver just to get the ability to add two more front or side speakers. Other things, such the ability to perform Dolby TrueHD/DTS-HD Master Audio decoding and HDMI connectivity would be a more logical reason to upgrade. However, if the receiver you are considering also has Dolby Pro Logic IIz or any of the other technologies mentioned above, that is definitely an added bonus, provided you commit for any added speaker layout requirements.

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