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La Scena Musicale - Vol. 8, No. 1

How to Set Up your DVD-Video

by Geoff Martin / September 2, 2002

Version française...

Walk into any video rental store and you'll see that we're well on our way to DVD-Video completely replacing VHS video tapes. There are a number of reasons why we can consider this a good thing, including an improvement in apparent video quality and no degradation in the signal caused by the ravages of time. However, perhaps the most obvious improvement is that DVD-Video brings what is known as "discrete multichannel audio" (more commonly known as "surround sound") to the consumer. Where VHS tapes can support only two independent channels of audio which are, in theory, routed to two loudspeakers, DVD-Video supports six independent channels of audio (better known as "5.1 channels").

In the best of all possibilities, a DVD-Video player has five outputs which provide full frequency range signals that are sent to five loudspeakers -- the Left, Centre, Right, Left Surround and Right Surround (abbreviated L, C, R, LS and RS). A sixth output for Low Frequency Effects (the "LFE channel" also known as the .1 in 5.1) is connected to a subwoofer -- optimised to only produce low frequency material.

The location of these five loudspeakers around the listener is crucial to the correct presentation of the sound field recorded on the DVD-Video. There is an official recommendation that was developed by the International Telecommunications Union (ITU) which is the standard configuration used by professionals worldwide. This recommendation states that all loudspeakers should be the same distance from the listener, with specific angular locations as shown in the figure. Note that the surround loudspeakers are supposed to be located to the sides and slightly behind the listener -- not far in the rear as is typically seen in homes and stereo stores. Remember that these are "surround" loudspeakers - not "rear" loudspeakers. (Readers wishing to read the exact details of this standard should download the document BS.775-1 from www.itu.ch for a small fee.) The placement of the subwoofer is less critical -- one possibility is on the floor in a corner of your listening room. If you have a DVD-Player and fewer than five loudspeakers and a subwoofer, then you must configure your player for the appropriate loudspeaker configuration. In order to hear something approaching a reasonable facsimile of that which you ought to hear, you must "tell" your DVD-Video player how many loudspeakers you have. Almost all players provide the user with various modes of operation which correspond to different configurations of loudspeakers, providing what is known as "downmixing" capabilities (because you are mixing 5 channels down to a smaller number of loudspeakers).

For example, most of the dialogue in a movie is exclusively routed to the Centre loudspeaker. If you have only two loudspeakers, correctly connected to the Left and Right outputs, then you will hear very little speech in your movie, but a great deal of soundtrack music; therefore the player should play the Centre channel in your Left and Right loudspeakers. In addition, it should be smart enough to also include the Left Surround in the Left loudspeaker and the Right Surround in the Right.

In a worst-case scenario, if you have a single loudspeaker, then the player should be routing all five channels to one output.

Every player has a different trademarked name on its particular method of downmixing for your loudspeaker configuration. The three important things to remember are

  1. your player doesn't know how many loudspeakers you own
  2. use the mode that's appropriate to your setup, and
  3. read the manual that came with the player. This will tell you the correct mode and loudspeaker placement for your system.

In the next issue, how five channels of audio can be squeezed onto a DVD-Video.

Version française...

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