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RE: 5.1 or 7.1?

Posted by David Aiken (A) on January 18, 2008 at 11:51:56

In Reply to: 5.1 or 7.1? posted by Skye on January 18, 2008 at 10:52:23:

Material with 7,1 channels is not common.

Standard DVD has, at best, 6.1 channels with Dolby EX and DTS ES. The Dolby EX method relies on a matrix encoding while the DTS tracks can be discrete. Only a relatively small proportion of discs have either. The 6th channel is doubled to produce 7.1 when there is a 7.1 system available

BluRay and HD DVD are capable of discrete 7.1 but I'm not aware of how many actually currently ship with 7.1 tracks. Most of the reviews I can recall seem to refer to 5.1 tracks.

I run a 6.1 system. The extra channel gives a very seamless surround on the best 6.1 track DVDs I've got and it's preferable to 5.1 but the difference is small rather than major and you don't get any extra information, just better localisation. Synthesising a 6th channel using Dolby ProLogic IIx or DTS Neo6 produces a subtler change and I can happily live with or without it.

The big practical problem with 7.1 is room size. The side surrounds, the 4th and 5th channels, are placed just behind the level of the listening position. The 6th and 7th channel speakers need to be placed behind the listening position and you probably need at least a good 6' or so between them and you to get the best effect. That means a bigger room than you need for 5.1. I've got my 6th channel about 5' behind me and it works but more space would definitely be better, and that's true for all speakers in my setup.

If you don't have the room size to fit the speakers in behind you, you're better off with good 5.1.

If you've got 2 unused channels of amplification in your AVR, some receivers allow you to use them for bi-amping the front L and R speakers which may improve their sound slightly, especially for 2 channel music.

So 7.1 can certainly make a difference but it's not going to be a great one, there's only 6.1 rather than discrete 7.1 soundtracks available on standard DVD and only DTS provides a discrete 6.1 soundtrack there, probably limited availability of discrete 7.1 on the hi-def disc formats at this stage, and you need more space to get the most benefit from a 7.1 system and many people won't have that space. Hardly a compelling change to make but it does offer benefits if you do it. My feeling with 6.1 in my standard def system is that while I like what it has to offer, there's certainly not enough standard DVDs around with 6.1 soundtracks to make it a really cost effective upgrade.




David Aiken

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