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A Discussion on Surround Sound Systems

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Old 07-30-2005, 07:04 PM   #1  
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Default A Discussion on Surround Sound Systems

Letís Talk Surround
This is a page I added to the www.highdefinitionblog.com and thought it should be repeated here as well.

A Bit of History
With the movie industry continually trying to entice more people into the theaters, you would expect that surround sound would be another weapon in their arsenal and indeed it was. Surround sound in the movies started back in 1941 with the movie Fantasia put out by Walt Disney. Only two movie houses put in the equipment which cost in excess of $80,000, so it was some time before surround sound at the movies became mainstream. This early system required synchronizing two projectors; one for the film and the other for the sound. It was a four channel audio system.

Later a magnetic media based surround system became popular for a while which could deliver up to 6 channels of audio. The problem with these early systems is they needed to be synchronized with the film projector and they were very troublesome to operate. They also applied magnetic strips to the film, but the cost of these films were about 10 times that of optical tracks. Additionally the optical tracks allowed for universality as the films could be played all over the world.

The Big Breakthrough
Then in 1966 Dolby Labs came out with a breakthrough in sound processing, the Dolby A-type noise reduction system. This would finally allow the optical audio on films to carry a stereo sound track. This was huge as it allowed movies to be shown on a single machine with a two channel (stereo) soundtrack. Soon thereafter the Dolby stereo system became a major breakthrough in movies with surround soundtracks. Using a process called Matrixing, Dolby encodes the stereo soundtracks with four channels of information. At first the Dolby Surround was three channels and did not have the center channel. Later the Dolby Pro-Logic include a fourth channel as shown in the following figure.


As shown there are four discrete channels:
1. Left
2. Center
3. Right
4. Surround
5. Optional LFE channel
The left and right channels contain all of the four channels and are decoded by a Pro Logic decoder. When there are sounds which are of equal volume and phase in the two channels the decoder will divert those sounds to the center channel. Primarily this will be voices that are centered in the picture. To create the surround channel the surround sounds are recorded at equal levels, but 180 degrees out of phase with each other, thus allowing the decoder to divert the sounds recorded in such a manner to the surround channel. Also the decoder had to send signals to the appropriate channels at the appropriate levels for when the sound origin was in between the left-center-right. The positional accuracy depended a lot on the quality of the mix on the film as well as the quality of the playback decoder, and while was very good in the theaters, was not so good in some of the early Pro-Logic home systems and the front positioning would actually be better without the center channel on many films. Other issues that limited Pro-Logic are numerous, but the overall effect was a leap and a jump over stereo and could be easily recorded on VHS prerecorded movies.

One such problem that the four channel matrixed system had in addition to the positioning at the front of the movie was the fact that only a single surround channel could be encoded. Therefore it was best used for non-positional sounds like the noise of a crowd, thunder, ocean noise, etc. If, for example, the director wanted to have the sound of a train traverse from one side to the other at the rear of the theater, the Pro-Logic system could not accomplish that task. Another problem is that many home processors will pop and hiss due to a weird combination of frequencies that could confuse the decoder. This would result in a surround pop when an actor said a word that started with a hard P sound.

The LFE channel was simply a crossover of the low frequencies that were in phase and sent to a separate subwoofer amplifier and speaker.

The Digital Era Arrives.
With the advancements made in the digital technologies, the first Dolby digital format (AC-1) arrived in 1984 followed by the AC-2 improvement. Dolby Digital (AC3) arrived in the cinema in 1992 which featured five channels plus a LFE channel:
1. Left
2. Center
3. Right
4. Left Surround
5. Right surround
6. LFE
While Dolby called this AC-3, it is commonly called 5.1 also. The improvement over Pro-Logic is more than just the additional channel. Now with each channel being discrete, the limitations of matrixing are eliminated. Now trains could indeed travel across the rear of the theater, or at least side to side. The surround channels, left and right, are again well suited for sounds that are somewhat non-positional sounds like the noise of a crowd, thunder, ocean noise, etc, but with the two discrete surround channels much better effects can be achieved, such as a bird chirping only in the left surround channel. It is still not intended for rear imaging, which is why they are called surround channels rather than rear channels. In the future the 7.1 systems may add the three rear channels which would be required for rear sound positioning. Still, even with just surround being discrete right and left as opposed to the Pro-Logic, the crowd noises at a sporting event can sound much more realistic with separate left and right surround channels.

6.1 and 7.1 Systems.

The 6.1 system is a product of Digital Theater Systems, Inc. (DTS) who develops surround systems the same as Dolby. With a DTS 6.1 ES (Extended Surround) there is a center rear surround channel added. It can be matrixed, which is decoded from the left and right surround channels or a separate discrete channel which is encoded on the DVD. Even when there is a discrete rear surround channel the same information is matrixed in the left and right surround channels for compatibility with 5.1 systems. Equipment that have a 6.1 decoder will subtract the rear surround information from the left and right surround channels to restore them to discrete channels. The 6.1 systems you can currently buy will develop the center surround channel in much the same way as the Pro-Logic systems developed the front center channel when the discrete rear surround channel is not present. Since the source is digital, the decoder can be much more precise. Since there is naturally occurring matrixed information in Dolby 5.1 encoded DVDs, quite often the decoder will supply information to the rear surround channel, thus improving even 5.1 encoded discs.

Currently there are not any sources for 7.1 systems, although it is expected to be the next generation of theater sound. The 7.1 systems will have left and right surround channels as well as left and right rear channels and the rear center channel. Again the systems available today will just develop these additional channels from the 5.1 channels of the source.
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Last edited by rbinck; 08-02-2005 at 02:32 PM.. Reason: Clarified the 6.1 and 7.1 information
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Old 07-30-2005, 08:05 PM   #2  
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Quote:
Originally Posted by rbinck
Letís Talk Surround
With so much focus on the video portion of home theater, the audio portion seems to get left out. But going from regular stereo sound out of your tv to 5.1 or better Dolby is almost (but not quite) as dramatic as the jump from SD to HD. I love it, and I wonder what percentage of people in this Forum use a receiver with surround sound to maximize the home viewing/listening experience???
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Old 07-30-2005, 08:13 PM   #3  
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man are you out of date, i have a 6.1 system,and there a lot of films in 6.1 and some films are listed as 5.1 but will decode as 6.1. in fact with hdvd and blu-ray coming soon those players will have dolby digital + up to 13.1!!! man get up to date!!
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Old 07-30-2005, 08:34 PM   #4  
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Quote:
Originally Posted by tvine2000
man are you out of date, i have a 6.1 system,and there a lot of films in 6.1 and some films are listed as 5.1 but will decode as 6.1. in fact with hdvd and blu-ray coming soon those players will have dolby digital + up to 13.1!!! man get up to date!!
Who's out of date? Rbinck? I don't think so. Actually, I think anything over 5.1 is overkill. My Denon receiver will handle 6.1 but I chose not to bother with the center rear channel. I think 2 in the back is just fine, but that's just my personal opinion. I doubt many others go to the extreme of 7.1 , and I can't even imagine 13.1 because at some point it just doesn't seem like you could notice the incremental difference. Maybe if I heard it I'd think differently, but I can't imagine the impact of those extra 8 channels being more significant than going from stero to 5.1 (just IMHO).....
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Old 07-30-2005, 09:02 PM   #5  
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Don't just throw bombs! Tell us details and furnish links. Many decode to 6.1 because the receivers are doing the work as explained. I don't mean to call your baby ugly, but I don't know of any discrete 6.1 or 7.1 sourced DVDs. If you do give us a link and I will update. I know the standard exists for the extra track.

There are several DTS 6.1 ES which are matrixed. The Lord of the Rings being one I can think of off hand.

Edit:
Cat if you have an old Pro-Logic surround amp laying around, you can feed the left and right surround signals from your 5.1 system to let the Pro-Logic amp develop the center rear channel. It is not as good as the 6.1 systems because it is analog decoding vs digital, but it does sound pretty good.

Last edited by rbinck; 07-30-2005 at 09:44 PM..
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Old 07-31-2005, 11:19 AM   #6  
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Thanks for the information, rbinck. I am in the process of setting up surround (or maybe non-surround in my case) for my Pan. 50LC14. I have an old Sony Pro Logic STR DE-405, and yep, the manual says the rear speakers are mono.

The room I'm putting it in has no way to connect the rear channel (cath. ceiling, fireplace on one side and open space on the other) unless I want to go wireless - hardly seems worthwhile for a mono rear. I might not even use a center channel as the receiver has a "phantom" center channel which seemed to sound pretty good when tested. I am using Bose 301 series II speakers and they didn't seem very compatible with a couple of center channel speakers I tried.

I actually like the sound from the TV (don't laugh!), except for the lack of deep bass. I'm not sure whether it's worth it for the hassle of yet another component and remote. I also need to connect it so that It will default to tv sound. I am using a Pace dc550p HD box. Anyone have any comments or suggestions - other than buying a new 5.1 system?

Cheers!
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Old 07-31-2005, 01:54 PM   #7  
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Surround, it should be noted is an effects channel. It should not be confused with a four channel system intended to place sounds anywhere in the room. The standard placement of surround speakers is on the side walls at your seating position, not behind you. That is why they are called surround as opposed to the rear. There can be a center channel placed in the rear center and left and right rear speakers placed behind you as well in the 7.1 systems. These channels will most likely be matrixed as opposed to discrete. After all the movie producers want your attention primarily ccentered on the screen not what is sneaking up behind you.

Now it does seem that there are some DVDs that are encoded with a discrete center rear channel. I found a list at http://www.dvdtherapy.com/dts_list.php, so it seems as though tvine2000 had a point in post #2. I'm not sure it was a life and death thing or anything like that, like the tone of that post seemed to be, but maybe tvine has spent too much time on other forums where the standard practice seems to be playing gotcha.

Last edited by rbinck; 07-31-2005 at 01:58 PM..
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Old 07-31-2005, 03:12 PM   #8  
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Thanks for the insight Rbinck, as usual, you intimidate me with your knowledge. I did a little tinkering with my 2 sound systems. My computer has an older Hercules 7.1 (which I love) sound card in it. I also have a cheap set of Creative 6.1 speakers. I played the movie "21 Grams" and did notice a "little" enhancement to the sound quality of the movie due to the rear center. I then played it in my home system (Aiwa receiver 5.1 + dts - jensen center, sub & rears with jbl pro-monitors up front). I then asked the wife and son to watch the movie on both systems (without telling them what I was doing) but asked them to pay particular attention to the sound. They both concurred that they could not tell a difference (other than the obvious jbl pro-monitors). I then told them what I was doing and they listened again - with conflicting opinion. My son thought the 6.1 was an added bonus when my wife vehemently said that the rear center was a distraction. In conclusion - I started a fight at Oblioman central.
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Old 07-31-2005, 06:30 PM   #9  
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Quote:
Originally Posted by rbinck
Cat if you have an old Pro-Logic surround amp laying around, you can feed the left and right surround signals from your 5.1 system to let the Pro-Logic amp develop the center rear channel. It is not as good as the 6.1 systems because it is analog decoding vs digital, but it does sound pretty good.
Thanks. As usual, you are way beyond me in your knowledge of this stuff. But nevertheless, I will try to post an intelligent reply. My Denon receiver does have 6.1 Dolby, but I don't use the "6th" channel. The main reason is that I had my living room pre-wired for 5.1 when the home was being built in 2002. All I had ever heard of at the time was 5.1 so I asked the builder to put in wiring for left and right rear channels. During 2003 after I had moved in, I was looking for a decent surround sound system, and the Denon receiver I found on sale just happened to be a 6.1 Dolby receiver. So I bought it, and rather than trying to run a new line for the center rear channel, I just set that channel to "OFF" and I don't use it. Honestly, I don't think I miss it either, because the 5.1 is really awesome. And that's part of the reason why I agree wholeheartedly with you and not that tvine2000 poster, because I can't imagine that 6.1 or 7.1 or even 13.1 could be all that much better. I think he needs to break the Prozacs in half next time.....
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Old 07-31-2005, 07:59 PM   #10  
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By setting the rear center surround channel to off, the information for that channel will be equal in both the left and the right surround channels. This will have the effect of "centering" that information between the left and right surround channels. Since the information is surround effects as opposed to the voices as it would be in the front, the necessity of having the physical speaker there is not as much as it is for the front center channel.

I'd guess you may only notice a small amount of difference, if any, by adding the 6th. speaker, so I guess I agree with you.

To me the only channel I wish they had they don't is a tactle LFE channel for the tactle transducers, like the Buttkickers. For me and my wife it is annoying to get the tactile vibrations with music and I think if it only came in with explosions and other things that would vibrate you it would be better. Not much of a chance that will happen though as they don't put tactile transducers in theaters much and that is the driving force for all of the surround technologies.

Last edited by rbinck; 07-31-2005 at 08:04 PM..
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Old 08-02-2005, 01:58 PM   #11  
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Default 5.1 System

My wife bought me a HK 5.1 receiver for Christmas. I don't think she knew what she was gettting me into. She just wanted to replace the old receiver from 1960. Now I've got the 5.1 setup and when its off and we just have the TV speakers on she thinks the TV alone sounds like crap. For those of you who have not tried 5.1 its awesome. I was watching Jurassic park last night and in one of the jungle scenes if I closed my eyes if sounded like I was in the middle of a rain storm. Now if I can just swing the $$ to get a 42 inch HD monitor to go with my sound system....
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Old 08-06-2005, 08:10 PM   #12  
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Quote:
Originally Posted by rr2465
My wife bought me a HK 5.1 receiver for Christmas. I don't think she knew what she was gettting me into. She just wanted to replace the old receiver from 1960. Now I've got the 5.1 setup and when its off and we just have the TV speakers on she thinks the TV alone sounds like crap. For those of you who have not tried 5.1 its awesome. I was watching Jurassic park last night and in one of the jungle scenes if I closed my eyes if sounded like I was in the middle of a rain storm. Now if I can just swing the $$ to get a 42 inch HD monitor to go with my sound system....
Christmas is coming. Maybe she's making a list, and checking it twice.... Be good!

But seriously, have you ever seen "Hulk" since you got the5.1 setup? It starts out slow, but about an hour into it there are some awesome sound effects. Can anyone recommend other "can't miss" movies with great audio to match the video?

p.s. If you're hoping for a plasma, ask Mrs. Clause for a 50" to get the true 720p HD effect without scaling the 1280 down to 1024. Plus it's a lot more square inches of "awsomeness" (almost 42% more)

Width Height Width Sq Height Sq Sum Sq Root (Diagonal) Area (WxH)

43.579 24.513 1899.129241 600.887169 2500.01641 50.0001641 1068

36.607 20.591 1340.072449 423.989281 1764.06173 42.00073487 754

Difference 314

Percent More 41.6446%

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Old 08-07-2005, 11:50 PM   #13  
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Gotta love Pearl Harbor DTS for the initial fly-by scenes of the Jap Zeroes. Later there are the .50cal guns behind you and to the sides while torpedoes are zinging from left to right and bullet ricochets all over the place. Will definately have you looking over your shoulder.
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Old 08-08-2005, 10:26 AM   #14  
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Quote:
Originally Posted by Blue_Tech
Gotta love Pearl Harbor DTS for the initial fly-by scenes of the Jap Zeroes. Later there are the .50cal guns behind you and to the sides while torpedoes are zinging from left to right and bullet ricochets all over the place. Will definately have you looking over your shoulder.
Thanks, that's exactly the reaction I'm looking for. I'm assuming the "Sub" (pardon the pun) will be quite active too if there are lots of explosions. I'll try that one, maybe this weekend. I guess I already know how that movie ends (good guys win), but how is the story line? Will I need the DTS to keep me awake, or is there some good writing and acting to go along with excellent sound effects?
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Old 08-08-2005, 09:26 PM   #15  
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Quote:
Originally Posted by CatManDoo
Thanks, that's exactly the reaction I'm looking for. I'm assuming the "Sub" (pardon the pun) will be quite active too if there are lots of explosions. I'll try that one, maybe this weekend. I guess I already know how that movie ends (good guys win), but how is the story line? Will I need the DTS to keep me awake, or is there some good writing and acting to go along with excellent sound effects?
Its got a decent sub plot (love story) to go along with the war story. It's very long at close to 3 hours but I've managed to watch it about 3 times this year, if that tells you anything.
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