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View Full Version : Confusion with Surround Sound formats...

Integrity
04-06-2005, 09:11 PM
I didn't know where to put this thread but when I searched for surround sound all of them originated from here.

Basically I am very confused with specifically the Dolby Surround format. I have read many websites and articles on the Internet that all explain it and Dolby's other formats...I am mainly confused on what is truly "discrete" (as almost all the website's put it) channels and what is "matrixed" channels. From the dictionary and my own experience with creating simple filters in Photoshop, I know a matrix is a rectangular grid used in an algorithm...and in another definition quite simply meaning a value derived, or is developed from another set of values (which is where the filter would come in; for one example in averaging surrounding pixels to create a blur).

But some websites will say that Dolby Surround is a 2 channel format which creates the additional Center and Surround channel by matrixing (hope I'm using that correctly) them from the Left and Right channels. But then another website will say that all four channels are discrete, seperataly stored channels that are independent on their own which are encoded into the Left and Right.

This is where my confusion comes from, and I was wondering what the truth was. I tried to go to Dolby's website to see if they basically put it in simple English but for some reason the website won't establish with my computer (I have been having problems lately).

This is what I have set in my mind from averaging out all the websites that I have read...if I am wrong please correct me as this is the reason of my post...

Dolby Stereo refers to their Left, Center, Right, and Surround channel format. At first I thought it was their 2 channel format but I knew stereo did not mean only two channels but rather multiple channel setups which the articles thus proved.

Dolby Surround refers to Left, Right, and Surround...but the Surround channel is where my braindead symptom comes from. Like I said before some websites say it is a discrete channel encoded in the Left and Right (rather what they called Left Total and Right Total), and others say it is matrixed from the Left and Right through phase shifting and/or subtracting either the Left/Right from the Right/Left deriving the Surround through the result.

Dolby Pro Logic refers to Dolby Surround but with an added Center channel which is created through mixing the Left and Right to create a "phantom" center. Other website's would also then delimit my thought by saying Dolby Surround was LCRS and Pro Logic was just the decoder that decoded the Center and Surround channels.

Dolby Pro Logic II refers to Pro Logic but with two seperate Surrounds. Again some saying the Surrounds were just a slightly more complicated phase shift creating a stereo image but still being derived off of the mono signal from the difference of the Left and Right channels. Then other sites saying they were discrete.

Dolby Digital 1.0-5.1 refers to 1-6 discrete channels. This one never confused me because all of them clearly said discrete.

I guess the main question is if those respective formats that confuse me really have discrete Surround and Center channels or if they are created or "simulated" from the difference of the Left and Right/phase shifting for the Surround, and mixing Left and Right for Center.

I was testing this the other day on my 5.1 speakers with my Dell and an Audigy 2, using CyberLink DVD. I made sure the 6 speaker output (rather 5.1) was selected along with the Pro Logic decoder setting left on when I would select the respective track. I selected the Dolby Digital 5.1 track and all went well...amazing in all its glory (the DVD I was watching was Anastasia at the part when she sings the Once Upon a December song); being able to select the volume of each individual speaker was interesting to see how they mixed it. When I selected the Dolby Surround track, and then only having the rear speakers on to see how the Surround channel sounded, it played back a somewhat reverberated form of the music and her singing. Now knowing that they added a reverb for acoustic purposes to the music...and knowing that that reverb added a more stereo image...it sounded like it was a derived channel from the Left and Right and not a true discrete channel because I have messed around with subtracting reverberated samples before and this is exactly what I got (due to the reverb adding random phase shifting and echoing and what not, like when you want to change a mono signal into a stereo one).

Basically in the end I just wanted to know is if they are not discrete channels...and if they are not then am I right saying that all 2 Channel signal's can be made into Dolby's Surround format through their processing? I basically wanted to create a Surround format for some of my 3D stuff.

I hope I explained all of this clearly.

Thank you.
imashination
04-06-2005, 10:02 PM
am I right saying that all 2 Channel signal's can be made into Dolby's Surround format through their processing? I basically wanted to create a Surround format for some of my 3D stuff.

Because im lazy, Ill skip the small book you wrote previously to this last sentence ;-)

There is Dolby digital, which is surround sound, containing 6 individual (discrete) audio channels

Then there are the prologic systems, where they are using existing/cheap broadcasting methods to get a kind of surround sound signal using just 2 audio channels. By mixing, limiting and combining them correctly, they can do all sorts of effects. For example filtering a plane engine noise to a certain frequency, the pro-logic system will filter it out to the back. These are not discrete channels, they are not properly seperated out to the 100% correct speaker locations and will each lack certain frequencies.

Now as for 3D, you need ideally a software that has some sort of surround sound feature built in, otherwise youll just be mixing it manually afterwards. I only know first hand that c4d will offer you the ability to output 5.1 and 7.1 discrete audio channels, but youll require some software to encode this signal from the individual files.
Integrity
04-06-2005, 10:16 PM
Sorry about the long post, I just felt that I should fully explain my situation so people would understand where I'm coming from.

Thank you...you basically closed the door and helped me. So I should now know from your reply that Dolby Surround is the format used in theaters, that do have discrete channels written upon the film...and the Pro Logics are just a cheap consumer level way of making a 2 channel waveform into a surround sound source; thus not making the Surround and Center channels discrete.

Which means any 2 channel soundtrack I create for my 3D and movie stuff could be properly called Dolby Pro Logic I/II or Dolby Digital 2.0?

Thank you.
imashination
04-07-2005, 06:05 PM
Which means any 2 channel soundtrack I create for my 3D and movie stuff could be properly called Dolby Pro Logic I/II or Dolby Digital 2.0?

Just by having a 2 channel audio output does not mean you can label your output as prologic. You still need to edit the audio in a surround sound format and then use a prologic encoder to reduce it down to two non-discrete channels.
Integrity
04-07-2005, 08:23 PM
I forgot to say that I would encode with an AC3 encoder...what I meant to say that when I do encode it down to 2 channels is if it could be called Pro Logic.

There have only been two formats from Dolby for DVD's that I have seen being used. Dolby Surround and Dolby Digital 1.0-5.1. Some DVD's will say Dolby 5.1 Surround which I assumed was their digital format. I never ever see a Pro Logic and since you said the channels are not discrete then all of that makes sense. Which would lead me to say that when they say Dolby Surround it is actually a 2 channel, am I correct to say that all a Pro Logic encoder does is mix the Center and Surround with the Left and Right? Which is then where I got assuming that creating a 2 channel format could be simulated into a Surround. And if that's the case then couldn't a Dolby Digital 2.0 soundtrack be called Pro Logic or technically the Pro Logic turning into a Surround?

My thing is that you said if you want Pro Logic then you have to still create a Surround for the soundtrack...but if all the Pro Logic does is take the 2 channel image and create a Surround and Center from it...does it really matter whether or not you create a Surround for it...because it would just get mixed back into the 2 channel? It's like (if the thing about Pro Logic turning Dolby Digital 2.0 into Surround is true) I could create a Surround track, but when I'm done just mix it in my own complicated way into the Left and Right and then encode it with Dolby Digital 2.0 instead of having to have a Pro Logic encoder.
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