Any way to tell if source audio is Pro Logic encoded?

[Michelle]

I'm reading a document from Dolby and they say that if the source is not Pro Logic encoded then you shouldn't encode AC3 with the surround flag. Is there a way to tell if source audio is Pro Logic encoded?

[bugster]

Good question.

Can you play it through a pro-logic decoder and see if the 'pro-logic' light comes on?

[Michelle]

On my receiver I select Pro Logic mode but it doesn't indicate whether the signal is actually Pro Logic.

[yoda313]

On my receiver I select Pro Logic mode but it doesn't indicate whether the signal is actually Pro Logic.

Hello,

Do you get decent surround in the rear speakers????

Remember pro logic is mono rear so it won't sound as crisp as dolby digital.

Also, try ripping a chapter from it to your pc. If it doesn't have a .1 it's possible pro logic. If its 2.0 there's still a chance it's pro logic.

Kevin

[Michelle]

The source is from tv not dvd. I haven't found listening to be a reliable indicator.

[yoda313]

The source is from tv not dvd. I haven't found listening to be a reliable indicator.

Hello,

What type of program was it???

If it was a movie chances are it was pro logic.

Is it standard tv or hd????

Kevin

EDIT - if it was a regular tv show watch the credits. Usually at the end of it there will be either a dolby double d symbol or it will explicitly say "DOLBY SURROUND". Now older shows may in fact be original dolby surround without a seperate center channel - just stereo front and mono rear. However most of the newer shows - 90's and newer - SHOULD be pro logic with stereo, center, and mono rear. Of course it seems like there isn't an easy way to be 100% sure if it was encoded in pro logic.

You do have a stereo vcr your recording on right?? Or if it's straight to a pc capture card via antennae/cable it WILL be stereo.

You know my sony digital amp has an auto format decode that automatically detects dolby digital signals. It however, DOESN'T switch over to pro logic if it REALLY IS PROLOGIC (even on commercial vhs tapes like Jurrassic Park that EXPLICITLY state PRO LOGIC).

[Michelle]

It's a regular tv show on standard tv. There is no mention in the credits. This show is Smallville and it's probably Pro Logic. But I would like to find a foolproof way of determing this, if that's possible.

Anyone know what the consequences are of using the surround flag when the source isn't Pro Logic?

[yoda313]

Hello,

If it's a brand new show I'd almost guarentee it's PRO LOGIC.

I can't imagine there'd be any consequences if you screw it up. Just use a rewritable disc so you can start over if it doesn't seem to work.

Kevin

[Kurt S]

They probably say that to save space. No sence in adding 4 channels if it's not needed

[yoda313]

They probably say that to save space. No sence in adding 4 channels if it's not needed

Hello,

PRO LOGIC is NOT 4 channel audio. At most it's 3 channel.

FRONT LEFT, Front Right, CENTER, MONO REAR.

It shows up as 2.0 digital on older dvds though.

Kevin

[Michelle]

They probably say that to save space. No sence in adding 4 channels if it's not needed

It just sets a flag. It doesn't change the number of channels.

[Heywould3]

the original poster is a bit confused.. dolby use to encode in prologic.. and that was 4 channel.. center front left front right and mono rear. some were 3 channel also but that was simulated... anyway.. the OP needs to know that Dolby proligic and DOlby digital are two different things Dolby Digital is sometimes refered to AC3 and if youre reciever has that.. it WILL ahve an indicator.. older prologic recievers had a settign for prologic but no indacator if it was encoded that way or not.. it not real easy to tell. BUT most older recievers had an internal processor that would simulate PL even if it wasnt encoded in the source. all vhs tapes will have the symbol on them if its encoded.. ALL dvds will have the Dolby ot DTS symbols or both.. no DVD will ever be encoded in PL.. it will have DD or DTS ..

[monzie]

I might be wrong here but isn't ProLogic an upsampler as opposed to any audio format?

IE. Prologic I or II takes a STEREO source and upsamples to a multi-chanel source?

[adam]

Correct monzie. Prologic is a DECODING method not an encoding method. Audio cannot be prologic, it can simply be decoded to prologic. So play a 2 channel audio source in stereo mode you get two channels. Play it with a prologic receiver and you get 4 channel surround and if you have prologic II support then you get additional simulated surround effects, but all with a 2 channel audio source. The additional surround channels are created through a matrix, basically just an algorithm that works in a very convincing way.

Unless there are stations out there broadcasting in mono, you will always be able to get Prologic at the very least from such broadcasts provided you have a prologic receiver.

[Heywould3]

hmm...
http://cnx.rice.edu/content/m10484/latest/

or here

http://www.5dot1.com/articles/pro_logic_vs_pro_logic_2.html

it actually is encoded PLII can upsample.. and as i said a PL reciever will also.. BUT as i also said its simulated.. i think its the wording.. but PL is from a 4 channel source placed in a "stereo" wraper then DE-Coded back into the 4 channel it was intended

[yoda313]

Hello,

I finally bumped into physical proof that Dolby 2.0 CAN be DOLBY SURROUND (IE Pro Logic):



There - Star Wars saves the day again!!!! This is STEREO with the Pro Logic flag on it.

Kevin

[adam]

Yoda, Dolby Surround is 2.0, but decoded to 4.0 on a Dolby Surround decoder...and any stereo signal is decoded to Prologic on a Prologic II decoder...but Dolby Surround and Prologic are two entirely different things.

Prologic is the successor to Dolby Surround and the whole point was to get to the point where you could simulate the surround effects from any stereo source regardless of how it was encoded.

[yoda313]

Yoda, Dolby Surround is 2.0, but decoded to 4.0 on a Dolby Surround decoder...and any stereo signal is decoded to Prologic on a Prologic II decoder...but Dolby Surround and Prologic are two entirely different things.

Prologic is the successor to Dolby Surround and the whole point was to get to the point where you could simulate the surround effects from any stereo source regardless of how it was encoded.

Hello,

I know that pro logic has the center channel whereas the older "surround" was just front stereo/mono rear. I was just showing 2.0 can be surround sound.

And to reiterate an early point 5.1 is FULLY compatible with PRO LOGIC as I played it through my Pro Logic receiver before I bought my digital a few years ago.

Kevin

(thanks for being so descripitive adam ).

[Nelson37]

I am fairly certain that Prologic I and II are in fact encoded into a stereo signal. I remember the discussion involving both out-of-phase and inverted signals muxed into a standard stereo signal, in such a way that standard amp would play normal stereo. Recording in normal stereo would preserve the Prologic encoding.

SFAIK, Prologic can be simulated from a normal stereo signal.

Prologic II does have seperate left rear and right rear channels.

Many TV programs may be PRODUCED with one audio format, and BROADCAST with something completely different. Insignia at end of film may not be significant.

It is apparently possible to capture a broadcast AC-3 signal.

[adam]

There is no such thing as Prologic encoding, and there is no such digital audio format called, "Prologic." Prologic uses the same matrix info as Dolby Surround, which IS an actual audio format. If you wanted to encode "for Prologic" you would make a "Dolby Surround" audio source. That's all I'm saying. Prologic is by definition only a decoding method, not a format or method of encoding.

And if you are talking about Prologic II then you don't need the matrix information at all, it will work on any stereo source though I would guess that a matrixed Dolby Surround source could give better results.

If you read Dolby's white papers on its Prologic formats it pretty much goes like this...

Dolby Surround supports: Dolby Surround sources
Prologic supports: Dolby Surround sources
Prologic II supports: any stereo source

I concede that I misspoke when I said Prologic would decode any stereo source, I was thinking Prologic II. Basically, if you've got a Prologic II decoder then you will always get at least Prologic from any source as long as its not mono.