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    Invelos Forums->DVD Profiler: Contribution Discussion Page: 1 2 3  Previous   Next
Determining 2 channel mono vs. 2 channel stereo
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DVD Profiler Desktop and Mobile Registrantmediadogg
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I think we are getting some (admittedly very confusing) things conflated.

1. The encoding and processing of the actual bit stream representing the audio that is sent to the speakers.
2. The encoding and processing of the bit streams that represent the metadata headers that describe the format of the contents.

I think they are almost entirely independent. The digital processing that creates, say Dolby, don't require any knowledge derived from metadata to know what to do.

And for another example, the process that creates ATMOS effects works regardless of whether the audio bit streams are coming from a disc or from the network.. All of the necessary content headers and metadata are encoded within the stream, to tell the codecs in the Xbox or A/V receiver what to do.

The metadata we have been talking about is different, albeit encoded in a complex bit stream on the DVD or BD, this data is not actually a part of the audio stream itself, and does not have any relevance to the actual codec processing - it is information for humans (and programs such as players) only.

Now that is the way I understand it to work. There may be other ways for it to work. If someone has actual technical knowledge or experience that would inform me better on this, it would be appreciated. Otherwise, any other reasonable conjecture would be just that - and I am pretty comfortable with my own, semi-informed version.
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 Last edited: by mediadogg
DVD Profiler Unlimited RegistrantStar ContributorGSyren
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Okay, I read up a little bit about Dolby Prologic, and I think I understand it a bit better now. Maybe. Correct me if I'm wrong.

So, if I understand correctly, basically the more similar the two channels are, the more it will send that to the center speaker and correspondingly lower the volume on the left and right speaker. So a mono signlal would play pretty much only in the center speaker. Fine so far.

But - again if I understand correctly - if you have a stereo track where a passage has more or less the same sound in both channels, then this would also be played mainly in the center speaker. Is that right?

So that would more or less sound just like the mono track? And if so, it wouldn't be a very reliable test for mono vs. stereo unless you made sure that you listened to a passage where there was a stronger stereo effect?
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DVD Profiler Desktop and Mobile Registrantmediadogg
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The "it" you are talking about is the amalgamation of the codec being used, and your receiver settings, including manual adjustments (e.g. "balance", or a "mono" switch, or down-mix settings and the list goes on).

Based on all the discussions, I'm coming to a very simple way of thinking about it. If there is one channel in the audio stream, the source is mono. If there are 2 channels, the source is stereo (seems to borne out by the code I am looking at - that Dual Mono code seems never to be hit). And so forth.

Now, what you HEAR in which speaker is totally dependent on setup , configuration, and actual channel content.
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 Last edited: by mediadogg
DVD Profiler Unlimited RegistrantStar ContributorGSyren
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Quoting mediadogg:
Quote:
The "it" you are talking about is the amalgamation of the codec being used, and your receiver settings, including manual adjustments (e.g. "balance", or a "mono" switch, or down-mix settings and the list goes on).

That may well be so, but the bottom line is - is listening to the center speaker vs the left/right ones a reliable way to determine if it's mono or stereo. And my understanding is that it is not, if you're looking for a quick determination.
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Quoting GSyren:
Quote:
Quoting mediadogg:
Quote:
The "it" you are talking about is the amalgamation of the codec being used, and your receiver settings, including manual adjustments (e.g. "balance", or a "mono" switch, or down-mix settings and the list goes on).

That may well be so, but the bottom line is - is listening to the center speaker vs the left/right ones a reliable way to determine if it's mono or stereo. And my understanding is that it is not, if you're looking for a quick determination.

Correct. Although there is a "DIRECT" setting that some A/V receivers have that i think turns off the codecs. That might be a way ...
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 Last edited: by mediadogg
DVD Profiler Desktop and Mobile RegistrantStar ContributorAiAustria
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Quoting GSyren:
Quote:
Okay, I read up a little bit about Dolby Prologic, and I think I understand it a bit better now. Maybe. Correct me if I'm wrong.

So, if I understand correctly, basically the more similar the two channels are, the more it will send that to the center speaker and correspondingly lower the volume on the left and right speaker. So a mono signlal would play pretty much only in the center speaker. Fine so far.

Correct.
Quote:
But - again if I understand correctly - if you have a stereo track where a passage has more or less the same sound in both channels, then this would also be played mainly in the center speaker. Is that right?

Yes.
Quote:
So that would more or less sound just like the mono track? And if so, it wouldn't be a very reliable test for mono vs. stereo unless you made sure that you listened to a passage where there was a stronger stereo effect?

More or less is the key word. If the two chanels are identical, they are "downmixed" to the center speaker. The other way around: if you can hear anything on the left or right channel, it is not a mono signal.

But be carefull to deactivate any special features of the receiver. The artificial enchancements, which many receivers offer, use all channels, regardless of the source.
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DVD Profiler Desktop and Mobile Registrantmediadogg
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Gunnar, I have to issue a retraction. DVDPca, as I think you know, is an augmented mashup of a bunch of other programs, such as DVDInfo, BDInfo, two different IFO scanners, two different movies players, and a bunch of other snippets. During the testing, which a bunch of people contributed to, I experimented with various mixes and matches, fixed some bugs and added some new features. I stopped when I was getting mostly reports that the metadata matched exactly other tools such as PowerDVD, and running times were computed exactly. Extra features included extracting other metadata from the IFO files and off the disk.

As a result, when I looked at the code the other day, I posted a snippet containing "DualMono". That code, as far as I can tell, will never be hit in the current version of DVDPca, whose code is a jumbled mess.

DVDPca, for DVDs will only designate "Mono", if there is only 1 channel. period.

I am currently looking at some updates, and I might experiment with at least putting in the logic that is capable of outputting "Dual Mono." Whether there is a DVD out there, with metadata that will trigger the code, is anybody's guess.

By the way, the IFOs you sent, when parsed, identifies an AC3 codec (Dolby) and 2 channels.

I was trying to find an analogy for what we are dealing with. This is as close as I could come:
Quote:

A car is registered as a 5 passenger car, if it can legally carry a maximum of 5 passengers. It retains that designation, no matter how many people are actually traveling.

However, in a "high occupancy" lane, you are required to have at least 2 passengers, otherwise get a ticket from police.


There is no policeman that prevents, while mastering the DVD, two identical mono sources from being passed to the Dolby AC3 encoder as a "stereo" signal. You get pseudo surround, unless you turn off the Dolby processing of the receiver. In this case, if the cover says "Mono", then depending on your point of view, both the cover and the metadata are correct.
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 Last edited: by mediadogg
DVD Profiler Unlimited RegistrantStar ContributorGSyren
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For what it's worth: All discs I looked at, whether 1 or 2 channels, were identified as AC3 by DVDPca. But that was only maybe half a dozen discs, so that could be just coincidence.

Barring a good way to display channel difference (l-r), it still seems to me that an educated guess is the best way to identify 2-channel mono. Not sure how well that would fare with voters/scanners though.
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Quoting GSyren:
Quote:
For what it's worth: All discs I looked at, whether 1 or 2 channels, were identified as AC3 by DVDPca. But that was only maybe half a dozen discs, so that could be just coincidence.

Barring a good way to display channel difference (l-r), it still seems to me that an educated guess is the best way to identify 2-channel mono. Not sure how well that would fare with voters/scanners though.

I would only be concerned if DVDPca produced different metadata than other trusted tools. If you find such a case, then let me know, and send me the IFOs.

Also, you have actual 1 channel discs? Wouldn't mind taking a look at those IFOs as well. Thanks.

In terms of displaying (L-R), a simple hardware circuit will do it. I have an old Radio Shack voice remover that was used for Karaoke, if you want to play with it. Pay for shipping and you can borrow it.

Or, I could build you a little custom circuit that works with headphones. let me know.

But again, if during mastering, the mono signals are passed thru a Dolby encoder, there is pseudo surround info added to the 2 channels. Check the Wiki for Dolby for a full discussion. So then you go from M->L and M->R, to stereo AC3 Lt and Rt, where Lt and Rt are the augmented pseudo surround channels. In that case, I think the subtraction trick still works, but I am not 100% sure.
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 Last edited: by mediadogg
DVD Profiler Desktop and Mobile RegistrantStar ContributorAiAustria
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http://www.mediafire.com/file/dfgn2trtssxc5jv/VTS_01_0.IFO/file
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DVD Profiler Unlimited RegistrantStar ContributorGSyren
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I was going to say that I do have several 1 channel discs, bur the problem would be to find them.
But now that AiAustria has provided an example maybe I don't have to?
If you need further examples, mediadogg, I can certainly take a look.
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DVD Profiler Desktop and Mobile Registrantmediadogg
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Quoting GSyren:
Quote:
I was going to say that I do have several 1 channel discs, bur the problem would be to find them.
But now that AiAustria has provided an example maybe I don't have to?
If you need further examples, mediadogg, I can certainly take a look.

Thanks, let me start with that one. But if DVDPca already reports mono, I don't need to ...

Note to AiAustria, Thanks, but I need all the IFOs. Is that the only one?

I'll take a look anyway, but it would be interesting also to know: what does a DVD player say?

I just looked at the profile. Both tracks are "Dolby Digital - Mono".

I will be very eager to see the actual bits in the metadata! 
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 Last edited: by mediadogg
DVD Profiler Desktop and Mobile Registrantmediadogg
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Quoting GSyren:
Quote:
For what it's worth: All discs I looked at, whether 1 or 2 channels, were identified as AC3 by DVDPca. But that was only maybe half a dozen discs, so that could be just coincidence.

Barring a good way to display channel difference (l-r), it still seems to me that an educated guess is the best way to identify 2-channel mono. Not sure how well that would fare with voters/scanners though.


Quote:
I was going to say that I do have several 1 channel discs, bur the problem would be to find them.
But now that AiAustria has provided an example maybe I don't have to?
If you need further examples, mediadogg, I can certainly take a look.

Not sure how to interpret this. If you used some 1 channel discs, then you obviously could find them.  What did I miss?
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 Last edited: by mediadogg
DVD Profiler Unlimited RegistrantStar ContributorGSyren
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Quoting mediadogg:
Quote:
Not sure how to interpret this. If you used some 1 channel discs, then you obviously could find them.  What did I miss?

Simple. I pulled some titles at random, and I made no note of which they were. At the time I wasn't actively looking for single channel mono, but at least one of them happened to have just that. I'm sure I could find some again, but I might have to go through quite a few to find one. And I will if you need it.
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DVD Profiler Desktop and Mobile Registrantmediadogg
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Never mind everybody regarding examples. The nose on my face got in the way of the obvious.

A simple filter search on my own collection, identified a whole bunch of DVDs and BDs with MONO audio tracks. I will just run a few through DVDPca and compare what it finds to the existing DVDP profiles. If I find a difference, I wil examine the code and the actual IFO bits.
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 Last edited: by mediadogg
DVD Profiler Desktop and Mobile Registrantmediadogg
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Ok, I am finding mostly good correspondence, but I just hit one that will make it relatively easy for me to sort out bugs. The IFO scan shows all tracks and languages, dead equal and the same as the profile in DVDP. But my GUI drop downs are blank. Clearly a bug there. But it shows that the hard part is correct - the IFO parsing. The mono channels, in this case, were Commentary. Little Miss Sunshine, 024543403319, US.
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