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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 Unlimited RegistrantStar ContributorGSyren
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The rules say:
Quote:
Select Mono for both 1-channel and 2-channel mono.

Well, that is sometimes easier said than done. Even listening with headphones, it can be difficult to be sure that a 2-channel track is actually mono. And cover info is notoriously unreliable.

Checking IMDb can be a help. If they say that the original sound was mono, and there is no mention on the DVD/BD that it has been remixed, then the likelyhood that it is actually mono is very high. But IMDb is not always reliable, and looking up everý title is a bit time consuming.

What would be helpful, though, would be to be able to display the waveforms for both tracks and compare them. If they are constantly the same, then it is mono.

Does anyone know of any software (preferably freeware) that can monitor the audio waveforms while the DVD/BD is playing? Ripping isn't practical; takes too long. Thorough profile auditing is time consuming enough. 
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Gunnar
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This would depend on your receiver and settings, but normally mono audio should play through the center speaker only. If the left and right channels are different you will also hear them through the left and right front speakers.
Patrik
 Last edited: by iPatsa
DVD Profiler Unlimited RegistrantStar ContributorGSyren
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The problem isn't differentiating between 1-channel and 2-channel.
The problem is differentiating between 2-channel mono and 2-channel stereo.
2-channel mono will play through the left and right speakers, just like 2-channel stereo.
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Gunnar
 Last edited: by GSyren
DVD Profiler Desktop and Mobile Registrantmediadogg
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Well it is a little bit what everybody said.

There is not necessarily a 1-1 correspondence between:

(1) What is actually on the DVD audio tracks
(2) What is said to be on the tracks (cover info, track info encoded on the DVD)
(3) What signal is actually sent to each speaker (see iPasta comments)
(4) What you can see by viewing the signals in the time domain

In fact:

(1) Only the recording engineer knows
(2) Can be wrong on the cover, or even on the DVD. Software such as DVDInfo (which DVDca is derived from), actually reads the encoding from the track info on the DVD. This information would likely have been supplied by the recording engineer.
(3) Depends on your home theater wiring and receiver settings.
(4) It would be virtually impossible to visually compare two audio waveforms in real time (I mean with your eyes - yes, software and/or hardware that can sample the signal can do it.)

An example of (3): You could incorrectly determine that a signal was "mono" if an error in your wiring sent both left and right channels the same signal (say the left channel), or if there is a "mono" setting on the receiver, artificially mixes a stereo signal down to mono by adding the two channels, and sending the sum to both speakers.

If you want a simple way to tell whether left and right signals coming from a stereo output are exactly the same, you can subtract them. If you have simple electronics skills, this is easy to do. Probably a ton of circuits on Google. If Left and Right are EXACTLY the same in amplitude at every instant in time, you will hear dead silence when the signals are subtracted ( a waveform will show a flat line). Theoretically it would be possible to do this in software while the DVD was playing, as Gunnar suggests.

Legacy receivers used to have a switch for this, and this method was sometimes used to synthesize pseudo surround effects; e.g,,  Left surround got (L-R), right surround got (R-L), and center got (L+R) in cheap equipment.

Ah, I almost forgot: the real issue is: what do the rules require that you submit? I think it is (2) - what is encoded on the DVD.
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 Last edited: by mediadogg
DVD Profiler Unlimited RegistrantStar ContributorGSyren
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Quoting mediadogg:
Quote:
Ah, I almost forgot: the real issue is: what do the rules require that you submit? I think it is (2) - what is encoded on the DVD.

Surely, the encoding doesn't differentiate between 2-channel mono and 2-channel stereo? It's the content that differs, not the encoding.

(1) What is actually on the DVD audio tracks must be the right answer, as I see it. And yes, perhaps one would need software to compare the tracks to really determine what is what.
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Gunnar
 Last edited: by GSyren
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Quoting GSyren:
Quote:
2-channel mono will play through the left and right speakers, just like 2-channel stereo.

... what iPatsa meant: If you switch to Dolby, Dolby Surround or Dolby Prologic decoding, then a mono track is centered, while a Stereo track is mixed betwenn the three channels.
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DVD Profiler Desktop and Mobile Registrantmediadogg
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Quoting GSyren:
Quote:
Surely, the encoding doesn't differentiate between 2-channel mono and 2-channel stereo? It's the content that differs, not the encoding. ....

I think in fact it does. I will double check.

And as far as contributing, I can't imagine that Ken envisioned the community actually monitoring wave forms to make a contribution. Take the word of the recording engineer and call it a day. Geez, we can't even agree on the spelling of a name, or how to handle Asian names.       
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 Last edited: by mediadogg
DVD Profiler Desktop and Mobile Registrantmediadogg
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Yes, I found code in DVDPca/DVDInfo that handles the "AudioMode" descriptor on the DVD, which can have a value of "Dual Mono" for a channel count of 2. My understanding of Dual Mono, is that the same signal is designated for the both left and right channels.

                if (ChannelCount == 2)
                {
                    switch (AudioMode)
                    {
                        case TSAudioMode.DualMono:
                            description += " / Dual Mono";
                            break;

                        case TSAudioMode.Surround:
                            description += " / Dolby Surround";
                            break;
                    }
                }

Then there is "ChannelLayout" descriptor. Here is the code for that:
                  switch (ChannelLayout)
                    {
                        case TSChannelLayout.CHANNELLAYOUT_MONO:  // Send to center channel speaker.
                            description += "1.0";
                            break;
                        case TSChannelLayout.CHANNELLAYOUT_STEREO:
                            description += "2.0";
                            break;
                        case TSChannelLayout.CHANNELLAYOUT_MULTI:
                            description += "5.1";
                            break;
                    }

Now, you ask: is there such a thing as channel layout of "mono" for channel count = 2? Here is that code:

                if (ChannelLayout == TSChannelLayout.CHANNELLAYOUT_MONO &&
                    ChannelCount == 2)
                {
                }

Seems like even the original coders of DVDInfo punted on that one! 

I would encourage you to try DVDPca if you want to see what is encoded on the DVD. Back when I was testing, I think it was found to be very accurate.

By the way, just to be clear, the "encoding" I am talking about is the encoding of descriptive information (metadata) in the IFO files on the DVD, not the audio stream encoding.
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 Last edited: by mediadogg
DVD Profiler Unlimited RegistrantStar ContributorGSyren
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Quoting mediadogg:
Quote:
as far as contributing, I can't imagine that Ken envisioned the community actually monitoring wave forms to make a contribution.

You're right. This whole thing actually started by me wondering how Ken envisoned that we would tell 1-channel mono from 2-channel mono.
Quote:
By the way, just to be clear, the "encoding" I am talking about is the encoding of descriptive information (metadata) in the IFO files on the DVD, not the audio stream encoding.

Ah, thanks! Now the penny dropped!

So that kind of shifts the focus a bit. Why is the overwhelming majority of old mono titles mastered as 2-channel mono? I can only assume that it is because the media company figured that most customers would prefer to have a wider sound image, coming from both main speakers rather than from the center speaker (if any). But if that was their intention, would the mastering engineer really care enough to create different metadata for mono and for stereo, if the audio was supposed to be presented the same way anyway, i.e. through the left and right speakers? Sounds like it would be just as unreliable as the back cover info.

So that seems to put as back at square one, doesn't it? We just have to make an educated guess. If the back cover says "mono", then it probably is. But that's about as far as I would trust the cover info. If it's an older movie and it days "stereo", I would be a bit suspicious and I would dig a bit. If it just says something like "Dolby 2-channel", or if there is no mention of the sound encoding, then I suppose I would go with an educated guess.

A relatively safe guess would be that fullscreen b&w movies from before 1960 would be mono unless there is info that says it was re-mixed. Color or widescreen would indicate a bigger budget which might mean more expensive audio, i.e. stereo (or better). Why 1960? No special reason, I just picked a year. It just seemed like stereo would become more popular after that.

Checking with IMDb is of course an option. If it says mono, and there is no indication of a remix, then I would assume that it is probably mono. That said, I know that Disney has remixed many of it's old cartoon features for DVD release.

So that brings me full circle back to "How did Ken envision that we would tell 1-channel and 2-channel mono apart?"
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Gunnar
DVD Profiler Desktop and Mobile Registrantmediadogg
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My point that you forgot: how about check what is on the actual DVD (not the cover)? There is a placeholder in the specifications for somebody to tell you "Dual Mono". But there is no requirement for them to do so. If they used it, DVDPca and DVDInfo will display it. In those cases, no need to guess. Hmm, well I don't know if it is still working. Been a long time since the last update. Sorry about that. Guess I should do an overhaul and see what happens.
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 Last edited: by mediadogg
DVD Profiler Unlimited RegistrantStar ContributorGSyren
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Quoting mediadogg:
Quote:
how about check what is on the actual DVD

Eh? You've got me confused now. I thought I covered metadata ("would the mastering engineer really care enough to create different metadata for mono and for stereo?"). Or are you talking about something else?
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Gunnar
DVD Profiler Unlimited RegistrantStar ContributorGSyren
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By the way, I just found out that VLC player actually can display waveforms. And I agree that it is impossible to say that ttwo waveforms are identical and therefore determine that it must be mono. But it is possible in many cases that waveforms are sufficiently different that you can tell with a fair degree of certainty that it is stereo.

Not sure how useful it is, though, since you would have to look for places where the tracks really are quite different.
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Gunnar
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Quoting GSyren:
Quote:
..., would the mastering engineer really care enough to create different metadata for mono and for stereo, if the audio was supposed to be presented the same way anyway, i.e. through the left and right speakers? Sounds like it would be just as unreliable as the back cover info.

That is exactly my observation. The only way to differentiate, I found, is the Dolby Surround Decoding.
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DVD Profiler Unlimited RegistrantStar ContributoriPatsa
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Quoting GSyren:
Quote:
The problem isn't differentiating between 1-channel and 2-channel.
The problem is differentiating between 2-channel mono and 2-channel stereo.
2-channel mono will play through the left and right speakers, just like 2-channel stereo.


Switch to Dolby Prologic Decoding. It will most certainly play 2-channel mono through the center speaker and 2-channel stereo through the left and right speakers.
Patrik
DVD Profiler Unlimited RegistrantStar ContributorGSyren
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Quoting iPatsa:
Quote:
Switch to Dolby Prologic Decoding. It will most certainly play 2-channel mono through the center speaker and 2-channel stereo through the left and right speakers.

I don't have a center speaker on my PC, nor any Dolby Prologic Decoding (as far as I know, anyway). And the rules surely can't assume that all users have a setup with a center speaker. And wouldn't Dolby Prologic Decoding depend on the metadata to know if it is mono or stereo? So if the metadata is unreliable, then the Dolby Prologic Decoding is unreliable as well, right?

Personally I do have a 5.1 setup in my living room, but that's not where I do my profiling.
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Gunnar
 Last edited: by GSyren
DVD Profiler Unlimited RegistrantStar ContributorT!M
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Quoting GSyren:
Quote:
"How did Ken envision that we would tell 1-channel and 2-channel mono apart?"

I daresay he didn't envision that at all. I think he really didn't expect anything beyond entering what the cover says. It's just unfortunate that cover information is so often completely inaccurate.
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