stereo to 5.1 using mid-side decoder

[Miriana]

I have a short film which I am making into DCP but it has stereo only audio. It looks to me like the stereo is really 2 mono tracks. This was a conversion from tape.

It is a drama with mainly dialog, some SFX and some music under the dialog.
I understand that it's better to have the dialog coming from center speaker so I used the mid-side decoder using 5.1 preset in DOM
I did get 6 channels. Only the center channel had audio, but no audio at all in Right and Left channels.
I did expect channels LFE and Ls and Rs to be empty.

Is this the way is is supposed to be? Will it create a problem when played on a cinema?

What is the correct way to achieve this?

Thank you
Miriana

[phili2p]

Hi Miranda,

From your description, it seems quite allright to me to have this kind of result.

First of all, the source is 2 channel audio from tape - but not necessarily stereo but two times mono. Have a look at the waveform monitor or the peak level (of the daw software of your choice or in the timeline of your nle): if channel 1 and 2 are always the same, you have a monofile.

Speaking at a very low level of technical details: The mid-side-upmix works on the difference between channel 1 and 2. Everything that is the same on both channels, is mono, mostly expected to be dialogs and voice and by that perfectly placed on the center. The rest of the audio remains on channel 1 or 2.
The mid-side-upmix will never affect any other channel. The other upmixers might do it but they are not recommened and as I suggest your source file to be mono, they won't work anyways.

From a festival's perspective: Trust the Center Speaker!
Rather keep it mono, stereo or LCR than making some surround experiments as long as you don't have someone who really knows when to use it. The same with LFE which is only rarely used and works different to subwoofers you might know from your home theater system.

Last but not least: Take your DCP to your local cinema for a quality check. You might find out that you won't miss anything. Maybe you can make a non-upmixed version, too?

Best wishes
Philipp

[Miriana]

Hi Philipp
I guess my question is if it is OK to have sound only on the CENTER speaker and nothing coming from the left and right speakers. Or should I put these mono files on the left and right speakers as well as having it in the CENTER speaker.

And I chose 5.1 as the preset but should I use another - I wasn't sure how to select 3.1
Thanks for your reply
Miriana

[phili2p]

Hi Miranda,

Having audio on the center only means it's a mono file. And by that, it's usually fine.

I thought you used the mid-side decoder not the stereo to 5.1 upmixer? Nevertheless, as far as I know both surround upmixers needs a careful check at the end. Never trust those automatisms too much.

Here's what they do: https://dcpomatic.com/manual/html/ch07.html

Anyways, if you are able to bring both versions (or at least) into a cinema and maybe it's a very wide area, you should run a test in a real life evironment.

Best wishes
Philipp

[Miriana]

Thank you Philipp
Yes I used the mid-side decoder for the up mixing with 5.1 mapping.
I was concerned that there was sound only in the CENTER channel and nothing in left or right channels.
So if I understand you correctly, this should not be a problem.

Yes I had a look at the waveforms in the original video file in my NLE and they do appear that left and right are the same, therefore dual mono.

Do you think it's better to leave this video as stereo instead - would the sound still come out of the CENTER speaker?

I know it's always best the check in a cinema but this little film will be played in another city.

Again thank you for your help
Miriana

[phili2p]

Hi Miranda,

having the audio on the center speaker only is fine: the audio will come directly from the screen (as in most cinemas the center box is placed behind the screen).
Having the audio on the left and right speakers only might be even more problematic if the first row is close to a wide screen as an audio gap might appear in the middle.

I would still recommened to run a test at your local cinema to check if everything went fine with the DCP. From the server ingest to loudness experience in cinema. Please note that cinemas have a quite good international standard and if the DCP looks and sounds odd to you in your local cinema, it won't be better in any other venue worldwide. As long as it's next to you you can improve some aspects. If it's shipped to anywhere, you'll need to send a new version by courier to start your film in time. A hellish trip for audience, projectionists and you.

Enjoy the screenings!
Phillipp

[Miriana]

Thank you Phillipp for your advice.
I will certainly try to test at a cinema and check everything.
All looks and sounds OK on my computer but there is nothing like a real world test.
I appreciate you helping me understand more about DCPs
Miriana

[Carsten]

Agree to everything Phillip wrote. Having mono/center channel only is completely okay if the e.g. the source content is mono or dual-mono.
No problem to have 5.1 channels in a DCP, with only the center channel containing actual audio. Many professional studios do this wrong, placing mono audio on both L and R.

- Carsten

[Miriana]

Hi Carsten
Thank you for confirming this for me
Miriana

[Guddu]

Hi Carsten
Thank you for confirming this for me
Miriana

Dear Miriana,

Could you please confirm your experience with this one? I see that you used mid-side decoder. How was the user experience in the cinema?

Regards,
Anurag