Making a DCP from a 2-channel stereo Blu-Ray

[Mike Blakesley]

We have a private show coming up of a classic movie from 1990, and the source Blu-Ray has a L-R stereo soundtrack. For theatrical use, when making the DCP, should I:

- Leave it as L-R

- Add the center channel along with L & R to blend it together

- Pipe all the sound to the center only?

Recommendations would be dandy. Thanks!

[Chris Haller]

I would leave it as L-R. Most home theaters mimic the setup of a standard theatrical space, so it should sound fine through the LR of your theater. I've run a handful of blu-ray to DCP features with LR and it sounds correct in that configuration.

[Marcel Birgelen]

Unless you really know what you're doing and do have the tools to do a proper upmixing, I'd leave it alone. The L + R will create a "virtual ghost center", which will not be as strong as a real center channel, but what works on TV, also works in the cinema.

One thing worth checking: You have a Trinnov Ovation 2 as sound processor, don't you? That thing should support some kind of 2-channel upmixing, at least with the right licenses. Might be worth taking a look at and maybe someone with some actual experience with those things may chime in.

[Brandon Wood]

Agree with others saying leave it as L-R and it should sound fine. I do have to say that I have used DCP-o-Matic's feature where it creates a center channel with a high success rate. Of course, the purists will tell you that's blasphemy or something, but in my experience, it does pretty well, and it's no different than a home theater system creating a center-channel on the fly.

[Steve Guttag]

Okay...I'll be "that guy." You all are nuts leaving a cinema show as L/R (avoid using L-R as it reads as L minus R, which is something different). No mixing suite thinks that Left and Right speakers are 20-60-feet apart when they mix a 2-channel. It sounds horrible. Dialog is hollow as the center is phantomed. Even back in the mid 20th Century we knew not to do that!

If your processor has a pro-logic option, that is what I would use. Sadly, the Dolby CP950 dropped the ball on that one. While they do have upmixing for 2-channel from NON-DCP sources...they opted to not offer that for DCP sources. I provide a "DCP 2.0" on our Q-SYS systems to handle this.

DCP O Matic does have an upmix option with mixed results.

I would not create a center with a mere mix of L/R as that will just smear the sound stage into a very wide sounding mono. The audio should have steering.

[Chris Haller]

Okay...I'll be "that guy." You all are nuts leaving a cinema show as L/R.

In my defense, I'd never take a blu-ray and turn it into a DCP for an audience. But for like a one off private screening? I am a little less precious.

[James Gardiner]

If your processor has a pro-logic option, that is what I would use. Sadly, the Dolby CP950 dropped the ball on that one. While they do have upmixing for 2-channel from NON-DCP sources...they opted to not offer that for DCP sources. I provide a "DCP 2.0" on our Q-SYS systems to handle this.

Sorry, no, I would not do this. Dolby Laboratories Pro Logic is a matrix decoder system. Ask ChatGPT for the technical details, but in essence the results can be unreliable and inconsistent.

I would expect more modern tools, even DCP-o-matic, to do a better job of rendering a centre channel. However, it is still a compromise and detached from the producer’s original intent.

Personally, I tend to leave content in stereo. For ads, it matters less. But for feature content, I prefer to leave it as supplied.

Stereo playback in a cinema generally does not sound ideal, as cinema auditoriums are designed around at least 5.1 playback, with the dedicated centre channel being one of the most noticeable differences. Even so, leaving the mix in stereo will usually sound closer to the producer’s intended presentation than attempting an artificial matrix-derived centre extraction.

[Steve Guttag]

Having done quite a bit around this, you are just flat out wrong. Go ahead, do some tests of your own, in a "typical" cinema. Put a pro-logic circuit in and out. Find me the mix that anyone really would prefer the straight up stereo. Furthermore, when taking a mono movie...they will have it such that it is the same track on both channels...would you really rather hear that as 2-channel mono? With a pro-logic decoder, you'll get a hard center channel. Yes, you could just use one channel and remap that to center but that is less handy in most systems.

See how many of those Blu-ray stereo mixes are really Lo/Ro and not Lt/Rt. Whomever made the Blu-ray did not have speakers as far apart as a cinema has in mind. You are not creating anywhere near that mix in a cinema and you are compromising the dialog while doing it.

[James Gardiner]

@Steve, maybe it’s because I managed a post-house for a long time and still work part-time in an audio dubbing facility. Accountability is everything. Introducing a filter when you have no real idea what the result will be is unwise, especially when it can expose you to contractual compliance issues. However, since this is a "best-effort" workflow, it’s probably not a problem, and "It sounds better this way" usually justifies the perceived superior result.

[Marcel Birgelen]

I'm largely with James with this one. The problem is, when you're unexperienced with this, you easily are going to make the situation worse by applying some random filters. I've done quite a few upmixes from stereo over the years, so I consider myself halfway qualified. While I agree with the essence of what Steve mentions, I think you also need to put it into perspective. It's a private showing with limited source material, and how bad the stereo image will be, also depends on the size and layout of the room and where people are sitting. In smaller rooms with people sitting more towards the back, the issue is pretty limited.

Where I slightly disagree with James, is the ProLogic matrix decoding angle, because those things are made exactly for this purpose and work pretty well out-of-the-box. While certainly not 100% reliable, I think that the general result with "Pro Logic" matrix decoding will sound better than the "flat stereo" mix, especially with sound mixes that were mixed with matrix decoding in mind. Usually, people are pretty preoccupied with the movie itself and not constantly busy with analyzing if this or that sound came exactly from the right direction, so you usually have some leeway there. With the brunt of the dialog going through the center channel and even a bit of residue through the surrounds, it will sound a whole lot more "cinematic" than just the flat L/R mix. But the results are also highly dependent on the mix itself (was the stereo mix itself matrix encoded?), so testing what sounds best is the answer here IMHO.

Regarding automatic upmixing: I've had quite some good results with DTS Neo:6 and even Dolby ProLogic II. Both are flawed formats, but those "formats" also work pretty well for mixes that were not matrix encoded. So, if your audio processor supports one or two of them, it's always worth trying them out, maybe even together with the customer, if you have the time to do so. For example, the AP20/25 supports DTS Neo:6 and the CP750 will do ProLogic II.

Being a movie from the 1990s, it was probably mixed with some matrix encoding in mind for the theatrical release (if it had one), so the original intent was, most likely, at least a 4-channel mix like Dolby Stereo. If not, you'd rather expect the source material to be just mono than stereo.

[Marco Giustini]

Uhm... I see James and Marcel's point but I think I am on Steve's side here. Yes, I don't like applying a filter where it's not supposed to be applied. How many cinemas have their CP750/CP650 set to EX all the time even with DC? I've seen entire multiplexes like that.

However, applying ProLogic seems to be the lesser of two evils here. Stereo in cinema is just bad. Plain bad. It WILL sound awful. ProLogic will normally sound ok on a Stereo track - it might spoil some segments which are supposed to sound in a specific way but the audience will be thanking you IMHO.

Of course if I were in a Post Production environment, then adding ProLogic to a Stereo track is just a big no-no.

One thought though I share with Marcel: a movie from the '90s in STEREO? Are we assuming this is NOT Pro-Logic encoded? Who would make a Stereo-only movie in the '90s?

[Ryan Gallagher]

We do a fair bit of BR screenings here. I’ve only recently started sometimes converting them to DCP for cuing/playback reliability,

it all depends on what features your processor is going to offer, versus doing it in dcpomatic etc.

Some features will only maybe be available to you if you run the hdmi source from the disc. If DCP conversion is the only/best option, I’ll tend to make both versions and decide which I like via listening, not fully trusting the upmixing tools in DOM I like to have the 2.0 version to fall back on.

[Jim Cassedy]

We had a local tech-business rent an auditorium for a private screening last month.
Our programming/booking department informed me that there was no DCP available
of the 1996 title they wanted to watch, and sent me a blue ray, which had a strictly
2ch stereo sound mix. Since the program that day involved several other pieces of
content, some of which were already DCP, I decided to convert the Blue-Ray, so
that I could automate the event, since, as usual, it was one several I needed to deal
with that day, to the less I needed to 'babysit' that show, the better.
It was a small (apx 35seat) auditorium- I did it as a straight 2ch stereo audio mix
and it was just fine. In full disclosure, it was a documentary style movie, and not
some mega-action flick, so plain-old 2ch stereo was just fine.

[Ed Gordon]

We have a private show coming up of a classic movie from 1990, and the source Blu-Ray has a L-R stereo soundtrack. For theatrical use, when making the DCP, should I:

- Leave it as L-R

- Add the center channel along with L & R to blend it together

- Pipe all the sound to the center only?

Recommendations would be dandy. Thanks!

Another option is to replace the soundtrack. I had a Bluray of an old 60's roadshow movie that only had the english audio in stereo. I found the old DVD release of the movie that included the multichannel mix. I extracted the multichannel soundtrack and added it to the MKV I created from the bluray.

This may be more of a hassle if you are under a time constraint, so using the stereo audio as is may be your best option.

What is the name of the movie are you screening privately?

[Gordon McLeod]

We make our DCPs with Davinci resolve studio version and the DTS nerual plug in that offer a prologic upmix to the DCP