Making a DCP from a Blu-Ray with only L-R sound

[Mike Blakesley]

If I'm makind a DCP out of a Blu-Ray that only has a L-R soundtrack, when running it thru DCP-O-Matic, how should I handle the sound?

• Leave it as is, just L & R
• Make it L - C - R
• And should I add the surround channels?

If it's a concert video, I can see the case for surround being desirable. But would that make it sound weird?

How about a movie with mono sound? Is it best to just run it through the center channel, or does it make sense to do L-C-R to give it a more full sound?

[Thomas Piccione]

This advice is from a rather small "screening room," if you can even call it that, (it's a lecture hall most of the time) which only holds 200 people, so your mileage may very.

From a little bit of experimenting, I've found that leaving it "as is" has generally worked the best for me. If it's LR, send it to just the left and right. Adding the center can work, but I've had it do interesting things when downmixing a couple times, and our room is so small the difference is not really noticeable. Similarly, mono movies just go through the center channel.

Adding the surround channels is generally something I would more strongly recommend against, as sending the same signal there as in front has never yielded good results when I've tried. If you think about how surround channels are typically mastered, they are at a significantly lower level, and generally just have a lot less going on than everything behind the screen. Depending on the size/shape of your auditorium there might also be noticeable delay or phase alignment issues. These things don't matter with content intended for it, but you may run into some snags when you play exactly the same audio through speakers pointing at each other.

DCP-O-Matic does have 2 options for up-mixing to 5.1, up-mixer A and B, but I've had very mixed results with them. Sometimes it's pretty alright, and sometimes it's completely unusable.

[Leo Enticknap]

If it's a mono movie, you absolutely want it to play on the center channel only. This is easy to achieve in DCP-o-Matic - just route both left and right in the source to center on the DCP, and use the "attenuate by -6dB" option on both. Mono played simultaneously through left and right will create an annoying echo effect for anyone who is not sitting close to the centerline (screen to back wall) of the auditorium.

IMHO, for upmixing from 2.0 to 5.1 or 7.1, hardware ProLogic (or knockoff) decoders do a far better job than DCP-o-Matic (no offense to Carl - it's still a very useful thing to have if you can't play through a hardware decoder). Q-Sys and the DMA8+ are both examples. Annoyingly, the CP750/850/950 will not let you put two channels of AES through the ProLogic upmixer: only analog nonsync.

[Steve Guttag]

It has been my experience that 2-channel (Left/Right only) don't sound good in cinemas. The speakers are spread too far apart to give a proper sound stage and if there is any speaking, the phantom channel between them doesn't work well and is very dependent on where one is sitting. I try to provide a DCP 2.0 format in my systems. I'm reasonably certain that the CP750 can do a pro-logic decode of DCPs.

Screen Shot 2023-01-17 at 7.31.02 AM.png

The CP950 has definitely omitted that option from the PCM input (it's there on the coax inputs). I forget if the IMS3000 has it as an option since the only places I have audio processors in the server are for Atmos and, thus far, all of my Atmos systems have Q-SYS, where I put a prologic decoder for DCP 2.0 content.

[Jim Cassedy]

A good number of the 35mm films I run are mono. I've made attempts at rerouting or re-patching the
mono sound to come out of the L & R or L-C-R screen speakers, in an attempt to give it more of a
"full sound", as Mike suggests, but it almost always wound up sounding not so good, or else it would
sometimes it sound pretty good in some parts of the auditorium, and pretty bad in other parts. I asked
a couple of sound experts at Dolby that I was working with at the time for advice, & their advice was
to "leave it center screen mono". - - and even though I did continue experimenting with mulit-speaker
mono a few more times, I always found that just 'leaving it center channel mono" was sound advice.

[Carsten Kurz]

DCP-o-matic offers an LCR, and two experimental 5.1 upmixers. LCR works nicely for typical audio tracks (e.g. dialog over a stereo background track), and as Thomas says, both upmixers deliver 'upmixed' results, so, don't use them if you're not able to test the result in a cinema. It is, of course, quite easy (and fast) to create a straight stereo track OV, and one or two LCR/5.1upmix VFs using DCP-o-matic, so you can compare them.

Our AP20 processor offers a dts Neo:6 upmixer, and I use it for music/non-sync playback all the time. Unfortunately, both DCP-o-matic 5.1 upmixers are far from Neo:6 performance wise.
As far as I know, there is no high-quality open source 5.1 or 7.1 upmixer that DCP-o-matic could offer in addition to the existing basic ones.

And yes, a mono track should only go to the center speaker.

[Leo Enticknap]

I'm reasonably certain that the CP750 can do a pro-logic decode of DCPs.

The problem is that it's difficult to use in a show situation. Because the CP750 won't let you create multiple macros/presets - there is only one for the 8-channel AES input - if you're playing a mono or 2.0 CPL that you want to put through the ProLogic decoder that is in the same SPL as regular 5.1 or 7.1 content, you would either need to pause the show, connect to the CP750 using its app, change the processing method, then restart; or insert automation cues into the SPL that send the CP750 an API command to change the decoding method during the show. The latter is more feasible, but in arthouses and screening rooms that use little if any automation (i.e. the sort of place that would likely be playing a 1.0 or 2.0 DCP and want to use this feature), the chances are high that the projectionist won't know how to do it, and the tech won't be able to leave them with a "one push" solution for doing so (unless the room has an integration front end, e.g. Crestron or AMX).

[Gordon McLeod]

Is there a low cost prologic style up mixer that would convert a L/R to 5.1 before encoding with DCP Matic? Also is there any software synthesiser that do the old Kintek thing

[Vern Dias]

There is an open source utility called SOX that will do what you want. I have used it to encode Dolby Stereo to 5.1.


This is a script I used to encode a 2 channel stereo LaserDisc to 5.1 a while back.


Rem https://sourceforge.net/projects/sox/files/sox/14.4.2/

:: FRONT LEFT
:: ---------------
D:\Apps\sox-14.4.2\sox --no-dither "S1-S2.wav" -b 24 -r 48000 -c 1 "S1-S2-FL.flac" remix 1

:: FRONT RIGHT
:: -----------------
D:\Apps\sox-14.4.2\sox --no-dither "S1-S2.wav" -b 24 -r 48000 -c 1 "S1-S2-FR.flac" remix 2

:: Step 3 : GENERATE CENTER CHANNEL
:: ---------------------------------
D:\Apps\sox-14.4.2\sox --no-dither -v0.7071 "S1-S2.wav" -b 24 -r 48000 -c 1 "S1-S2-C.flac" remix 1v0.7071,2v0.7071 bandpass 50 20000

:: Step 4: GENERATE LFE CHANNEL
:: ----------------------------
D:\Apps\sox-14.4.2\sox --no-dither "S1-S2.wav" -b 24 -r 48000 -c 1 "S1-S2-LFE.flac" remix 1v0.5000,2v0.5000 lowpass 120

:: Step 5 : GENERATE SIDE SURROUND LEFT
:: ------------------------------------
D:\Apps\sox-14.4.2\sox --no-dither "S1-S2.wav" -b 24 -r 48000 -c 1 "S1-S2-SL.flac" remix 1v-0.8718,2v0.4898 delay 0.05

:: Step 6: GENERATE SIDE SURROUND RIGHT
:: ------------------------------------
D:\Apps\sox-14.4.2\sox --no-dither "S1-S2.wav" -b 24 -r 48000 -c 1 "S1-S2-SR.flac" remix 1v0.4898,2v-0.8718 delay 0.05

[Steve Guttag]

The problem is that it's difficult to use in a show situation. Because the CP750 won't let you create multiple macros/presets - there is only one for the 8-channel AES input - if you're playing a mono or 2.0 CPL that you want to put through the ProLogic decoder that is in the same SPL as regular 5.1 or 7.1 content, you would either need to pause the show, connect to the CP750 using its app, change the processing method, then restart; or insert automation cues into the SPL that send the CP750 an API command to change the decoding method during the show. The latter is more feasible, but in arthouses and screening rooms that use little if any automation (i.e. the sort of place that would likely be playing a 1.0 or 2.0 DCP and want to use this feature), the chances are high that the projectionist won't know how to do it, and the tech won't be able to leave them with a "one push" solution for doing so (unless the room has an integration front end, e.g. Crestron or AMX).

Leo,

I just haven't found that to be an issue at all. We have DCP2.0 cues at just about all of our locations, particularly art houses. One of the things I like about the CP750 API and architecture is that the decode mode is independent of input so the common Digital 1 cue works for everything. Then, it is a matter of having the right decode cue for the particular content.

Naturally, if you have a Dolby DSS server, all of the cues are there waiting for you:




If you are working with another server, the commands are simple enough (for prologic, 5.1 and 7.1):

• cp750.sys.pcm_2_channel_decode_mode_1 prologic
• cp750.sys.pcm_2_channel_decode_mode_1 lr_discrete
• cp750.sys.pcm_2_channel_decode_mode_1 4_discrete_sur

Naturally, I do recommend the eCNA automation but GDC and Doremi servers, of any vintage can handle these commands (as can the ICMP).

[John Thomas]

Everything everyone has already said is true and valid.

I would add that for a concert movie specifically, there may be a lot of value in using upmixing just to get the subwoofer involved. Makes it feel more like a real concert with real reinforcement, depending on the content of course. Personally I think using surrounds for concert footage is distracting unless it was specifically recorded and mixed for 5.1 to get the room reverb and crowd noise into the surrounds to achieve a sense of immersive space.

As has been already said, if you can get your processor to do ProLogic+SW on the the 2.0 mix, that's your best bet to try first. If not, make multiple versions and do some experimentation.


There is also the principled school of thought about not processing the source material in any way, which is also valid.

[Jim Cassedy]

Not entirely off-topic, but after writing my original post about my attempts to spread 35mm
mono film sound, I later recalled that Dolby's CP-45 had two internal jumpers- -one of which
would allow you to playback [FORMAT 1] (35mm/Mono) in either just the C channel, or
send it to L-C-R. -and there was a 2nd "MONO ENHANCE" jumper setting that would
create a 2-channel psudo-stereo (their words) output from a 35mm mono soundtrack.
I never actually tried the "ENHANCE" setting, it, so I don't know how well it worked.
I still occasionally work at one screening room that has a CP-45, but they rarely run film any
more, and it would be even rarer to run mono there. But it would be interesting to try if I ever
gettachance.

The CP-45 Also Had A Jumper To Do Matrix Decoding On The N-S Input
CP-45_Jumpers.jpg

[Mike Blakesley]

Thanks everyone for the info - lots of good info here.

I have a blu-ray of a concert by The Alan Parsons Live Project that has actual 5.1 sound on it. I converted that for my own pleasure since I am a Parsons fan. It is pretty cool to watch that in the theater with the sound cranked up. The audience sounds are mostly in the surrounds. It's a really nice mix, in fact my only complaint was the audience wasn't loud enough.

Another one I converted for my own use is "Pulse" by Pink Floyd, a terrific concert film from the '90s. This one is only L-R sound, sadly. But it still sounds really good. And of course being Pink Floyd, the visuals are just as great as the music is.

The movie that we had a request for that prompted this thread was Edward Scissorhands. I took a look at the blu-ray (inexplicably) and found that it has L-R sound. But before I even had a chance to ask about booking it, I noticed that it's a Fox film, so it's owned by Disney and hence "unbookable." But this thread will help in case another L-R movie comes up in the future.

[Brad Miller]

Edward Scissorhands is a weird title, as it was L, C, R with mono surrounds and no sub. Most of the blu-ray releases have a DTS 4.0 track carrying this.

I would strongly recommend you always check www.blu-ray.com when about to buy a blu-ray for this purpose, as earlier versions of the blu-ray often only have a 2.0 LtRt track and later ones have the 5.1 "pro-logic'd" output as 5.1 (or it was specifically remixed as 5.1).

[Mike Blakesley]

Yeah, the BR I had belonged to the potential customer, and definitely had a few years on it. That's good to know, I never could figure that out why they made it that way. Maybe our old friend "F." could shed some light.