Back Surround Left and Right sound don't work with DCP created with DCP o Matic

[Kyuuten]

Hello, I work in a cinema where we have a room with 5.1 audio and another room with 7.1 audio.

Using Dolby CP750.

I suspected that the 7.1 room was not outputting sound in the BSL and BRL (back surround left and right) speakers.

So with the Matic DCP I created a test sound for each of the 16 speakers that the Matic DCP offers.

I attached an image to the email and colored the boxes that sounded green and the boxes that didn't sound red.

Speakers 11-BSL and 12-BRL have no sound.

On the last visit that a technician made here at the cinema, I asked him about this problem and wanted to show him that the speakers were misconfigured because there was no sound, he didn't even test any sound, he looked through the system even with his devices and said that everything was fine and that not every movie, even 7.1, comes out with audio in these speakers, only a few rare movies use sound in them.

But I've been working there for years and no movie ever comes out with audio from these speakers.

So I said that I had made the test sounds to test.

He immediately refused to test these sounds saying that they were not made to cinema standards, and that any video or sound made without cinema standards would not come out in these boxes. He seemed to me to be very lazy, moody and unwilling to fix the problem and just making excuses.

This left me confused because I trust the Matic DCP and I believe that the sound created by it to come out in the BSL and BRL boxes should have come out.

My question for you is, if the test audio that I made with the DCP o Matic for the BSL and BRL speakers didn't come out in the speakers, is it because the speakers will be unconfigured? Or does the DCP or Matic really not meet such cinema standards that the technician said exist?

[Carsten]

There are different ways to approach this - the easiest is probably to use the 'official' Dolby 7.1 test DCP for this specific technician.
But of course, DCP-o-matic is able to create perfect test DCPs to all cinema standards.


First of all - you have to make sure that the cinema processor actually is in 7.1 mode when you play a 7.1 DCP. Second: A properly configured system has to output sound through the Back Surrounds even when in 5.1, just that they receive copies of left and right surround.

While 7.1 movies may be rare, those that we receive DO have actual and individual signal in the back surrounds. Creating a 7.1 DCP in addition to a 5.1 DCP costs money, and no studio is willing to pay for unnecessary expenses. Shortly put: This 'technician' talkes a lot of BS, and obviously is an idiot.


There are a few caveats when setting up and using a 7.1 system, from cinema audio processor setup, to amp and speaker wiring, to control cues between server and audio processor to switch between 5.1 and 7.1. If you don't find a useful technician, you probably need to check these items yourself.
Can you supply a picture of your audio rack, showing processor, and all amplifiers? There are detailed instructions for the CP750 towards proper 7.1 operation.

https://drive.google.com/file/d/14INWzY ... sp=sharing

- Carsten

[Kyuuten]

There are different ways to approach this - the easiest is probably to use the 'official' Dolby 7.1 test DCP for this specific technician.
But of course, DCP-o-matic is able to create perfect test DCPs to all cinema standards.


First of all - you have to make sure that the cinema processor actually is in 7.1 mode when you play a 7.1 DCP. Second: A properly configured system has to output sound through the Back Surrounds even when in 5.1, just that they receive copies of left and right surround.

While 7.1 movies may be rare, those that we receive DO have actual and individual signal in the back surrounds. Creating a 7.1 DCP in addition to a 5.1 DCP costs money, and no studio is willing to pay for unnecessary expenses. Shortly put: This 'technician' talkes a lot of BS, and obviously is an idiot.


There are a few caveats when setting up and using a 7.1 system, from cinema audio processor setup, to amp and speaker wiring, to control cues between server and audio processor to switch between 5.1 and 7.1. If you don't find a useful technician, you probably need to check these items yourself.
Can you supply a picture of your audio rack, showing processor, and all amplifiers? There are detailed instructions for the CP750 towards proper 7.1 operation.

https://drive.google.com/file/d/14INWzY ... sp=sharing

- Carsten

I'm just a low-level employee. I don't have full access to the setup software.
Just basic Web Commander access to create and play Shows.

[gunnar]

From what server are you playing the DCP? Are you trying to get the 7.1 sound via the Non-Sync input?
I am wondering if you are using dci compliant cinema equipment or not.

Properly configured dci compliant system should not have any problem with this. And remember, when you are playing 7.1 content you must run the processor in 7.1 mode.

[Kyuuten]

I have little technical knowledge about equipment names.

Would this be the server? Barco ICMP-01.1
Model projector - DP2K-10S

I play the DCP video that I ingested on the machine. It plays directly from it is not on the non sync channel. It's on Digital 1.

I have only acess via Web Commander.

[Carsten]

That's all okay. Can you supply pictures of the CP750 Display with each of the digital Inputs buttons pressed? It should say which format it is decoding.

For 7.1 vs. 5.1, there must be specific cues on the server to switch between the two (it is not automatic, you have to program a 7.1 CPL, and have the suitable 7.1 cue in the playlist), but they should also be available through the push buttons on the CP750.

- Carsten

[Kyuuten]

this is when a 7.1 movie is playing. I left the volume down just for testing.

I didn't find any CUE related to 7.1

My web commander login access is extremely basic. Does not give access to create new CUE.

But now I'm already satisfied. I wanted to make sure the technician did a terrible job here. And that left without working the BSL and BSR.

Thanks for the clarification you gave me.

[jdent02]

Yeah your technician sounds like a bit of an a*hole.

'Discrete' on the front display is 5.1 mode (see how there's only six 'bars' in the display). 7.1 would say "N/A".

But like Carsten said even in 5.1 mode you should hear something from the back surrounds if they are wired correctly. Sounds like they aren't.

[IoannisSyrogiannis]

Don't forget that between the Dolby CP750 and the speakers, there are amplifiers (cables, etc.)
Did you try (with the help of another) to check if you have some input (other source) on the Lbs and Rbs, what happens in the auditorium?
(If you connect a radio or something.)
Did you check what is the input going to the relevant amplifiers? If you change the inputs between Ls and Lbs, what happens? Do you hear the Ls audio out of the Lbs speaker(s)?
Do the amplifiers for the back surround ever peak? Do the side surround ever peak? When they do, is there any visual sign on the amplifiers?
Did you check, between the AES/EBU RJ45 outputs of the server and the DB25 input of the audio processor, how many cables are running? If it is one or two?

[...]
I'm just a low-level employee. I don't have full access to the setup software.
Just basic Web Commander access to create and play Shows.

Well, regardless of your employee level, you might have been able to get access to a linux terminal on the network of the booth and return the following commands:

Code: Select all

echo “cp750.sys.pcm_2_channel_decode_mode_1 4_discrete_sur”$’\r’ | nc put-the-IP-of-the-CP750-here 61408

echo “cp750.sys.pcm_2_channel_decode_mode_1 lr_discrete”$’\r’ | nc put-the-IP-of-the-CP750-here 61408

And see if anything happens.

Yet, I am not partial to your goal.

But now I'm already satisfied. I wanted to make sure the technician did a terrible job here. And that left without working the BSL and BSR.

It might be as jdent02 says, that they sound a bit... malevolent, but every cinephile that has seen "Rashomon" will agree that there is never only one story to tell...
All of us, keystrokes from the hyper-space, are not tangible proof for anything. You won't confirm or disprove anything from a discussion online. You will just get some responses, depending on what each of us has in mind, based on what you wrote.

[Carsten]

These amps have no signal indicators. They are not even labeled. Every amp has his own power switch.

First step: Prepare stickers for every amp. Play the Dolby channel test DCP. Cycle through each amp with the power switch, find out which amp carries which signal, and label them properly. I would assume that the channel assignment for these 2channel amps is:

Left/Right
Center/Sub( LFE)
Left Side Surround/ Right Side Surround
Left BackSurround/Right Back Surround

Also I guess that the only ZX 1000, the second amp from the bottom, is Center/Sub(LFE)

Once they are labeled, it is easier for you to switch them on and off as needed to find out what is actually going on.

These amps do have a range of inputs at the back, and it would be easy to feed a test signal (e.g. from your smartphone, if it still has an earphone/headset output) to the back surround amps to find out wether they do work and wether they are wired to the actual back surround speakers.

http://www.audiorama.com.br/unic/unic_Z ... manual.pdf

All that, of course, only if you are ambitious enough to dig into these technical things. If not - simply play the Dolby 7.1. channel test DCP to your boss, or the tech on his next visit. Someone paid for this equipment. He or she should care wether it works as intended. Make your boss tell the tech what to do.