Film-Tech Forum ARCHIVE: No sound on Left and Right channel on Dolby CP750

my profile | my password | search | faq & rules | forum home

»	Film-Tech Forum ARCHIVE » Operations » Digital Cinema Forum » No sound on Left and Right channel on Dolby CP750

Author

Topic: No sound on Left and Right channel on Dolby CP750

Justin Hamaker
Film God

Posts: 2253
From: Lakeport, CA USA
Registered: Jan 2004

posted 03-06-2015 09:45 PM

This issues just started today. I don't have any sound on left and right channels in one auditorium. This appears to have just started today. I have checked all of my cabling to look for loose connections.

Discovered the issue when we had customers complain of no sound during our preshow (which I believe is just L/R). During trailers and the feature the L & R channel is completely flat when I look at the eq on the Dolby software.

I ran the Hollywood Sound Test and definitely did not have audio in the L or R channel. But did have LS, RS, C, and SW.

Using the Dolby software, I swapped the inputs for the R and C channels, and the sound followed.

Any ideas?

| IP: Logged

Stephan Shelley
Jedi Master Film Handler

Posts: 854
From: castro valley, CA, usa
Registered: Nov 2014

posted 03-06-2015 09:51 PM

Do you have left and right with non-sync. Also check with pink noise. If you have it with those but not from the media block L/R are one AES pair. Check cable/connections between media block and the 750. It is also possible there is a problem with the media block itself or the AES connector/input on the 750.

| IP: Logged

Robert Harrison
Expert Film Handler

Posts: 239
From: Harwood Heights, Illinois, USA
Registered: Jun 2005

posted 03-06-2015 10:03 PM

I have had this problem, also, and only with one unit (out of 4). In my case, I switch between discrete and pro-logic, depending on the material being 2 channels or 5.1. It happened this afternoon (again). My only recourse was to reboot the Dolby unit, which worked before. I'm going to do without the switching and leave the unit in discrete during presentations (this doesn't seem to occur in non-sync mode where I always use pro-logic). Must just be a glitch. Let's see if anyone knows of an update fix.

| IP: Logged

Justin Hamaker
Film God

Posts: 2253
From: Lakeport, CA USA
Registered: Jan 2004

posted 03-06-2015 11:43 PM

After restarting the CP750 the issue went away. What's interesting is all channels were working in non-sync before the reboot, so it would suggest the problem has something to do with the AES input, or the Digital 1 format.

| IP: Logged

Nguyen Jack
Film Handler

Posts: 93
From: Singapore
Registered: Mar 2013

posted 03-07-2015 02:00 AM

I Think you need to check cable connect. or change another cable.

| IP: Logged

Magnus Eriksson
Expert Film Handler

Posts: 121
From: Stockholm, Hägersten, Sweden
Registered: Jan 2011

posted 03-07-2015 04:49 AM

There is an issue with the non-sync input. From release notes:

"Switching to the Non-sync input while configured for format 71 (Mono C), can sometimes result in distorted audio output. The CP750 must be restarted"

"Distorted" in my case meant a messed up channel mapping and/or muted channels when playing AES/EBU. A CP750 reboot fixed the sound for a day or so.
Changing the non-sync input from mono C to prologic solved the problem permanently.

| IP: Logged

Justin Hamaker
Film God

Posts: 2253
From: Lakeport, CA USA
Registered: Jan 2004

posted 03-07-2015 05:09 AM

Mangus, that does not apply to my situation. First of all, the movie was not in 7.1. Secondly, the issue was not missing channels in non-sync, it was missing channels in Digital 1.

| IP: Logged

Magnus Eriksson
Expert Film Handler

Posts: 121
From: Stockholm, Hägersten, Sweden
Registered: Jan 2011

posted 03-07-2015 05:23 AM

quote: Magnus Eriksson
messed up channel mapping and/or muted channels when playing AES/EBU

Sorry for my Swedish [Wink]

This was a 5.1 setup, the problem occured when the CP750 switched from non-sync to Digital 1.

| IP: Logged

Dave Macaulay
Film God

Posts: 2321
From: Toronto, Canada
Registered: Apr 2001

posted 03-07-2015 08:28 AM

The obvious place to look is in the 4xAES cabling since L+R is on one AES stereo signal.
That also means one D-A converter in the CP750 is handling the L+R conversion so it could be the processor.
Rebooting clears up some CP750 issues but it's not prone to that kind of problem.
It could also be a server fault
In my experience "missing one AES pair" problems have been caused by the cabling between server and D-A converter.
A marginal signal can work sometimes and not other times.

| IP: Logged

Jim Cassedy
Phenomenal Film Handler

Posts: 1661
From: San Francisco, CA
Registered: Dec 2006

posted 03-07-2015 08:52 AM

A couple of weeks ago, I had the VI track coming out of the subwoofer.

Re-booted the 750 and the gdcdigitalcinemaserverthiny and it's
never happened again.

Remember, digital cinema is not an 'exact science'.

Sometimes stuff just happens.

| IP: Logged

Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 03-07-2015 10:47 AM

The most likely culprit is the cable/connectors/adapters on pair 1.

As for the VI out of subwoofer...that is a known GDC problem...rebooting just the GDC server would have "fixed it."

| IP: Logged

All times are Central (GMT -6:00)

Printer-friendly view of this topic

The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion and agrees to release the authors from any and all liability.