GDC SR-1000 Stuttering During Playback

[Chris Haller]

Folks,

We have GDC SR-1000 IMBs handling CPL playback and audio processing for all of our houses except house 8 of our 9 screen theater, which has a Dolby CP 950 handling a Dolby Atmos audio stream. It seems to happen at least once every big release on a couple screens, in front of a huge sold out shows of course, that during the movie we get a few stutters during playback - in this case I was watching Wicked in house 8 with a paying audience and it of course stuttered during the climactic "Defying Gravity," sequence.

I've taken over the programming of our theater's TMS since late September, and I feel like I'm pretty on top of maintaining our software and hardware - I keep storage space cleared of old movies, do weekly hardware reboots, and have our technical service providers maintain the most up to date, tested firmwares for our NEC 1202L and 1402L projectors and SR-1000s. Haven't seen a stutter in ages on pretty much anything, so I'm mystified as to why it came back.

Has anyone here experienced this before? Should I just brace to live with this every now and then for the rest of the time they're in deployment?

[Steve Guttag]

Stutters/pixelations are almost always drive related. However, you indicate that there is an Atmos aspect to it all. It could still be drive related because for the CP950A to get the audio, it has to be streamed to it via Ethernet and GDC, on the SR1000, comingles the audio streaming with other network since it only has 2 NICs. Normally, one wants media on its own NIC since content transfers use as much bandwidth as you have and it still can take 1-hour or more to transfer content. Management gets a NIC for control/UI type stuff. With Dolby Atmos, you need to get the Atmos track to the CP950A. I believe that they have you use the management NIC/network convey the Atmos content to the CP950A for processing. So, it is up to the SR1000 to keep that pipeline full. Furthermore, there needs to be a Sync between the server and the CP950A so that the track and picture are kept in sync. This is on AES tracks 13/14 (pair 7). This is one reason both AES3 connectors have to be connected between the host server and the CP950A...One reason is for backup 7.1 (pairs 11/12) and the other is for the sync track (13/14).

So, your potential problems are:

• SR-1000 isn't keeping up with streaming the audio (buffer underflow).
• Management Network isn't moving the stream to the CP950 command port adequately.
• SR-1000 firmware isn't on a good version for Atmos (check with GDC).
• CP950A just got a new version 2.3.2.5, make sure you are updated to it. It's all good, from what I've experienced.

I would pull logs from both the SR1000 and the CP950A and submit them to their respective companies with an accurate date/time of when the stuttering happened so they can look for where the data was having issues. Based on what they say, you can attack the problem.

[Chris Haller]

So, your potential problems are:

• SR-1000 isn't keeping up with streaming the audio (buffer underflow).
• Management Network isn't moving the stream to the CP950 command port adequately.
• SR-1000 firmware isn't on a good version for Atmos (check with GDC).
• CP950A just got a new version 2.3.2.5, make sure you are updated to it. It's all good, from what I've experienced.

I would pull logs from both the SR1000 and the CP950A and submit them to their respective companies with an accurate date/time of when the stuttering happened so they can look for where the data was having issues. Based on what they say, you can attack the problem.

We've pulled the SR1000's logs, though I will double back and pull the CP950A's logs as well. You know, it didn't even occur to me that it would have its own firmware and data transfer limitations. I will seek out the Dolby update as well - it almost always stutters in the Atmos house, though occasionally does it our other houses as well that use the SR-1000's built in processing capabilities.

Thank you for your input. I was given like 2 hours of training the night they passed responsibility on to me and I have learned a LOT about Digital Cinema in the last two months. Lord there's a lot going on up here in my booth. It's very engaging work, but having to trip over land mines to learn pretty much everything I've learned so far has been a little irritating.

[Leo Enticknap]

Agreed completely with Steve, which is why, if I have any input into equipment purchase decisions, I would advise against an SR-1000 for an Atmos house. That having been said, the Barco Alchemy/ICMP also sends Atmos data through the management LAN due to only having two NICs if the second is used for media, and I've never had any trouble installing an Alchemy for Atmos playback. But I have, at multiple sites, with the SR-1000.

On the CP950A 2.3.2.5 upgrade, note the warning in the release notes: apparently, if you try to install it after the processor has been running for a long time without a reboot, it can bork it completely. So the safest approach is to power cycle it immediately before installing the update.

[Ryan Gallagher]

A coworker saw Wicked at a local Regal laser house. Not sure if it was Atmos, but she said the film started in full surround and then two minutes in dropped to mono center only, and stayed that way for the rest of the film. Ooooof

[Leo Enticknap]

That's weird. Several audio processors have an emergency mode whereby if there is a problem with the center channel (an amp channel fails or a speaker driver blows, basically), it will apply the center channel's signal equally to left and right, so that you don't lose dialogue playback on a 5.1 or 7.1 mix. But I can't think of a failure mode that would mix everything down to 1.0 center, unless what's what the bypass mode on older Dolby processors does (I've never actually tried it)

[Marco Giustini]

The PCM track behind Atmos is usually 7.1 but it can be 5.1.

if the track turned mono, it's not because Atmos dropped! On a good sound system if Atmos drops to 5.1 or 7.1 it won't be a "booo" event! Most people wouldn't even notice, particularly with some movies where atmos objects are barely used.

[Steve Guttag]

...That having been said, the Barco Alchemy/ICMP also sends Atmos data through the management LAN due to only having two NICs if the second is used for media, and I've never had any trouble installing an Alchemy for Atmos playback...

"Mr Leo"...I have questions (well a question). The ICMP-X has two NICs but it uses the projector's router/switch for its "management," which leaves both NICs available to be assigned for other uses, no? One for the Media, naturally. It isn't like the ICMP series is a ball-of-fire on content transfers anyway. Why can't the other one be used for dedicated Atmos streaming?

The ICMP is my least used (of the servers I support) and I, currently, have zero in Atmos applications.

[Gordon McLeod]

Were you transferring or ingesting content when it started to stutter

[Chris Haller]

Were you transferring or ingesting content when it started to stutter

Nope. Clean as a whistle in that department.

[Marin Zorica]

"Mr Leo"...I have questions (well a question). The ICMP-X has two NICs but it uses the projector's router/switch for its "management," which leaves both NICs available to be assigned for other uses, no? One for the Media, naturally. It isn't like the ICMP series is a ball-of-fire on content transfers anyway. Why can't the other one be used for dedicated Atmos streaming?

The ICMP is my least used (of the servers I support) and I, currently, have zero in Atmos applications.

ICMP second port is used for atmos stream to processor, while first is used for content ingest. I have newer did use projector lan to send atmos data to processor.

[Steve Guttag]

That makes sense to me...hence my question to Leo.

[Ryan Gallagher]

That's weird. Several audio processors have an emergency mode whereby if there is a problem with the center channel (an amp channel fails or a speaker driver blows, basically), it will apply the center channel's signal equally to left and right, so that you don't lose dialogue playback on a 5.1 or 7.1 mix. But I can't think of a failure mode that would mix everything down to 1.0 center, unless what's what the bypass mode on older Dolby processors does (I've never actually tried it)

That may have been what she heard. She said single channel from front... but it may have been coming out of L+R... but the noticeable bit to her untrained ear was the loss of surrounds apparently. So that doesn't seem like merely a Center failure mode. I could also see being duped by the mix in the first dialog scene, but not if it stayed that way the rest of the film even for the big sequences.

But anyway, was just an side story. Not relevant to this issue.

[Leo Enticknap]

With an Alchemy in a Series 2 projector, access to the web UI via the projector's NIC is OK, but I've found that sending API commands via that route is often laggy and sometimes fails totally. Therefore, LAN A on the Alchemy has to be used for management, plus Atmos if LAN B is needed for media. This is not so much of a problem with Series 4.

[Steve Guttag]

Interesting. Have you noticed any difference between 1st generation and current generation CCBs for S2s? It may be me but I'm noting that the current CCBs seem to have more fussy DVI ports (at least getting a picture to the ICP).