Film-Tech Forum ARCHIVE: Audio Channel Mapping Glitch with GDC SX2001 and CP-750

This is topic Audio Channel Mapping Glitch with GDC SX2001 and CP-750 in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Justin Hamaker (Member # 2165) on 11-18-2014, 10:48 PM:

We had this happen at two different locations over the last two days, and it involved different titles in both cases.

Basically something happens which caused the VIN track to be routed to the sub. But this happened mid-week when there had been no changes to content, and no one had been messing with the configuration.

In both cases everything played fine for the first show of the day, then the issue happened during the second show. Because I am not able to replicate what happened, I don't know if it started in the pre-show, trailers, or feature.

The first location the first show was St Vincent, and the second was Fury. Fury was the show which had VIN coming through the sub.

At the second location it was Big Hero Six for the first show, and Interstellar was the second. Interstellar was the show which had VIN coming through the sub.

In both cases the auditorium is a GDC SX-2001 with a Dolby CP0750. The GDC at the first location is software version 8.142. The second location is version 8.156.

Looking at the channel mapping for the first location, the Interop tab 6-16 channels were set to 5.1 with HI/VI-N. In this set up inputs 11-12 were mapped to channels 7-8, and input 7-8 were mapped to 11-12.

For the second location, all the Interop presets were set to default, and for default all the inputs are mapped to the same channel (1=1, 2=2, etc).

I wasn't on site at the first location, so I can't exactly report what happened when testing. But at location two, I stopped playback of Interstellar and started playback of Big Hero. The issue with the VIN on the sub was present in this instance, where it hadn't been present during the first showing of Big Hero.

I changed the channel mapping so the Channel 8 was 5.1 HI/VI-N, saved and played. Issue was still present. I changed back to default, then rebooted all equipment. When I restarted the issue was gone.

As I said, both auditoriums ran fine all weekend with same program, and this issue has never happened before at either location in any auditorium.

The only common thread I can find is that Fury and Interstellar are both 4K content, where St Vincent and Big Hero are 2K. All four shows were 5.1 titles.

The only other thing is that the auditorium at location 2 is set up to play 7.1 when available.

Posted by Steve Guttag (Member # 268) on 11-19-2014, 02:04 AM:

I'm curious...did either SPL have any SMPTE CPLs? Note GDC current build for 8.01 is 186.

The only places we have ever had this sort of compliant was at a GDC site over a year ago with 2000AR systems...that was many firmwares ago though.

I tend to believe it isn't the CP750 since something has to be feeding it the HI/VI-N channels...in your 7.1 theatre...those channels are either not normally going into the CP750 or are going into "Digital 2"...I have never heard of Digital 2's input getting out of the main outputs when in 7.1 mode. We also have many, many CP750s and while not glitch free, I cannot think of a situation where we've had the problem you described that wasn't with a GDC. Since the GDC can map channels, it can also make a mistage. Note the CP750 can map channels too...but those channels have to be there to be mapped and they shouldn't be on the 7.1 theatre.

With SMPTE content, the content maps itself (note in the GDC set up you have Interop mapping as well as SMPTE). I have found strange happenings on mixed Interop and SMPTE shows...things that have seemingly affected subtitles and/or audio. Hence I'm curious if your shows are mixed.

Posted by Justin Hamaker (Member # 2165) on 11-19-2014, 03:21 AM:

I don't see anything with a SMPTE notation in the CPL. The features all have IOP, and some trailers have either IOP or INT.

Posted by Marcel Birgelen (Member # 6801) on 11-19-2014, 03:45 AM:

I agree with Steve that the CP750 is not the most likely culprit, especially because it happened at two different locations. It's also hard to imagine something in the AES bit streams capable of triggering this and like Steve already mentioned, none of the HI channels should be on the main digital input (Digital 1) in the first place. But still, try to first reboot the CP750 and check if it remains, before you reboot your server.

If the issue is still present after you power cycled the CP750, you can at least get the decoder itself off the list.

Posted by Steve Guttag (Member # 268) on 11-19-2014, 06:44 AM:

Do you have any "home grown" content? Policy snipes or ads? DCP O Matic defaults to SMPTE though you can select Interop. Thus far, except for ATMOS titles, Hollywood has been pretty consistent with IOP for features and trailers (I don't recall, Hobbit may have been SMPTE...but I guess I'll see soon enough...or it may have been the HFR Hobbit).

You can always pull the logs of the server right after the incident and submit them to GDC...try to be as specific as possible on the date/time. GDC can be most helpful (they have to be since they don't make their logs extractable except by them!). If there is a problem with their software, they'd want to make that fix. Naturally, you can try updating to the most current firmware (they'll probably suggest that as a first step).

Posted by Jason Raftery (Member # 6291) on 11-20-2014, 12:05 AM:

I've experienced the same exact mysterious channel routing problem with VI going to the subs with Interop DCPs on GDC SX-2000AR servers (a rare, but ongoing issue for my circuit on builds through 287) but not with the 2001's. If the problem is going to occur, it usually shows up on the first show following a power cycle of the server/IMB. Trailers apparently play fine but once the server hits the feature, we encounter channel routing errors (usually involving VI/sub or center/sub).

Power cycling ONLY the projector/IMB has resolved the issue in every case. Additionally, we have yet to see the issue strike the same house more than once, even many months after the previous occurrence.

For reference, my sites have Interop channel routing set to Default for all pairs on the GDC.

I second Steve's suggestion of contacting GDC and providing logs. It's very interesting to hear the issue can also occur on non-IMB machines.

Posted by Monte L Fullmer (Member # 2797) on 11-20-2014, 01:11 AM:

Had that issue also with a CP750 with VIN coming through the SUB channel in one of my houses.

Did a full system cold reboot of projector, server (SX-3000 IMB along with the PSD-3000 storage unit) along with processor which cleared the issue.

Had a bad case of "brainfarts" for a while.

-Monte