Film-Tech Forum ARCHIVE: Problem Using DTS 6AD External 6ch Input

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Posted by Jeremy Weigel (Member # 4208) on 05-09-2009, 12:09 AM:

We recently converted 2 screens to digital (Real D). We are using GDC servers and running the audio first through a USL DAX-602 D/A converter then into the DTS 6AD 6CH External input on one of the machines and a CP500 on the other.

The problem I have is that the left channel sounds noticeably louder than the center and right on playback with the 6AD. I've checked the SPL using the internal pink noise generator of the 6AD and all levels and EQing are checking out spot on. I have also run the Empirical Test disc and it checks out. For the time being I have lowered the SPL of the left channel so that playback sounds "balanced" to compensate for now. Unfortunately there are no audio test files such as pink noise on the GDC.

Has anyone else encountered a similar problem?

Posted by Demetris Thoupis (Member # 833) on 05-09-2009, 12:33 AM:

The USL DAX-602 D/A has a fixed output at 300mVrms reference level BUT it is adjustable via a computer software. I am sure Clint can inform you more. Is there a chance by some "cough cough trimming cough cough" someone messed it up?
Demetris

Posted by Jeremy Weigel (Member # 4208) on 05-09-2009, 12:58 AM:

I think I pretty much ruled out the D/A converter since I swapped it with the other one that's connected to the CP500 and the issue remained.

Posted by Demetris Thoupis (Member # 833) on 05-09-2009, 02:20 AM:

Well as I said before, there is a software to trim the audio output from the USL unit to trim the left channel down should you wish too.
Demetris

Posted by David Zylstra (Member # 4230) on 05-09-2009, 11:25 AM:

I found that we had almost this exact same problem with the DoReMi analog output plugged into our 6AD inputs.

I would suspect your connecting cable is wired wrong - the DTS 6AD uses specific pins for the low (-) side of each channel's signal with only 1 ground pin but the Dolby has unbalanced input and ties all unused pins to ground (manuals for both units are in the "Manuals" section - take a look at the differences in input pinout).

It took our service provider/installer 6 months to find and ship the right cables (they shipped the wrong ones twice) - I ended up modifying their original cables with the correct pinouts myself to prove what the issue was.

Posted by Pete Naples (Member # 761) on 05-09-2009, 12:11 PM:

quote: David Zylstra
It took our service provider/installer 6 months to find and ship the right cables

Does no one own a soldering iron anymore?!

Posted by Louis Bornwasser (Member # 3063) on 05-09-2009, 03:31 PM:

Not in America (except us!) LOuis

Posted by Steve Guttag (Member # 268) on 05-09-2009, 05:26 PM:

See...there you go...thats the problem...soldering the Dsub instead of crimping.

I know for many of the "alternative content" companies we deal with...we tell them to just skip the cables...we'll take care of that...way too many bad cables. Same goes for the DCinema cable companies. I don't know if they still do, but DoReMi was using analog audio cables instead of AES audio cables (difference impedence).

Dolby tells me we are the only ones that make our own Dolby Digital Reader cables...I find that strange and sad, if true. They are not that hard and one then only uses as long a cable as needed and it can be dressed properly in conduit/greenfield/liquidtight.

Steve

Posted by Mark Gulbrandsen (Member # 72) on 05-09-2009, 07:56 PM:

quote: Louis Bornwasser
Not in America (except us!) LOuis

Ha! I even own(personally)Surface Mount de-soldering/soldering gear!

DAX works via NETBIOS so if you have that configured on your laptop all you should have to do is type "DAX" in your web browser and the setup program will come up via the ethernet port. There is an alternative IP address(try 169.254.1.123 according to the manual) use with a cross over cable but DAX works on my laptop.

We manufacture all of our own cables too and I agree with Steve.... probably an improperly made up cable. I don't agree that its bad to solder cables though, For years I've used a special silver alloy solder on my cables and I'd claim its actually better than crimps. You won't fnid a single crimped connection in any of the Space Shuttle hardware!! It just takes an experienced tech to do it right. It pays to hire a good service organization to install stuff like this... Not the Wrong Company!

Mark

Posted by Steve Guttag (Member # 268) on 05-09-2009, 09:59 PM:

Solder has its place and I do a lot of it. On DSubs...I find crimps to be superior. They are faster and generally will do a better job of conducting.

Steve

Posted by Jeremy Weigel (Member # 4208) on 05-10-2009, 01:16 AM:

Thanks for the input guys. I'll make up a new cable between the DAX and 6AD to replace the one that the install team used as well as hook up a laptop to the DAX. The company that installed the equipment has been told by GDC that they (GDC) are working on creating the audio test files.

Posted by Mark Gulbrandsen (Member # 72) on 05-10-2009, 01:53 PM:

quote: Steve Guttag
I find crimps to be superior

I guess if NASA also found them superior they'd be using them too!

Any MXF file should play back just fine on the GDC. No need to wait for them....

Where is SMPTE during all this. They SHOULD be supplying both aural and vuisual test files for D-Cinema.

Mark

Posted by Julio Roberto (Member # 4976) on 05-10-2009, 03:17 PM:

Perhaps this could be of help. It's not designed for what we want here exactly, but may be of some use to some for similar purposes.

http://www.dcimovies.com/reference/
[link is to page from DCI on how to order their DCI reference package in a disc and how to obtain a KDM for playback of the cyphered part on your server]

Posted by Gordon McLeod (Member # 33) on 05-10-2009, 04:09 PM:

Test material should not require a key but a one time purchase of the material and it should be available from SMPTE like other test material

Posted by Julio Roberto (Member # 4976) on 05-10-2009, 06:15 PM:

I believe the test material includes both, unencrypted and encrypted content. The encrypted content is to test the (working) decryption on your server. The key delivery message is generated on-line, so you can have easy access to it when you want for any server. I believe it doesn't expire once you have it.

If you don't have access to any other test material and don't know how to create your own, it could be a sensible route to go.

As I said, it's neither perfect nor designed for what we are talking about here, but it could be useful under similar circunstances.

For only $18 for a disc, I say it's worth it for a lot of us to have around. At least we know the content itself is carefuly made to specs (which our equipment may not follow, but nonetheless).

Posted by Jeremy Weigel (Member # 4208) on 05-25-2009, 02:52 PM:

Made a custom cable to connect the DAX to the 6AD. Just so happens that the screen alignment test for UP has channel ID with pink noise bursts that I was able to use to gauge playback levels.

The center and right are still about 4dB lower than the left. I also connected my laptop to the DAX to make sure that internal gains are at zero. I went ahead set the center and right to match the left via the 6AD.

Posted by Jeremy Weigel (Member # 4208) on 07-11-2009, 07:56 PM:

When making this cable between the D/A converter to the DTS should I have all the shields on the 6AD tied together on pin 13 (analog ground) and the shields going to one each one of the grounds on the D/A converter? Or should I only connect at the D/A converter side?