Film-Tech Forum ARCHIVE: Audio Crackling DSS220 CAT745

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Posted by Peter Maddock (Member # 7652) on 02-10-2014, 08:33 PM:

We have been experiencing severe intermittent crackling in our Dcinema system which is currently 5.1 although soon to be 7.1.
The projector is a Barco DP2K 10S with Dolby DSS220, CAT745 IMB, and Dolby CP750.
The problem can generally be corrected by manipulating the AES Audio Ethernet connection to the CP750. We have resorted to supporting this cable with masking tape to reduce the interference.
Our installer says our upgrade to 7.1 should overcome the problem however we will then be using two Ethernet audio cables between the IMB and CP750, which seem to be the source of the problem.
We are a single screen community cinema. Installer says the Dolby system has been installed in multiplex chains without problems.
Anyone experienced this problem.

Posted by Jason Raftery (Member # 6291) on 02-10-2014, 10:06 PM:

Does the CP750 display show the word "Discrete" intermittently dropping out as the crackling is occurring?

Replace the Ethernet cables running from the IMB to the CP750--one or both of them is likely bad.

Posted by Carsten Kurz (Member # 5396) on 02-11-2014, 08:45 AM:

Yes, there have been a few reports of bad ethernet-audio cables on this forum earlier. How long is the connection between the projector/IMB and the CP750?

Best is to convert to proper AES cabling as soon/short as possible.

- Carsten

Posted by Dave Macaulay (Member # 813) on 02-11-2014, 11:00 AM:

What do you use at the CP750 to go from ethernet to DB25? The Odyssey RJ-DB card has been good for us, and the 7.1 channel swapper card version does that job well. Plus, using high quality premade CAT6 cables is our normal practice: we have seen many problems because of faulty field termination of ethernet cables.
We have not had any issues with the AES over CATx approach and I don't personally believe using "proper AES cables" will make any difference. You have some problem not inherent in using CATx cabling.

Posted by Sam D. Chavez (Member # 1841) on 02-11-2014, 04:55 PM:

I've also had good luck with the Odyssey kit. AES cable is best for long runs though but expensive and not particularly convenient in this plug and play world where a lot of techs don't carry a soldering iron. (Probably for the best [Big Grin]

Posted by Peter Maddock (Member # 7652) on 02-11-2014, 05:21 PM:

We have 10m of Ethernet cable between the DSS220 and IMB. We went for the Dolby system as it enabled connection to our remote projector which is mounted outside our bio box. The Doremi required a much shorter PCI Express cable.

I am picking up a 7.1 card from the installer today and will speak to him about AES cabling.

The Ethernet cable is connected to the CP750 via a RJ45/D25 adapter plug supplied by the installer.

I am sure there would not be an inherent design problem with the Dolby Ethernet data connections.

Thanks for the feedback on this problem.

Peter

Posted by Mark Gulbrandsen (Member # 72) on 02-11-2014, 05:24 PM:

I used AES up to about a year or so ago but use CAT 6 now in just about all installations. Not one issue and I have runs up to 30 feet long.

Mark

Posted by Carsten Kurz (Member # 5396) on 02-11-2014, 05:27 PM:

We have a few discussions on the forum about this. While in general, CAT5-7 is suited for AES audio cabling, it seems that in real world scenarios it sometimes causes trouble, either by bad cables, screening, or simply the cable run is too long and the connected devices do not follow AES specs strictly . I also learned that large parts of the world still use unscreened twisted pair.

As you now came up with a 10m run, I'm sure this is the problem. You may try a different/better cable, or switch to a different converter/cable combo as suggested by others. If you go 7.1., the dedicated Odyssey board with selectable signal routing for 7.1 and HI/VI is probably the best solution.

- Carsten

Posted by Marco Giustini (Member # 4544) on 02-11-2014, 05:37 PM:

Despite the Ethernet not being the best for AES, the 745 does not have any issues with the it.
If you have crackling noise you should replace your AES cable immediately - or check the connector, I guess the soldering may be faulty.

You could install the ethernet cables straight away without waiting for the 7.1 upgrade.

Posted by Sam D. Chavez (Member # 1841) on 02-11-2014, 07:12 PM:

The Odyssey Ethernet kit comes with two 35 Ft. Cat. 6 cables and I've had no problems with using that length but have not tried a longer run than that.

I do like the the AES breakouts boards and had a bit to do with the design but this method has fallen from favor due to cost and the aforementioned problem with knowing in advance what the cable length will be.

Posted by Harold Hallikainen (Member # 5405) on 02-11-2014, 08:19 PM:

EBU3250E - AES/EBU Interface, Third Edition, 2004. States AEA/EBU may be carried over CAT5 cable for 400 meters unequalized and 800 meters equalized.

Harold

Posted by Steve Guttag (Member # 268) on 02-12-2014, 04:40 AM:

I believe, in the US and probably other countries, AES must use screened cable (shielded) or it will cause RF interference.

We have had good luck with CAT cable for AES but also will still use proper AES cable, depending on the installation, environment, needs. We always make our own cables. I've had many more premade cable failures than our own.

Posted by Dave Macaulay (Member # 813) on 02-12-2014, 07:02 AM:

I tried an RJ-DB adapter unit, it had a bunch of jumpers attached to the RJ45 that I plugged into the DB25 side. It worked OK for a while then they had issues with lost channels. I put in the Odyssey basic adapter and have had no problems since. I don't know what adapter your installer provided, but that's where I expect the problem could be. Swapping cables would be my first try, then losing that adapter if the cable change doesn't help.
Doremi includes an adapter with their IMBs that I've used without trouble; it's just a pain because another cable has to be used to the D-A. The Odyssey card is simper and looks tidier.

Posted by Harold Hallikainen (Member # 5405) on 02-12-2014, 07:35 AM:

Of course, no adapters are required when driving a USL JSD-100 or JSD-60, since they have RJ45 AES/EBU inputs. Also, everyone agrees on the pin out of these connecrors, as opposed to DB-25.

Harold

Posted by Steve Guttag (Member # 268) on 02-12-2014, 01:16 PM:

Since we make our own cables...we just put on the DB25 right to the CAT cable...always works.

Posted by Peter Maddock (Member # 7652) on 02-12-2014, 01:16 PM:

I have just installed the Odyssey 16 RJ-7.1-DDSY adapter board provided by our installer and it looks better than the original RJ45/D25 adapter and as yet no problems with crackling.
Not set up for 7.1 yet but have a few extra cat6 cables ready in case we have more problems. Also waiting on installer to provide 7.1 test files.

The DSS220 manual says ensure the rack is well earthed. Installer says < 3 ohm DSS220 chassis to projector chassis. We have yet to test this; perhaps if we have more problems.

Cheers
Peter.

Posted by Marco Giustini (Member # 4544) on 02-12-2014, 04:03 PM:

Thanks Harold, I was looking for that information!

Posted by Peter Maddock (Member # 7652) on 03-05-2014, 09:48 PM:

We are still experiencing crackling problems after installing the Odyssey board. This is a very intermittent problem so it is driving us nuts.
Steve, you mentioned wiring cat6 directly to DB25, do you have a wiring diagram for this as apparently Dolby has not published this?

Posted by Harold Hallikainen (Member # 5405) on 03-05-2014, 11:22 PM:

This could be a problem in the IMB, the cable, or the CP750. I know you're looking at swapping the cable, but is there other stuff nearby you can swap, perhaps between auditoriums, to see which piece the problem follows?

I know that there have been problems with some content and forensic marking, but perhaps those issues have been solved. Also, I think you said there was an indication on the CP-750 that the AES was bad. I do not believe FM problems would show up as AES errors.

Good luck!

Harold

Posted by Pete Naples (Member # 761) on 03-06-2014, 02:24 AM:

I recently had a crackling issue with a similar setup.

I replaced AES cable, connectors at both ends, replaced CP750->amps wiring, re-made amp output connectors, went over rack mains and speaker terminations and re-made all the loudspeaker terminations in the cinema. It sounded like typical crackle from bad connections.

It was no better [Frown]

Eventually I traced it as coming from a hand dryer in the downstairs toilets!

Posted by Carsten Kurz (Member # 5396) on 03-06-2014, 05:02 AM:

Peter - can you give a rough estimate on how often and for how long the crackling occurs? The question is - does it happen more or less 'on its own', e.g. due to bad cabling or IMB/CP, or is it strongly related to other gear, e.g. Freezers, HVAC operation, etc.?

Do you have a chance to check the status/valid indicators on the CP750 when the crackling occurs?

A good common ground between projector/IMB and audio rack is important, although I don't know wether both CAT745 AES outputs and CP750 inputs are transformer coupled.

- Carsten

Posted by Harold Hallikainen (Member # 5405) on 03-06-2014, 07:12 AM:

I believe they are both transformer coupled.

Harold

Posted by Steve Guttag (Member # 268) on 03-06-2014, 07:25 AM:

They most certainly do. Look in the CAT745 installation manual (it is on line at Dolby's customer support web site...registration/authorization is required).

Posted by Peter Maddock (Member # 7652) on 03-06-2014, 12:45 PM:

Yesterday we had consistent crackling from the system. We did get some high resistances between the projector, audio rack and CP750; 20 + ohm. We have run some extra earth cables particularly between projector and audio rack and reduced to acceptable levels.
After noticing the influence of movement of the CP750 DB25 input plug on the crackling our installer advised us to route the AES audio from the IMB to our Gefen Scaler which on digital bypass goes to the CP750 Multi Channel Analog input. This seems to have eliminated the problem.
Our installer thinks there may be a problem with the CP750 input socket. We obtained this unit under warranty as a replacement for a unit which had a greyed display. This unit has the same display problem and our installer advises it may be a refurbished unit, not a new one.
Matinee screening this morning so hope all goes well!

Posted by Marco Giustini (Member # 4544) on 03-06-2014, 06:16 PM:

What Gefen scaler do you have which decodes 4xAES?

The "greyed" display is a known bug. If it's the one I'm thinking, just go to the contrast setting, move the value to whatever and the display will come back to life - till next time.

Posted by Peter Maddock (Member # 7652) on 03-06-2014, 07:02 PM:

We are using Gefen A/V Cinema Scaler Pro II.

Yes correcting the display can be done by 4 presses of the menu button to the contrast screen. Slight adjustment of the contrast restores the display then 4 more presses of menu gets you back to the main display screen.

Posted by Marco Giustini (Member # 4544) on 03-07-2014, 02:16 PM:

I did not remember the Cinemascaler pro II had an AES input, cool.

Yes, the issue you have is "normal". I suppose they'll fix it at some point but we haven't seen a CP750 FW for a while now.

Posted by Steve Guttag (Member # 268) on 03-07-2014, 04:53 PM:

The Gefen Proscalers II and III have both analog and AES inputs...one could place it at the head of any film Cinema processor with 5.1 or 7.1 inputs much the same as a DMA8 Plus or ECI-60 or DAX602

Posted by Peter Hall (Member # 695) on 03-10-2014, 11:53 AM:

HI
We've had similar crackling twice -
1. Where the original install had used Cat5 from a proprietary wall box to the CP. We replaced this with twin screened data cables x 4 earthed in the CP only and it worked a treat
2. A weird one, we ran a new set of screened AES cables from the DB25 adaptor through what was once the exciter lamp power supply conduit (now totally stripped and completely empty, and earthed to the rest of the building's containment). Channels 3 and 4 and 5 and 6 clicked and varied in level, sounding like something was charging up and breaking over (eg sound drops and drops and then CLICK and it is up full again). Measured it, played around to find the noise and eventually ran the cable externally and all was good.

Posted by Peter Maddock (Member # 7652) on 07-03-2014, 09:34 PM:

This is an update on this ongoing issue with intermittent audio crackling in our CP750, DSS220 system.
In desperation sometime ago we bypassed the Digital 1 input to the CP750 and routed the Cat6 from the IMB to our Gefen Scaler. The Gefen Scaler on Digital Bypass to Multi-Channel Analog input on the CP750 has enabled us to screen without the audio crackle for nearly four months.
Recently it appeared there may have been a problem with the 4XAES input socket on the CP750. To eliminate the RJ45 connection to the CP750, which has appeared to be some of our problem we soldered the Cat6 from the IMB to a DB25 plug.
On initial testing the crackle returned, perhaps confirming a problem with the input socket. However further testing, before sending the CP750 for repairs the crackle is not occurring.
I have uploaded a couple of short videos to you tube. The first one http://youtu.be/rlfqMNi13-0 is in our auditorium. The crackle comes through at the volume setting of the CP750 and the show playback audio is impossible to hear. In these two videos there is no show playback occurring.
The second video shows the crackle coming through when the CP750 is set on Discrete on the Centre and LFE channels. When the decode mode is switched to Pro Logic the crackle stops. http://youtu.be/0bKGc7fmVa4 I presume this is because Pro Logic decodes the left and right channels only.
So we seem to be back to chasing down a gremlin in our sound system!

Posted by Carsten Kurz (Member # 5396) on 07-04-2014, 05:44 AM:

With these videos, I would approach Dolby for a swap of the CP750, it should be under warranty?

- Carsten

Posted by Peter Maddock (Member # 7652) on 02-09-2015, 07:36 AM:

Yesterday we had consistent crackling fro the system. We did get some high resistances between the projector, audio rack and CP750; 20 + ohm. We have run some extra earth cables particularly between projector and audio rack.
Ae appeared to

Posted by Derek Martin (Member # 7657) on 02-09-2015, 08:41 AM:

We fixed a similar sound problem by replacing cat-6 cables and odyssey adapters with aes cable. Our problem started after a neighboring building was renovated and a transformer box installed for it in our parking lot, though that could be a coincidence.

Posted by Dave Macaulay (Member # 813) on 02-09-2015, 04:59 PM:

We had a bizarre site with nasty noise bursts in the server audio - on a schedule! Every evening at 7:40, and a few other times during the day, you heard awful noise for a minute or two if the system was set to play the digital server audio. The noise is on standard time though... it happened an hour earlier after we went off summer time.
No nearby interference source was found: no medical offices or tv or radio stations nearby, no taxi stands, no ham antennae visible...
After relocating the d-a nearer the remote sound rack, installing shielded cat6 cabling for the AES lines, replacing the D-A, even replacing the projector and server... we brought an AM radio into the booth. Tuned to a dead frequency, it squawked up a storm at the same time the film audio went crazy.
A spectrum analyzer showed that a nasty periodic HF burst on the AC line was the cause. No explanation as to why it happens on schedule. The power utility is still investigating: the site has a second (apparently clean) power feed and the digital projection system is now running on temporary cable from a panel on that feed - with no noise problem.

Posted by Peter Maddock (Member # 7652) on 02-09-2015, 05:36 PM:

Thanks Dave. For me a lot of ths seems bizarre having got involved with 35mm and now digital projection at a late stage of life and not much experience with audio.
We seemd to have solved the problem after a number of CP750s were supplied to us originally because of a faulty display screen. It appears we may have had a faulty DB25 input socket on a replacement CP750 which was a reworked unit.
We now have a new CP750, albeit one which was reworked because of a quality issue during manufacture. We have not had any more crackling since this CP750 was installed.