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Author Topic: DMA8Plus Sound popping issues Pete Naples Phenomenal Film Handler Posts: 1565 From: Dunfermline, Scotland Registered: Feb 2001 posted 09-01-2013 03:36 PM                     is this Ethernet cable shielded? (metal connector shells)  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 09-01-2013 04:40 PM                     I don't think any AES cable/shield issues would cause this: quote: Peter Clay I have noticed when you turn the lights on or off the lights on the DMA8Plus processor go out for a second No matter what quality the cable is, the signal is still symmetrical/balanced. - Carsten  |  IP: Logged Ian Freer Expert Film Handler Posts: 135 From: Wellington, New Zealand Registered: Oct 2003 posted 09-03-2013 05:58 AM                     I have recently noticed similar issues in a couple of new installations. Servers in both cases are GDC SX-2000AR. Both have Dolby DMA8+ adaptors. One projector is NEC NC-2000, the other is NEC NC-3240 I thought it may just be a weird incompatibility between the GDC's and the Dolbys, but if the original poster here has the Doremi/NEC IMS unit then that rules out the GDC... Unfortunately, plugging the DMA8+ into a UPS does not resolve the issue (for me at least). I have a current support query open with Dolby, but have not had a chance to get to site recently to check on things. In both cases I am using the 10m Shielded Cat6 supplied by GDC. It is probably unrelated, but both cases are film festival venues where we have kept reel-to-reel 35mm installed for archival requirements. One site is a CP65/DA20, the other a CP650. Dolby have suggested trying a shorter Ethernet cable and also checking for high impedance of the earthing between the audio rack, server and projector. In one venue the projectionist noticed what was happening and worked out if they leave the lights etc in the booth alone, it is fine. In the other venue, it seemed to be also be caused by actions outside of the projection room, so it was essentially un-controllable as it is a large theatre with many staff, so we've pulled the DMA8+ for now until we get to the cause of the issue. Once I have had a chance to get back to one of the sites to check the earth impedance, and maybe make myself a long audio cable so I can try a shorter ETH cable, I'll report back, but that will be a week or two away yet. Cheers, Ian  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 09-03-2013 06:49 AM                     For yucks...I'd try a real AES cable in one site to prove/disprove the cable theory. CAT cable is "compatible" with AES though the impedance is in the lower part of the approved range. Proper 110-Ohm cable will rule that out.  |  IP: Logged Pete Naples Phenomenal Film Handler Posts: 1565 From: Dunfermline, Scotland Registered: Feb 2001 posted 09-05-2013 11:17 AM                     That's exactly what I was getting at. I've had a similar problem, site was getting drop outs every time a light switch was thrown, film tower switched etc. The cable in use was the very common green stuff from Canford, which whilst being 100ohm twisted pair, has an overall screen. I switched to a 'proper' AES cable, 110ohm twisted pairs individually screened. End of problem.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 09-05-2013 11:35 AM                     Odds are, this is indicative of another issue (grounding) and the proper AES cable covered it up. With proper AES cable, one has screens over each pair and an overall...plus the impedance is going to be spot on for maximum signal transfer.  |  IP: Logged Harold Hallikainen Jedi Master Film Handler Posts: 906 From: Denver, CO, USA Registered: Aug 2009 posted 09-05-2013 12:12 PM                        I am surprised people have as much trouble as appears to be the case with cables. I believe the characteristic impedance of the cable has to match the terminating impedance, 110 ohms for AES/EBU and Ethernet, to prevent reflections, which distort the signal waveform. Shields prevent electrostatic coupling of signals into the cable (capacitive coupling) but do not prevent I ductive coupling due to magnetic fields. In either case, the coupled signal is coupled equally into the two conductors of the twisted pair. The transformers at each end of the cable SHOULD reject this common mode signal. Shields can introduce ground loop problems. I like using cat5 cable for AES/EBU, but you need to do what you need to do! Harold  |  IP: Logged Pete Naples Phenomenal Film Handler Posts: 1565 From: Dunfermline, Scotland Registered: Feb 2001 posted 09-05-2013 02:23 PM                     In all of the hundreds of screens I've installed, that was the only time I've ever had such an issue. The place was really rather badly wired, so it wasn't really a great surprise. Steve I'm sure you're right about the grounding, but I wasn't about to waste time finding wiring issues for the owners to simply refuse to do anything about it. I'm merely making the point that in the OP's venue, it's worth trying.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 09-06-2013 01:12 AM                     CAT 5 (or 6) is not 110-Ohm cable...it is in the 100 and under range. We have taken another approach too...when we use CAT cable, we often use skew free. The type we use also has an impedance in the right AES range, all cables are the same length so there shouldn't be any timing issues between the channel pairs...and the cable color (Maroon), is unique enough that it is quickly spotted compared to any other CAT cables in the system. Thus far, NONE have given any issue. That said, I'll still use proper AES cable for more critical installations or where the CAT cable could be nestled in with noise. Proper AES cable has NEVER failed me either.  |  IP: Logged Peter Clay Film Handler Posts: 16 From: Alderney, Channel Islands Registered: Aug 2013 posted 09-07-2013 09:16 AM                     Hi thanks for all the info. The guy that installed it is going to send us over another cable to try out so hopefully we should start to get things sorted. Luckilly we normally only do two showings of each film a week during the summer months and now we are moving into winter so we only do the two showings every two or three weeks. For instance we showed "Song for Marion" on Thursday and again this Monday, then the next film we will have is "The Wolverine" on Thurs 26th Sep and Mon 30th Sep. So at least the projector isn't getting hammered all the time. Pete  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 09-07-2013 10:29 AM                     Can you tell us which indicator lights on the DMA8+ go off when switching booth lights? - Carsten  |  IP: Logged Peter Clay Film Handler Posts: 16 From: Alderney, Channel Islands Registered: Aug 2013 posted 09-07-2013 12:02 PM                     Hi Carsten, The lights that go out are the "PCM" and the "Discrete" lights. All the other lights seem to stay on it's just those two. Pete  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 09-07-2013 12:28 PM                     I won't step away from the UPS suggestion for your location, but in that case the popping might indeed be solved by improved AES cabling and/or cable routing. Try to get ethernet cable with individual shielded pairs and proper braided common shield. These are not expensive, you could buy two and cut one to see what's actually in there. S/FTP or SF/FTP. CAT6 or CAT7 patch cables should have these shielding features. As suggested, leaving the ethernet cables cables as early as possible in favor of proper AES cables would be an option. Although in your location a proper DB25 4*AES cable is probably not easy to source. The CAT5->AES converter itself is unshielded/plastic to my knowledge, that could be improved as well I guess. Using a shorter cable and placing the DMA8+ closer to the IMB could be a temporary test to see wether it improves the situation. Seems the problem with the booth light switching can easily be reproduced for testing. Or, get a replacement cable for one of the existing CAT cable, cut the previous in two halves, unwrap the screen and check if there is any shielding at all. - Carsten  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 09-07-2013 01:54 PM                     I'm with Carsten. Replace the cable is a cheap and quick operation you can try before buying an UPS - which is always recommended anyway.  |  IP: Logged

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