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Author Topic: CP650 low digital input Leonid Dragilev Film Handler Posts: 8 From: Moscow / Russia Registered: Dec 2007 posted 03-20-2014 02:14 PM                        Hi i have a CP650 with cat790 installed. We used it in external 6 chanels analog mode. recently i tried to switch to digital. I got an AD convertor and AES transformers. But when i send -20 dB signal to AD i get about 12 db level drop comparing to analog chain. AD shows -20 and analog is aligned as well. Any help will be greatly appreciated!  |  IP: Logged Pete Naples Phenomenal Film Handler Posts: 1565 From: Dunfermline, Scotland Registered: Feb 2001 posted 03-24-2014 04:26 PM                     What make/model is the D/A convertor? Check the wiring, if it's not a Dolby DMA8/DMA8+ it may not be pin to pin. Also check the -V arrangement  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 03-24-2014 06:24 PM                        Could he be using a mag input? If so, there is a reversible header that affects gain.  |  IP: Logged Leonid Dragilev Film Handler Posts: 8 From: Moscow / Russia Registered: Dec 2007 posted 03-25-2014 01:07 AM                        I am using 3rd party AD converter with AES to AES-id adaptor wired to option card connector. What is V arrangement? The same setup works flawlessly at another room..  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 03-25-2014 03:45 AM                     If you don't mention the brand/model of the adaptor we cannot help you! Shouldn't a cat 790 be able to accept AES without external converters?  |  IP: Logged Dave Macaulay Film God Posts: 2321 From: Toronto, Canada Registered: Apr 2001 posted 03-26-2014 06:35 PM                     What he says he's doing is using a A-D converter to convert an analog audio signal to AES, then using the CAT790 to input the AES data. One would tend to ask why. Anyway, I think any level change is due to a difference in defining the reference level between the Dolby and the A-D converter. The CP650 format 11 analog inputs don't have gain controls (don't think so, anyway) so they have a set reference level (it's in the Dolby manual somewhere) so a known input signal level will give a known SPL in a correctly aligned cinema at fader 7. Someone - AES? EBU? Dolby? DCI? - has defined the 0dB level for the digital audio. I believe that 100% modulation of an AES/SPDIF signal shows as +20 on the Dolby CP650 level bar display. I haven't seen anything go over +20 from digital input, anyway - and a test tone CPL I have, supposedly recorded at 100%, shows as +20 on a 650 w/790. My experience with A-D converters is that the 0dB reference varies. To avoid clipping, various reference levels are used with various amounts of headroom above "0dB". I think the issue is that your A-D converter's -20dB corresponds with Dolby's -32dB. Just convert 12dB hotter?  |  IP: Logged Leonid Dragilev Film Handler Posts: 8 From: Moscow / Russia Registered: Dec 2007 posted 03-27-2014 01:34 AM                        Dave,you are 100% right! i aligned AD with sine wave and got exactly the result you were writing about. thank you for the help!  |  IP: Logged Pete Naples Phenomenal Film Handler Posts: 1565 From: Dunfermline, Scotland Registered: Feb 2001 posted 03-27-2014 02:54 AM                     Leonid, apologies, I did read your post the way you wrote it and assumed it was a typo. You're converting analogue to AES, to put into a CP650. Why not just use the CP650 6 channel analogue input? I think I would invent some switching/patching if I had multiple sources before I went to the trouble and expense of conversion to AES.  |  IP: Logged Leonid Dragilev Film Handler Posts: 8 From: Moscow / Russia Registered: Dec 2007 posted 03-27-2014 03:14 AM                        Pete, I did it because I need 7.1 at first place and because of noticeable 50hz hum of analog inputs due to unbalanced nature of CP650 inputs. We are using device at mixing stage .  |  IP: Logged Pete Naples Phenomenal Film Handler Posts: 1565 From: Dunfermline, Scotland Registered: Feb 2001 posted 03-27-2014 06:23 AM                     OK now that makes sense to me.  |  IP: Logged Manny Knowles "What are these things and WHY are they BLUE???" Posts: 4247 From: Bloomington, IN, USA Registered: Feb 2002 posted 03-27-2014 02:08 PM                     Does your CP650 show the letter "N" or "U" in the top-right corner of the front-panel display? I understand that you're using the Cat 790 card but the Cat 778 Digital I/O Option card may be similar. The 778 offers two settings for Headroom Configuration: N = Noise Floor Optimization U = Unity Gain Never mind -- just read the 790 manual -- looks like this won't help you. But I will leave this here anyway -- some future user can stumble onto it.  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 03-29-2014 10:19 AM                     Where does the analogue signal come from in the first place? Any D-Cinema server will output AES, why not feeding it straight into the Cat 790??  |  IP: Logged Leonid Dragilev Film Handler Posts: 8 From: Moscow / Russia Registered: Dec 2007 posted 03-29-2014 12:24 PM                        We cannot feed cp650 from a server because we are mixing studio and do not own one. Analog signal comes from console, then balanced to unbalanced active adapter. Anyway we are fine now so thanks everyone  |  IP: Logged

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