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Author Topic: Cinema room calibration test tone suggestions Anhtu Vu Film Handler Posts: 98 From: Montreal, Quebec, Canada Registered: Jun 2013 posted 06-11-2015 12:00 AM                     We have 2 cinema room that needs to be calibrated on a regular basis. One is using the CP650/QSC DCM10 and the other, a soon to be installed Qsys core 250i processor. I use the test tone generated within the CP650 but it's a pain to use and i'm questioning its accuracy, are there any test tone generator or files i can ingest directly into the DCP server for this purpose ? thx  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 06-11-2015 05:32 AM                     Which tools do you use for calibration? No big deal to put pink noise and sweeps into a DCP. - Carsten  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 06-11-2015 05:52 AM                     The CP650 pink noise is actually decent and trustworthy. MANY rooms have used it as "the" reference. My only fault with the PN in the CP650 is that it is quieter than previous Dolby processors (e.g CP500 or any that relied on the CAT85 generator) so rooms set with the CP650 WILL be louder than older Dolby processors. In the DCinema world, this is no longer of any consequence though.  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 06-11-2015 06:52 AM                     This is not meant to calibrate a room in a technical sense, but it still fits the thread topic decently, so I'll link to it anyway... http://www.freedcp.net/dcp/test/bewegte_bilder-tricks17-test_film-full_content-51-j2k.zip It's a test-suite for image and sound, it has german, english, french comments, contains full and individual channel noise and sweeps, and some orchestral parts. - Carsten  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 06-11-2015 08:26 AM                     quote: Steve Guttag My only fault with the PN in the CP650 is that it is quieter than previous Dolby processors (e.g CP500 or any that relied on the CAT85 generator) so rooms set with the CP650 WILL be louder than older Dolby processors. Steve - is that a different issue than this one? http://forum.qscservice.com/viewtopic.php?f=3&t=3728#p14604 (bottom post) edit: Looks as if it is: http://www.film-tech.com/cgi-bin/ubb/f1/t010229/p1.html - Carsten  |  IP: Logged Harold Hallikainen Jedi Master Film Handler Posts: 906 From: Denver, CO, USA Registered: Aug 2009 posted 06-11-2015 08:57 AM                        Do the rooms need to be calibrated on a regular basis or checked on a regular basis? I don't see what can drift much in current electronics. Harold  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 06-11-2015 09:34 AM                       More like verify the levels are correct as one never knows who did the job before you.  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 06-11-2015 03:43 PM                     Carsten, No, that is just that a 650 is 'idiot proof' and will reduce the digital gain internally before the DSP so you can push ALL the EQ up and you will not clip the internal DSP. On a USL processor you can select how much dynamic you want, the Dolby is fixed. The AP20 for example does not pad the input and as such the internal dynamic is zero. If you use any positive EQ, the internal DSP *will* clip when it receives a 0dB FS at that frequency. Dirac does not apply as it cuts only. What Steve mentioned was that Dolby have changed the reference level over the years. Hence if you align a room using a CP500 your final levels will still read 85dBC but since the reference level is LOUDER, the film will play softer. To better explain, if you run a Dolby Digital Pink Noise print on a system aligned at 85dB on a CP500, it won't ready 85dBC in the auditorium. I believe it is approx 2dB difference (1.6?) so it should read 83.4dB. Same print, aligned on a CP650 will read 85dBC in the room. I guess Steve says that it does not apply with DCinema anymore because you can now run reference pink noise from the server and align the LEVELS using that. That will take into account the whole chain.  |  IP: Logged Anhtu Vu Film Handler Posts: 98 From: Montreal, Quebec, Canada Registered: Jun 2013 posted 06-11-2015 03:55 PM                     quote: Steve Guttag The CP650 pink noise is actually decent and trustworthy. MANY rooms have used it as "the" reference. My only fault with the PN in the CP650 is that it is quieter than previous Dolby processors Well, this is kind of contradicting as a ''trustworthy'' PN should not vary from one processor the another. Personally, i've never trusted the test tone generated from the CP650, but then again, as a mixer i'm super picky. Anyways, has anyone heard of this ? https://www.sounddogs.com/suppliers/2746.htm  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 06-11-2015 03:56 PM                     Oh well. So much for 'Fader 7'... - Carsten  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 06-11-2015 04:41 PM                     There is nothing wrong with the 650's PN and it's very consistent between... 650's. I believe 750's will have the same level as well. You will find that AP20s and QSC and Dolby all have slighty different pink noise. That is why using a CPL is the final level.  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 06-11-2015 06:47 PM                     Anhtu - you choose your test tones after your tools (or measurement methods). Aside from real music and soundtrack examples, the only test-tones I ever needed were pink noise and sweeps and the occasional sine. You get them everywhere, and even with free tools like Audacity you can create them (and analyse them) to your specific needs. If you 'buy' something, you need to make sure it has the proper digital level. If you're able to verify this, you can create it yourself just as well. A DCP can be a source for 16 channels of 24Bit/96KHz test signals. I don't think you should distrust the CP650 internal generator. Actually you can use it as a reference for other software generated patterns. As one of your rooms does not use a CP650, a DCP is the easiest and most practical thing. - Carsten  |  IP: Logged Anhtu Vu Film Handler Posts: 98 From: Montreal, Quebec, Canada Registered: Jun 2013 posted 06-11-2015 09:47 PM                     I've tested the CP750 before settling for the QSC and, unless there was something wrong with the demo, its PN level was different than the CP650.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 06-12-2015 06:07 AM                     Starting with the CP650, Dolby lowered the internal level of the pink noise generator. as such, you will turn the gains up higher for it to reach 85dBc. This is in comparison to the CAT85 PN generator card (or Component Engineering's SG-1). I'm pretty sure the CP750 has followed suit. Thus a -20db reference signal into a CP650 (or CP750) should be at 85dBC but would be lower in legacy products. So again, what is different is the Pink Noise level in the CP650 and later versus legacy products (of which, now the CP650 is also legacy). Naturally, if you always use your own external generator, you will have consistent results through all processors (like we did in the Dolby analog days). I don't know many people that don't use a processor's internal PN for tuning. When I did a DTS/Dolby/SDDS shootout many moons ago, that is when I discovered that SDDS cheated their outputs by using an HF deficient PN such that you would tend to tune an SDDS a bit "bright." I say it doesn't much matter now since going forward, not too many people are going to put in legacy products (or have some CP65s and some CP650s to have the reference discrepancy show up. I do find it interesting that Dolby dropped the AES level down 10 dB (haven't verified it) on the CAT778. I've used the card an never had a level issue with it. One would think if you are going to design a product like the DCM10D and that the CP650 is a likely candidate, that you would have a CP650 setting that would apply suitable gain to the input stage. Then again, with the CAT778, that is supposed to be used by better than the average person that should understand digital clipping and not tune a room such that the EQ stage is being used as a gain stage too. There shouldn't need to be a pad in there. The CP650 DOES have two choices on gain stages...that is there is "normal" and "noise floor optimization." Which like the JSD series protects you or not from getting into trouble. By going to noise floor optimization, you lower the noise floor by using more of the "bits." for signal. I wonder if on the CAT778 if you went to that mode if you wouldn't get the gain back that was taken away. Also one shouldn't forget on the DCA amplifiers...the Dataport inputs have resistor pads on them such that if you are using the Dataport inputs, you are supposed to raise the inputs to maximum. Due to this, I've seen DCMs clip out before the amplifier. It is one of the things that drove me away from the DCMs and the whole Dataport thing. You are going to have more difference nowadays on how the surrounds are set up.  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 06-12-2015 07:19 AM                     Well, the CP650 has the difference between analog and digital outputs. Then with internal crossovers... The CP750 has only analog outputs. So it's not easy to actually verify the pn level that is generated internally. You have to trust it. Of course you can compare different CPs, but which is right and which is wrong... As with color and brightness shooting, it is always best to have the signal come from a DCP, as it will run through exactly the same signal pipeline as final content. More and more servers offer mix/level functions now, so it get's more important to be able to rule that out as well. It's also quite easy to tap into AES signals between server and processor to get to the ground of things if needed. - Carsten  |  IP: Logged

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