Film-Tech Forum ARCHIVE: CP750 with BSL and BSR / 5.1 question

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Posted by Jeff Fruchey (Member # 10302) on 06-10-2018, 03:28 AM:

Greetings…Getting ready to install HV/VI-N in both our theatres (*note did order from Odyssey products the 16RJ-7.1-DSSY) but thought I would check to make sure are 7.1 setup is truly playing 7.1 after doing a lot of reading in the forums. We have two GDC SX-2000AR servers and have two Dolby CP750 processors. The GDC servers are running the latest updates from GDC. Our Dolby CP750’s is at version 1.2.8.3 and using the latest Dolby CP750 Setup Software version 1.3.3.0 (64bit) Also using CM-8E Booth Monitors (also updated with latest versions) to which the Dolby CP750 is connected to via the main DB-25F.

Currently within the Dolby Setup our “Main Output Configuration” is set to Dolby Surround 7.1 Output Configuration. (BSL and BSR Installed) We do have separate amplifiers and speakers mounted in the rear for BSL and BSR. We also use Christie Act automation and do use cues for 5.1 and 7.1.

Tested the theatres with the SMPTE_TST Bv21 7.1 and everything was perfect. My question is what happens when playing 5.1 content in the Decode Mode 5.1 Discrete to the BSL and BSR channels? When I ran the SMPTE_TST Bv21 5.1 (Decode Mode is also now set to 5.1 Discrete) the BSL speakers now seem to carry the same information as the LS and the BSR speakers seem to carry the same information as the LS. Is this normal?

Thank you in advance for any information.

Posted by Carsten Kurz (Member # 5396) on 06-10-2018, 05:54 AM:

You mean BSL=LS, and BSR=RS? Yes, that is normal when playing 5.1 over properly configured 7.1 systems. Each surround channel gain is reduced by 3dB to achieve the same overall surround SPL as in 'native' 5.1 systems.

If both SMPTE5.1 and SMPTE7.1 play the proper channel indicators through the respective speakers, you're fine.

Note that strictly speaking, LS and RS are for 5.1 only. In 7.1 systems, they are Left Side Surround/Right Side Surround.

- Carsten

Posted by Jeff Fruchey (Member # 10302) on 06-10-2018, 11:53 AM:

Carsten,

Thank you for the information and the clarification of 5.1 and 7.1. Tonight, we will start installing the HI/VI-N.

Take Care,
Jeff

Posted by Stephan Shelley (Member # 8587) on 06-13-2018, 05:02 PM:

Note with a CP750 set to 7.1 you can connect AES pair 7/8 to the digital 2 input and then you will get an analog signal of the DCP HI and VI tracks on the aux outputs of the 750. There is a circle to check in the general setup to enable this.

Posted by Jeff Fruchey (Member # 10302) on 06-13-2018, 11:38 PM:

That was the configuration I used, and everything is working flawless. To break out AES pair 7/8 I used an Odyssey 16RJ-7.1-DSDY converter board which made life easy. Also took the HI and VI tracks from the aux outputs of the CP750 into the HI/VI-N Terminal Block of the CM-8E Booth Monitor so we can monitor both tracks in the booth.

Posted by Steve Guttag (Member # 268) on 06-14-2018, 07:14 AM:

I'd recommend moving that RCA connector from "AUX 7" to "HI" but leave the VI connected to AUX 8.

Posted by Stephan Shelley (Member # 8587) on 06-14-2018, 02:02 PM:

I second what Steve says. That way you will always have HI. The Aux outputs are DCP dependent and I have seen some independent films have VI and CC but no HI track on the DCP. Also you will have at least HI from alternate content sources using the HI connector on the 750.

You will likely find that the output on the HI connector is lower than the Aux 7. You will need to adjust the input sensitivity of your HI device.

Posted by Jeff Fruchey (Member # 10302) on 06-15-2018, 04:20 AM:

All the main film titles (but not all trailers) we play seem to have the HI track on the DCP but did a little testing per your suggestion and moved the “AUX 7” to “HI,” adjusted the sensitivity on the IRC-28C and played some content. My results seem to be that the “AUX 7” (HI track from DCP) seems to be higher quality audio then the center-weighted sum of L-C-R from the “HI” output from the CP750. Is this a case of hear it all or hear it better?

On another note with Closed Caption Configuration, when I first logged into the USL DCS configuration page the Timeline Offset was set to 1. It was my understanding that positive values make the captions earlier. Should this be set to zero?

Posted by Harold Hallikainen (Member # 5405) on 06-15-2018, 11:18 AM:

The channel 7 HI track is probably better quality than the LCR mix since it may be purposefully mixed for HI. The studios MAY be doing a special mix or may just be doing an LCR mix and compressing it.

On the IRC-28C, the configuration memory is initially erased, so it has 0xff in all locations. In two's complement form, this is -1. This results the timeline offset on shipping units being -1 frame. This is probably close enough for no one to notice, but it would probably be good to change this to 0.

Harold

Posted by Pete Naples (Member # 761) on 06-15-2018, 12:17 PM:

We also connect to the HI output, as Channel 7 is often missing on DCPs here.

Also using HI means it works in alternative content etc too.

Posted by Jeff Fruchey (Member # 10302) on 06-16-2018, 11:46 PM:

Harold, changed the Timeline Offset to 0, tested and seems to be working well.

Pete, when you refer to missing HI on DCPs in Scotland, are talking about main stream feature films not having this or independent films?

-Jeff

Posted by Pete Naples (Member # 761) on 06-17-2018, 05:24 PM:

All of the above Jeff