SDI distribution latency

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Jim Switzer

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SDI distribution latency

PostMon Mar 20, 2017 11:11 pm

Hi all. Was looking for help on this topic.
I am the tech at a local church and we have a Roland VR50HD video mixer streaming and recording into a pc at 720p. We also have a monitoring TV in the lobby of the church but it has a serious audio / video delay. It is driving everyone in the church nuts because we can hear the sermon live just on the other side of the door, but the foyer TV is literally 1/2 a second late. If anyone turns the volume up on the TV, an incredible echo results. The delay can be for a number of reasons, most notably because the previous tech modulated the digital signal to analog CATV channel 2 for distribution to the lobby. I will be 86ing the mod.

My question relates to latency when using the mini SDI distribution converters, as well as the mini SDI to HDMI converter. If I take the SDI signal out of the mixer and distribute to all monitors through the BlackMagic SDI distribution converter (as well as the SDI to HDMI converter as a few TV's don't have SDI inputs), will I be faced with any significant delay? The specs don't say too much.

Also, for the TV's that don't have an SDI input, can I split the individual SDI lines to component video for those TV that don't have and SDI input? The TV's we have in the church are not the newest and the budget isn't there to replace all the monitors.

We also have a digital audio board and my other thought was to take the videl and audio separately from each to distribute, right at the source of each before any delays could occur from mixing. I'd have a digital signal directly out of the camera (not sure if it has an SDI output) and take audio from the board then combine (somehow) for distribution. To me that seems most logical because both sources would be before mixing. Is that a crazy thought? If not, how would it be achieved?

Any help with this seemingly silly problem would help. I should also mention that I am willing to replace or run new distribution cabling.... that's a non-issue AFAIC.
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Aaron Rebbeck

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Re: SDI distribution latency

PostTue Mar 21, 2017 8:11 am

A couple of notes for you

Adding non scaling converters and a sdi da wont give you any more than one frame delay if anything.

The tv is often a place where there is alot of delay (just walk around a tv store all with the same scource. they all have diffrent delay.)

Taking a seperate feed off your digital audio desk that has varible delay will help matching up the audio

Sounds like alot of your delay is comming from modulation

Alot of BM converters have audio embeding which will help if you need to bypass the roland and want to distribute via sdi

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Re: SDI distribution latency

PostTue Mar 21, 2017 8:54 am

I'd be very surprised if any of your TVs have SDI inputs. Not everything which has a BNC connector is SDI.

Domestic TVs often have a lot of processing on their HDMI inputs too. This can sometimes be reduced by selecting the "Game" picture mode.

I'd certainly suggest that running SDI to the TVs and then converting to HDMI is the way to go.

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Re: SDI distribution latency

PostTue Mar 21, 2017 11:18 am

Also the scalers inside of older flatscreen tv's are much more slower..

I had a 7 year old plasma on set this weekend from the customer which gave so much audio / video difference.. That i took out the VA to check what was wrond with sdi signal.. To find out that the plasma itself caused so much processing delay that audio / video sync was completely lost..
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