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House Reference Questions

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Piers McDonald
House Reference Questions
on Oct 26, 2009 at 5:57:25 am

So the facility where I do most of my work does a mix of SD and HD, there's a GEN10 sync generator used for reference.
But I'm not sure it's being used correctly, and I have several questions.
Currently the GEN10 sends 1080i50 sync to HDCAM and PAL sync to Digibeta.
When playing out to tape, the reference to the edit suites is manually patched between 1080i50 and PAL depending on what format is being played out.
The vast majority of stuff done is PAL and 1080i50, some 720p50 and very occasionally 1080i59.94.

Should we just be using PAL sync to sync all devices, despite also doing HD?
Can an HD signal be synced to SD reference?
If so, is there any point to tri phase HD sync if you're not doing 23.98?
Can dubs be done between HDCAM and Digibeta using HD sync on HDCAM and PAL sync on Digibeta, or should both be syncing to PAL?
How can the HD sync signal be distributed, can a standard def distribution amplifier be used?

Thanks Bob in advance for your informative and humorous response...


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maurice jansen
Re: House Reference Questions
on Oct 26, 2009 at 8:24:54 pm

hi piers

there is a simple relation between the line frequentie of
1080@25i and 625@25i.(i don't have my papers with me so i will give this tommorow if i dont forget ;-0) so a good SPG should be able to crosslock in the vertical domain.
So the first HDline starts at the same time as the first SDline. Hlock is not possible since the line time of a HD line is different to the line time of a SDline.but still can have a relation ?!?!?!
for 720P i have to look.
again i will comeback with you later.
locking to BB to dub from HDCAM to DIGI should not give any problems.

about the distrubution
a good quality VDA like the CDV07 of AXON for instance can distrubute Tri-levelsync.

greet
Maurice



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maurice jansen
Re: House Reference Questions
on Oct 26, 2009 at 9:01:45 pm

oh and what i also forgot to say.
your way of working is OK yes it maybe will work with only BB.
but you are used to do it this way which is completly good.
if it works don't fix it ;-)

greet
Maurice



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Bob Zelin
Re: House Reference Questions
on Oct 27, 2009 at 2:15:09 am

Hi Piers,
Maurice already answered you accurately (I think Maurice and I will start a consulting firm), but here are my silly answers -


Should we just be using PAL sync to sync all devices, despite also doing HD?

REPLY - what I have been doing is bringing up (for the first time in my career) the reference inputs of the VTR's and edit systems to a video patch bay. I take a tri level out of the GEN 10 and send it into video DA, and NTSC (or PAL) black into another DA, and "normal" it to your VTR's, and then patch tri level sync as you need it. I ALWAYS use NTSC (or PAL) sync for HD VTR's unless I am doing 23.98, but you certainly can set the GEN10 for 1080i50, and keep this hooked up to your HD VTR's if you want (via a DA).



Can an HD signal be synced to SD reference?

REPLY - YES !

If so, is there any point to tri phase HD sync if you're not doing 23.98?

REPLY - you will get many opinions on this, but I do NOT use tri level sync for 1080i 29.97, or 720p 59.94. When I occationally get "into trouble", then I switch to tri level sync, but 99% of the time, I just use SD reference. of course for 23.98, you have no choice.


Can dubs be done between HDCAM and Digibeta using HD sync on HDCAM and PAL sync on Digibeta, or should both be syncing to PAL?

REPLY - this is the perfect example of keeping SD sync on both a Sony HD Cam and Digi Beta VTR, and NOT using 1080i50 reference on the HD Cam.


How can the HD sync signal be distributed, can a standard def distribution amplifier be used?

REPLY - yes, a cheapo video DA works - I currenly recommend the cheap Kramer Electronics VM80V (a cheap 1x8 video DA) as a great inexpensive distribution source for both NTSC (PAL) black and tri level sync.

Bob Zelin






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Piers McDonald
Re: House Reference Questions
on Oct 27, 2009 at 4:49:37 am

Thankyou to you both Maurice and Bob!

I kind of thought I knew what I was doing ref wise and you guys have helped me fill in the blanks.
I'm going to sync everything up to PAL SD ref and just use the 1080i50 ref for special occasions when things are acting funky.
Now I don't feel foolish for sticking HD and SD ref ports on the patch panel.

And Bob, you didn't even berate me for using an HD sync generator and not fully understanding how it works! You must be having a good day.

Thanks again guys.


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maurice jansen
Re: House Reference Questions
on Oct 27, 2009 at 8:09:47 pm

hi as promised some background info.

the relation between the line's in 1080i@25Fps vs 625i@25Fps
is a ratio of 9:5. So every 9th line the rising edge of a trilevelsync will coincide with the falling edge of the SD bilevel sync.
This gives a vertical relation that line 1 of a HDfield 1 will coincide with the first line of a SD field every 625fields.

for 720P@50Fps this relationship with SD is a ratio of 12:5 i never calculated the vertical relation ship. but i'm sure there will be a relation ;-)
that's a thing for a rainy sunday afternoon instead of sudoko ;-).

if bob say's a cheapo kramer VDA will do the job i believe him. It is just that VDA's often play a double role in our installation giving me the need for high quality DA's. Even an old archive tape has to be treated with respect and these will often be CVBS and DA'ted with the same VDA. all though i never had problems please be aware of clamping CVBS DA's if they clamp on the frontporch they maybe can give problems with tri-level.

greet
Maurice



People saying they don't make mistake's often make nothing at all!


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Bob Zelin
Re: House Reference Questions
on Oct 28, 2009 at 4:37:03 am

although I use AJA GEN10 on almost every installation these days, the "classis" installation for both tri level and standard black reference is the Evertz 7750 tri level sync card that will also output standard reference. This goes into a 3 slot frame, and is used with Evertz 7700ADA7 video DA's (CVBS) for distribution.
The frame is the Evertz 7701FR, which holds 3 cards (2 DA's and one tri level sync card).

This is the chassis that "started it all".

Bob Zelin




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