PDA

View Full Version : How to lower latency.



tjwuth
12-07-2007, 04:44 PM
We were sold a VT4 (now VT5 with recent upgrade) in July and have had numerous problems with it. We finally got all the bugs worked out (we hope) but the latency is still too much. We measured a 2.75 frame (or about 92ms) delay which is within Newtek's standard, but for live video, it's just way too much. I spoke with a tech from newtek and he said that he had heard of people that were able to tweak their computers enough to get the latency under 1 frame. If you have been able to achieve less than 2 frames, please let me know what you've done. Here are our specs:
Processor: Intel Core 2 6600 @ 2.4 GHz
Motherboard: Gibabyte GA-P35-DQ6
Memory: 2GB Corsair XMS2
HD: 250 GB for System 600 GB Raid 0 for Video drive
Video: nVidia Geforce 8500 GT with 256MB
This is a dedicated VT machine so there is minimal software loaded on it.

Thanks in advance,

ted
12-07-2007, 08:08 PM
Since you're in my neck of the woods, e-mail me and we'll chat.

PIZAZZ
12-08-2007, 08:40 AM
2 frames is the best you can get and that requires Genlocked cameras to achieve 2 frames. The VT requires 1 frame to sync on the way in and 1 frame to sync on the way out. The infamous Trinity/Globecaster had 2 frames. The Grass Valley Indigo HD switcher has 4-5 frames as does the Sony Anycast.

Make sure to turn off any additional processing in your projector and minimize any other gear between the VT and Projectors.

SBowie
12-08-2007, 09:34 AM
I'm curious about the installation layout here. In most decent size venues, delays related to speed of sound from the speakers would be more relevant.As a rule, a 2-3 frame delay isn't problematic beyond the stage and closet rows of seating. Is this a more intimate environment, or are other factors involved?

tjwuth
12-09-2007, 11:06 AM
2 frames is the best you can get and that requires Genlocked cameras to achieve 2 frames. The VT requires 1 frame to sync on the way in and 1 frame to sync on the way out. The infamous Trinity/Globecaster had 2 frames. The Grass Valley Indigo HD switcher has 4-5 frames as does the Sony Anycast.

Make sure to turn off any additional processing in your projector and minimize any other gear between the VT and Projectors.


Then why does the manual say you don't need to Genlock? According to the manual VT syncs internally. I did find it odd that they provided Genlock and then say that you don't need it. Besides, and correct me if I'm wrong, isn't the purpose of Genlock just to sync the horizontal and vertical frequencies so that each input is generating the same line as the other so that when you switch the picture doesn't jump? (I apologize for my ignorance, I'm a Technical Director but audio is my forte)That is one of our other problems though is that we are unfortunately using some Cannon GL2's right now (against my recommendation) which as you know are not genlockable.

What cameras do you like?

mhenstell
12-09-2007, 01:42 PM
The VT system does automatically frame sync non-genlocked cameras, however, using the frame sync feature adds some bit of delay.

tjwuth
12-09-2007, 02:43 PM
I'm curious about the installation layout here. In most decent size venues, delays related to speed of sound from the speakers would be more relevant.As a rule, a 2-3 frame delay isn't problematic beyond the stage and closet rows of seating. Is this a more intimate environment, or are other factors involved?

Our venue is a 1000 seat church auditorium where the farthest seat is about 90 feet from where the pastor stands on stage. We use image magnification for a few reasons like poor sight lines, a CCTV system in other parts of the building and most important is to keep the people towards the back connected with the message. So yes it is a more intimate setting than say an arena. We project the video image onto two side screens that are on each side of the stage. We have a center screen above the stage but we only use it for presentations, graphics and video clips. We also have great audio so it's not like there is enough reverb in the room to cover over some of the delay. 2-3 frames is very noticeable. We have a confidence screen in the back of the room for note and lyrics and I put the camera image on that screen and delayed the audio in the house by 92ms and had the band try to play. They couldn't. We found that with our 92ms delay of video, it was way to distracting especially if there was fast movement from the stage. When someone would wave their arm, you'd catch the delay in your peripheral vision.

nevmoor
12-09-2007, 03:39 PM
Most switchers with internal sync like the MX50 or 70 have the same issues as a VT. For example on an MX 50( or 70 in "A/B mode") there is delay introduced while syncing the next source. As a result these units have a 2 frame delay just like VT. The genlock feature is not really for the VT per say, it is to get all the cameras horizontal and vertical sync to happen at the same time so that the VT (or any switcher) doesn't have to adjust and lock the signals together.
Unfortunately this is the reality of IMAG. I have seen the most expensive set ups and there has always been at least 2 frames of delay. Using an Analog Way or Fulsom ScreenPro has the same result. The simple fact is that these systems have to digitize, process and then pass the signal along to a projector that has to do some processing of its own.
It can be really aggravating especially on uptempo songs, but unfortunately it is a reality.

nevmoor
12-09-2007, 03:43 PM
We use an MX20 for our IMAG switcher, which has separate DA'd feeds. The DAs feed both the IMAG and the VT. I knew that the VT would have too much delay for our size venue. Our church seats about 800 but the furthest seat is about 80 to 90 feet.
There is still a 2-3 frame delay from cam to projector in our set up.

teh_duke
12-11-2007, 05:07 PM
I hate to be a total nube in this discussion, but I have to ask. If the system is genlocked by a black burst generator and all cameras are connected to the generator, then by all means, the frame latency should only be the two frames, right? Now, does that mean if you turn off the frame sync feature in the vt, that it will cut down on processing requirements as well?

Paul Lara
12-11-2007, 05:10 PM
...does that mean if you turn off the frame sync feature in the vt, that it will cut down on processing requirements as well?

It's not possible to 'turn off' the internal frame sync, as incoming streams are stripped of sync and replaced with the new timing.

billmi
12-12-2007, 08:09 AM
Our venue is a 1000 seat church auditorium where the farthest seat is about 90 feet from where the pastor stands on stage.

The furthest seat is 90 feet from the screen. How far is it from the speakers?


, a CCTV system in other parts of the building

I take it your signal is properly synced here, yes?


2-3 frames is very noticeable.

It is unfortunately though, a fact of life in IMAG though such a small delay is usually overlooked in typical places where IMAG is needed because so much of the audience is so far away their focus the screen not the stage. When people are in close enough that the projection is more for impact than mere visibility, the visial difference is easier to spot. Audio delay is a whole other can of worms too, as sound delays itself while passing through the air, so some video delay is usually desirable, if the main audio source is at the front of the venue, in order to improve the A/V synch for folks in the back row.

Any digital video mixer is going to introduce delay. Even if you remove delay from the production side by using an old-school analog mixer (cuts and dissolves/wipes only, no DVEs) and genlocked cameras, you'll still have at least a frame of delay from the scalers in the projectors, unless you can find some old analog SD projectors too.

PIZAZZ
12-12-2007, 08:36 AM
Even if you remove delay from the production side by using an old-school analog mixer (cuts and dissolves/wipes only, no DVEs) and genlocked cameras, you'll still have at least a frame of delay from the scalers in the projectors, unless you can find some old analog SD projectors too.

Many of the large projectors allow you to turn off the processing that adds to latency. I am talking about the large format DLP Barcos, Christies, usually 20K plus projectors. Very few of the sub USD 10k projectors we have come across allow the processing to be turned off. So you are stuck with a frame or two no matter what.



Oh the costs of going digital........ an unfortunate but unavoidable situation.

alexxi
12-13-2007, 12:59 AM
...
The Grass Valley Indigo HD switcher has 4-5 frames as does the Sony Anycast.

...

Pizazz, just a small correction:
Especially because of this delay-Issue for IMAG and permanent discussions with our local broadcaster, we added an Indigo switcher to our pool.
The framedelay for unsynchronized sources is exactly 1 Frame (from In to out regardless of the source). Genlocked Sources between 6 to 12 Lines. Even using Cameras without CCUs as a Syncsource without 100% proper Adjustment, we never get more than 1 Field delay.

VT 3(4) is one of the best concepts of mobile production Im still using, but unfortunately the weakest point is this delay issue for IMAG. In 90% of our setups we run in a 3-4 Delay ... + projectors delay and we are out of the game....

bg
alex

Cineman
12-13-2007, 05:14 PM
We measured a 2.75 frame (or about 92ms) delay which is within Newtek's standard, but for live video, it's just way too much.

The framedelay for unsynchronized sources is exactly 1 Frame (from In to out regardless of the source). Genlocked Sources between 6 to 12 Lines.
Forgive me folks. I really try not to post on threads unless I think that I can contribute something. For just this once, and for my own education, can you please tell me how you are able to determine video delay to less than a field.

Thanks,

Nes Gurley

PIZAZZ
12-13-2007, 05:57 PM
Pizazz, just a small correction:
Especially because of this delay-Issue for IMAG and permanent discussions with our local broadcaster, we added an Indigo switcher to our pool.
The framedelay for unsynchronized sources is exactly 1 Frame (from In to out regardless of the source). Genlocked Sources between 6 to 12 Lines. Even using Cameras without CCUs as a Syncsource without 100% proper Adjustment, we never get more than 1 Field delay.

VT 3(4) is one of the best concepts of mobile production Im still using, but unfortunately the weakest point is this delay issue for IMAG. In 90% of our setups we run in a 3-4 Delay ... + projectors delay and we are out of the game....

bg
alex

Alex,

I am merely repeating what my Grass Valley rep told me. I will need to confirm this information again. There might be some differences when using different inputs. The AnyCast's latency changed depending on what input format you were using maybe the Indigo does too.

****** A Good Feature ********
"The VT5 will stay a consistent 2-3 frames of latency No Matter What input you are using... " There is always an upside. :)

deaddavey
04-03-2008, 08:32 PM
is this noticeable on singing or speaking?

ted
04-03-2008, 09:36 PM
As mentioned before, it won't be a problem as long as you don't have the screen directly behind or next to the speaker/singer.

Of course, "not a problem" is subjective. :) And you can add delay by not setting it up properly.

CreatvGnius
04-03-2008, 10:57 PM
Forgive me folks. I really try not to post on threads unless I think that I can contribute something. For just this once, and for my own education, can you please tell me how you are able to determine video delay to less than a field.

Thanks,

Nes Gurley
Tee-hee!
:beerchug:
My sentiments, exactly! I can't help but wonder if there is perhaps a human, depraved tendency -- to think that digital video, at less than 1/10 of a second is really bothersome at all as well.

But then, curiosity is leading me to suspect that it may be, that some latency that's likely inherent in some source(s) -- such as digital cameras' CCD and CMOS imagers, A/D processing circuits and the like -- let's not even mention image stabilization voodoo -- is encroaching on the scene.

All this -- before an input signal ever hits the digital video mixer employed at the venue (e.g., TriCaster, or VT, or what have they).

Such can be the case, especially if one has some digital processing engaged, via the Menu options -- some forms of electronic "image stabilization" and other image enhancement techniques, let alone the normal function of the image sensors in digital cameras.

Then there's the gross, cumulative effect for added latency (downstream of TriCaster's mere 1/10 of a second or less) -- seen in a digital display (LCD projectors, anyone?) that's got some scaling, line-doubling and/or some other "enhancement" tricks up the sleeve.

Please forgive me, too.
-PeterG

blazer003
04-05-2008, 03:44 PM
2 frames is not noticeable to anyone except those that are trying their hardest to see it (aka you).
3 will still not be noticed by anyone who isn't specifically looking for it, or maybe if there is an imag image directly behind the presenter. But I would still consider this completely acceptable.
4 will still probably not be noticed by your average person, but it may catch someone's eye, especially if there is fast movement and the speaker is in front of the screen (guitar playing directly in front of the screen can sometimes be noticed). Beyond that there are problems.
5 is noticeable by quite a few, and is where IMO it is unacceptable.
6+ is complete no go.

This is just my experience, but it's hard for me to believe that sub 3 frames is too much.

If I could just get mine down to 4 in our auditorium I'd be a happy man.

Jim_C
04-05-2008, 05:17 PM
I think we(us tech/in-house guys) also tend to overestimate our audience's perception and credit them with caring more than they actually do.

;)

>>Overheard convo leaving the Church.....
worshipper #1: "Wow did you HEAR the Pastor's sermon? What a powerful message!!!"
worshipper #2: "Forget the message, did you notice they had less than 2 frames of latency??! Now THAT'S a Miracle!"