Time lag from HD-SDI

G

Godfrey Kirby

Member
We have just been working with an AF101, sending the HD-SDI signal to an Analogue Way 'Pulse' switcher. There was a considerable delay in the video image, post switcher, which would cause problems with audio sync at a 'live event'. (Audio being sent directly to the P.A. mixer) We put up a Sony PDW 350 to check if there was the same problem. The delay, while still being present, was much shorter and could be dealt with by a slight delay being added to the audio.
I know that the AF100/1 is not a 'live event' kind of camera but it does also mean that if you are using the HD-SDI output to an external monitor, for focus pulls and/or operating, everything is going to be a bit late.
Any ideas anyone?

Regards - G.K.
 
FWIW I was at a live event shoot a while back, using several hundred feet of analog cable (composite out). No delay issues. The same was noted with SDI, but due to some issues with switching gear and differences in the six cams used (4/6 didn't have SDI), the producer went with analog.
 
Yes... The HDSDI feed from the AF100 lags. We use it in a live switching environment and it has at times caused issues. It's a 3-4 frame delay (at 60fps). Basically the image processing is NOT 100% realtime and introduces a touch of lag. We offset our audio by approx 3 frames when rendering to compensate.
 
Thanks for feedback - in our quick test, the digital image was a marked improvement over the analogue and given the new(ish) generation of HD digital projectors it's a pity we are back with 'Sync' problems........ I suppose it's a case of finding a camera which is quicker off the mark. It's tricky when the 'Very Important CEO' is hearing himself as a ghostly echo... echo..
 
Godfrey Kirby said:
Thanks for feedback - in our quick test, the digital image was a marked improvement over the analogue and given the new(ish) generation of HD digital projectors it's a pity we are back with 'Sync' problems........ I suppose it's a case of finding a camera which is quicker off the mark. It's tricky when the 'Very Important CEO' is hearing himself as a ghostly echo... echo..
Click to expand...
We found that in a Image Magnification environment, it wasn't that distracting. 3 frame delay out of 720/60fps is tolerable. This is assuming that the ONLY delay you have is from the camera, and none from the switching/projection side of stuff. We find that the issues we have with sync can come in the recorded feed.

Also, when you say "hearing", I assume you mean seeing, right? Or is it an issue of putting the audio into the cam first, and then through SDI out to the sound board? If that's your problem, switch the cabling around and go from mic straight to the sound board, and then send a feed back into the AF100. You won't get delay problems on the AF100's internal recording. That will be in sync.
 
Hi Rev. - We send the video feed to the projector/plasmas so that the speaker can be seen on the screen(s) built into the set. The speakers mic (radio mic or lecturn) goes, as you say, directly to the PA mixer (board). The lag shows up in that audio precedes the video, so we delay the audio. Now the speaker is hearing him/herself just a disconcerting beat after they have spoken. The audio feed from the mixer back to the camera does not have any delay put in and so is recorded correctly, in sync. We try to place the delayed speakers so that they are 'backed off' as much as possible to the person speaking and also give them a small amount of undelayed fold back to drown out the delay.
The HS-SDI image is a worthwhile improvement but leads to a lot of audio 'faffing' - now, if we could get the video to precede the presenter speaking........ Sorry - just a thought......
 
Godfrey Kirby said:
Hi Rev. - We send the video feed to the projector/plasmas so that the speaker can be seen on the screen(s) built into the set. The speakers mic (radio mic or lecturn) goes, as you say, directly to the PA mixer (board). The lag shows up in that audio precedes the video, so we delay the audio. Now the speaker is hearing him/herself just a disconcerting beat after they have spoken. The audio feed from the mixer back to the camera does not have any delay put in and so is recorded correctly, in sync. We try to place the delayed speakers so that they are 'backed off' as much as possible to the person speaking and also give them a small amount of undelayed fold back to drown out the delay.
The HS-SDI image is a worthwhile improvement but leads to a lot of audio 'faffing' - now, if we could get the video to precede the presenter speaking........ Sorry - just a thought......
Click to expand...
Are you sure you aren't getting any lag from the LCD/Plasma/projectors or the conversion to HDMI or whatever? That can sometimes be the culprit. We use AJA Hi5 and don't seem to get lag. Also, the delay off the video should be fairly small, and I would guess that not delaying the audio to match the screens would be better than doing what you are doing. I mean, the only way you should really notice the screens' video delay would be like clapping or something with fast movement. 3frame delay out of 60fps is REALLY minute.

Also, what camera setting are you using? 720p60? Or 1080i? If 1080i, when sending to projectors/plasmas they will be deinterlacing which will cause more delay than if you send 720p60.
 
Hi I have a similar Problem

Setup is a Group of 4-5 are discussing on a stage. Above them is a whitewall where a Picture of them is projected.
Video is provided by myself - Setup is SONY FS7 with SDI-OUT - 50m SDI cable - blackmagic SDI2HDMI converter - HDMI to beamer (beamer provided by Location).
Audio is provided by Location (most likely wireless).

My first test have shown me a slight delay between real Audio (No Transmission) and the Image over SDI,HDMI.. ist about 3 Frames which I consider a good value anyway.
Audio test were not yet done but I want to avoid being there and having nothing in my Hands to synchronize both of them.

My questions:
- Is there something wrong in my Video Setup (I think the delay is mainly from blackmagic and beamer itself) or is this delay typical and physics (which I asume)
- How can the Audio be delayed (what Tools, products can be inserted between the wireless Receiver and the loudspeakers to delay - an how can this be adjusted?)
- Given that the Audio Setup there is really weird and has a GREATER delay than the Video - is there a way to delay the Video?
- Is it typical for Speakers to hear an echo (as we are delaying the Audio) or is this too annoying?

MAny thanks for your help
 
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