bthebassman Posted March 20, 2019 Share Posted March 20, 2019 We’re using a new WXGA over CAT6 video sender (LKV383VGA-POE) from stage to our video mixer (Roland V40HD), and routing the audio from the stage via DI and AR2412 to our GLD80. The video is (shockingly) delayed by about 600mS compared to the audio!!! There are several ways to tackle this…1. Delay the audio to sync up to the video in the GLD2. Send audio and video from the video mixer only (no issues)3. Buy in a dedicated audio delay (I have an Alesis Microverb somewhere?)4. Change the WXGA sender / receiver Option 1:On the Allen and Heath GLD80, I found a built in input channel delay of 100mS – not nearly enough, so then thought I’d use our FX delays for as clean as possible delay. First I tried routing through a group, but for some reason hit a brick wall when trying to send the group to main mix?? (Maybe I’m just having a dumb day?). Anyway, I know how to route the Group through FX to delay as a stereo pair, and I’ll probably solve it tonight as I nod off,(am I in good company here?).So, after being defeated, I then thought, use an insert into each input channel – which works well, BUT – although the FX delay is stereo in/out, the FX channel will only allow 1 insert at a time, so I had to use 2 FX channels, one for Lin and 1 for Rin. Working but not ideal.Option 2 and 3 are practical but not the elegant solution I’m looking for. Option 4 is admitting defeat. So the question is, for around 500-600mS of good, clean, stereo delay, what is best practice? ...or... How can I fix the video delay? Link to comment Share on other sites More sharing options...
Dave m Posted March 20, 2019 Share Posted March 20, 2019 I'd be tempted to send the audio through the vision mixer to retain synch.It's already there. Datavideo used to make an audio delay for the purpose. I presume the delay is due to the mixer and not the CAT6? Link to comment Share on other sites More sharing options...
timsabre Posted March 20, 2019 Share Posted March 20, 2019 I would have thought the delay is mostly in the cat6 video sender. The mixer won't be adding more than 1 or 2 frames delay. The Roland V40HD has a variable audio delay 1-12 frames which might sort you out though, if your application can live with everything being delayed. Link to comment Share on other sites More sharing options...
Brian Posted March 20, 2019 Share Posted March 20, 2019 3. Buy in a dedicated audio delay (I have an Alesis Microverb somewhere?) Keep an eye on eBay for a 'BEL' audio delay. They go for not much money and are often fitted with oodles of delay time. (oddles = >1 second) Link to comment Share on other sites More sharing options...
mackerr Posted March 20, 2019 Share Posted March 20, 2019 I would start by determining where in the signal chain all that delay is coming from. It may be possible to change some settings to reduce it at the source. 600ms is 20 frames of video, that is quite a lot. There is probably at least a frame of delay at each conversion point, and possibly several frames in the video mixer, depending on how the mixer is set. Leaving video effects in the mixer enabled when you are not using them will add delay. In a large hall there will also be acoustic delay based on time of flight. I usually consider being plus or minus 1 frame to be acceptable lip sync, so you have an audience depth of around 20m where you can achieve good sync. beyond that you will have to decide which 20m of audience depth is most important to have as that good sync zone. Mac Link to comment Share on other sites More sharing options...
sandall Posted March 20, 2019 Share Posted March 20, 2019 Good thinking, though It's only 15 frames on this side of the water. Link to comment Share on other sites More sharing options...
GaryNattrass Posted March 21, 2019 Share Posted March 21, 2019 bane of our lives in broadcast now trying to compensate fo the pics being out of sync, they always blame sound tho! 12-19 frames and trying to re-sync Skype too from 5,000 miles away is just a joke! Cheap Cheap Cheap all the time! Link to comment Share on other sites More sharing options...
alistermorton Posted March 21, 2019 Share Posted March 21, 2019 Going slightly off topic, but it always annoys me that on the same channel some programmes are in sync and some are badly out. You'd need to be constantly adjusting delay lines at home to keep just a single channel right. Link to comment Share on other sites More sharing options...
sandall Posted March 21, 2019 Share Posted March 21, 2019 Met an interesting effect when using iPlayer's "Restart programme", when the sound is continuous, but the picture jumps forward every now & again, so ends up several seconds ahead of the sound. Only noticed so far on Mr Portillo's railway journeys. Link to comment Share on other sites More sharing options...
sameness Posted March 23, 2019 Share Posted March 23, 2019 Met an interesting effect when using iPlayer's "Restart programme", when the sound is continuous, but the picture jumps forward every now & again, so ends up several seconds ahead of the sound. Only noticed so far on Mr Portillo's railway journeys. Trains are never on time though... :P Link to comment Share on other sites More sharing options...
mac.calder Posted March 23, 2019 Share Posted March 23, 2019 Extenders should not be giving you that level of delay - HDBaseT and HDBitT should both be near zero latency. Even AV over IP 1GHz solutions are sub-frame latency. It is relatively easy to check if it is the extender - get a laptop or PC with two outputs. Plug in two computer monitors and duplicate the displays. Run a timer app with milliseconds on it and take a video of the two screens. They should pretty much be in sync. Then put the extenders in line. Take another video. Compare. I would then start to add everything else in the video chain in line as well. If you are getting 600ms of delay from the extenders, return them and demand a full refund, because they are not conforming to the HDBitT spec. Link to comment Share on other sites More sharing options...
bthebassman Posted May 8, 2019 Author Share Posted May 8, 2019 Sorry to disappear, but I'm back now. I presume the delay is due to the mixer and not the CAT6?Thanks Dave. It's defo not the mixer or CAT6 - tested negative. It's the Lenkeng TX/RX. I would start by determining where in the signal chain all that delay is coming from. It may be possible to change some settings to reduce it at the source. 600ms is 20 frames of video, that is quite a lot. There is probably at least a frame of delay at each conversion point, and possibly several frames in the video mixer, depending on how the mixer is set. Leaving video effects in the mixer enabled when you are not using them will add delay.The Lenkeng TX/RX was the culprit. We have cheaper (nastier) VGA and HDMI extenders - all those are fine!In a large hall there will also be acoustic delay based on time of flight. I usually consider being plus or minus 1 frame to be acceptable lip sync, so you have an audience depth of around 20m where you can achieve good sync. beyond that you will have to decide which 20m of audience depth is most important to have as that good sync zone.The hall is 12m deep and 20m wide, so very little acoustic delay to worry about. Thanks for the input mackerr. Extenders should not be giving you that level of delay - HDBaseT and HDBitT should both be near zero latency. Even AV over IP 1GHz solutions are sub-frame latency. It is relatively easy to check if it is the extender - get a laptop or PC with two outputs. Plug in two computer monitors and duplicate the displays. Run a timer app with milliseconds on it and take a video of the two screens. They should pretty much be in sync. Then put the extenders in line. Take another video. Compare. I would then start to add everything else in the video chain in line as well. If you are getting 600ms of delay from the extenders, return them and demand a full refund, because they are not conforming to the HDBitT spec. Hmm. Thanks Mac for that. No surprise that, support@lenkeng.com bounces straight back! Time to contact the cc for refund. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.