Author Topic: Lip-synching and cable TV delays  (Read 1392 times)

Redlight

  • Enjoying life in the slow lane
Lip-synching and cable TV delays
« on: 26 April, 2017, 03:24:17 pm »
I went along to the recording of Later with Jools Holland last night. It was all good fun - the usual mixed bag of established names and interesting newcomers. And I got to shake Robert Cray's hand at the end, so that made it all worthwhile.

However, I found myself wondering on the night whether one of the acts was miming. (I'll leave you to try and guess which when you see the show on Friday). The vocals were just a bit too perfect and I thought I picked up hints of double-tracking and an instrument that wasn't visible. 

As well as the recording, they put on a half hour live show that went out last night (natch) so I watched it on I-player today to see if I was right.  I'm now convinced that I was, on the sound alone, but I also noticed that all of the other acts' vocals seemed to be slightly out of synch with their lip movements even though I know for sure that they were performing live. 

Does anyone know why that might be - is it a quirk of watching on cable or i-player?  (If so, I may need to take back some of my snarky comments about the 2012 Olympics closing ceremony!  :-[)
Why should anybody steal a watch when they can steal a bicycle?

Kim

  • Timelord
    • Fediverse
Re: Lip-synching and cable TV delays
« Reply #1 on: 26 April, 2017, 03:34:33 pm »
It's really hard to keep video and audio in sync these days.  Pretty much everything that manipulates digital video in some way (all the way from the camera to your TV itself) will introduce a delay, which then has to be matched in the audio path, or it ends up out of sync.

Big live events are particularly hard, because you end up with different video paths on different camera feeds.  A pooled feed might have more delay than your own cameras.  A wireless mobile camera may end up with a few frames more lag than the wired ones.  Where's the audio coming from?  A central mix, or a mic up near the camera for interviews?  What do you set the audio delay to to compensate for that?

Plenty of opportunity for someone to cock it up at most stages in the process, and a general lack of people monitoring the results.  Humans cope with lagged sound reasonably well, as that's what happens in the physical world, but sound leading picture is extremely unnatural and easy to achieve by accident.

At least with a recording, you can take the time to get the AV sync correct in editing.


I expect redshift will be along in a minute (±15ms) with a more informed rant on the subject.

clarion

  • Tyke
Re: Lip-synching and cable TV delays
« Reply #2 on: 26 April, 2017, 03:44:34 pm »
Recording is not my thing, but I hate miming.

My boss was booked to provide a PA for the Village People (give or take a few members), being told to expect radio mics.  He was disgusted when they produced these 'microphones', which were just sawn-off bits of broom handle, and he was handed a badly-edited (as it turns out) reel of tape.

Divine was too pissed even to mime, sadly.  SPK made a big show of beating bits of metal (and gouging a bit out of the wooden floor* when an attempt to crowdsurf with a hatchet in each hand was declined by the crowd nem con), but it was all sham.

I loved Robert Cray.  What a lovely man, and what a talent!  One of the highlights of my time in the biz.

* for completeness, I should add at this point that the tour manager inspected the damage and pronounced that this was not the result of axe-wielding, but of overenthusiastic dancing while wearing stilletos.  His version of events did not prove the most popular, and the band's fee was adjusted.
Getting there...

Kim

  • Timelord
    • Fediverse
Re: Lip-synching and cable TV delays
« Reply #3 on: 26 April, 2017, 03:47:18 pm »
He was disgusted when they produced these 'microphones', which were just sawn-off bits of broom handle

I can't work out whether that's worse than the unplugged SM-58 you see from time to time.  At least someone made the effort to saw up some broom handle...

clarion

  • Tyke
Re: Lip-synching and cable TV delays
« Reply #4 on: 26 April, 2017, 04:28:34 pm »
;D

They did at least have them in a flight case.
Getting there...

redshift

  • High Priestess of wires
    • redshift home
Re: Lip-synching and cable TV delays
« Reply #5 on: 26 April, 2017, 08:07:22 pm »
TV audio timing is a pig even in the studio these days.  A significant portion of my time is taken up trying to re-synchronise audio and video signal after their various (separate) paths are brought back together at the output side of the studio.  We frequently have to do 'clap tests', which are exactly what they sound like - some poor sod has to sit in front of the camera and clap on command while we all huddle round the monitors trying to work out if it was early or late.  Late sound is just about listenable.  Early sound isn't.  The hi-tech version of the clap test is SmartLips.  We get a small smirk by calling it HotLips.  There's not much to laugh at in telly.

Digital audio in TV is embedded into the HD-SDI video signal, and each audio embedder has delays built-in so that the sound can be tweaked appropriately.  If you shoot in progressive/PsF, and I think 'Later' is, you have to alter the delays further, because the pictures take longer to process in the camera.  If you use augmented reality (Mastermind, MOTD), you need different delays in each clean camera feed to match the delays caused by the AR processing of pictures from the same cameras.  In some cases the echo between source and programme sound is so distracting that people switch the sound off. 

Then you have the problem of live monitors on the studio floor.  The audience are watching live sound, but any picture monitors a) come from the downstream side of the studio, which is late, and b) are probably LCDs which have anything up to 10 frames of delay in them due to picture processing.  A good example of this can be seen on HIGNFY,  when they cut to the last wide shot for the credits.  If the slung monitor is in shot, you can see it cut to the wide shot late.

For a music show, there's usually front-of-house sound mix for the floor, and a separate mix in the sound gallery which is recorded with the video.  A show like Jools will record multitrack outputs to Pro-Tools or similar for a music mix after editing.

All of the above is complicated further by the habit of recording 'ISO' feeds of individual cameras, which take a completely different path through the studio. Those recording will also take isolated sound tracks which need to be synchronous, and those embedders will need their own settings.

This doesn't even begin to take into account what happens to it when it's transmitted.

It's TV.  Even when it's live, nothing is real.
L
:)
Windcheetah No. 176
The all-round entertainer gets quite arsey,
They won't translate his lame shit into Farsi
Somehow to let it go would be more classy…

Andrij

  • Андрій
  • Ερασιτεχνικός μισάνθρωπος
Re: Lip-synching and cable TV delays
« Reply #6 on: 27 April, 2017, 08:39:52 am »
Fascinating.  Thanks!
;D  Andrij.  I pronounce you Complete and Utter GIT   :thumbsup: