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New Mic causes desynchronized audio/video?
Old 1 week ago
  #1
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Thread Starter
New Mic causes desynchronized audio/video?

I offered to help out a local company that does monthly live videos. They're good people I give business to regularly, and it became apparent that they had no clue how to do audio, which is cool, they're doing, they're learning, and in this case, a few sound (no pun intended) principles of engineering could go a long way. I spent maybe an hour getting the rundown of the setup, noticing the many easy fixes I expected, then the following took place.

They mention they tried lavs for one session and it was disastrous. I nod, and said, yeah, omni lavs in a very small, very live space like this could pick up a lot of room noise. They say no, the audio was great. Ok, what's the problem? They had synchronization issues when it came time to edit the video.

Now, video is not my jam. I deal solely with audio, and figured as long as I can interface with the camera ,XLR, mini-jacks, +10, -4, etc. it's all good from there. But they're worried about anything but the camera mounted shotgun mic (Which plugs in to the XLRs on the camera body) causing desync between audio and video. But I can fathom NO reason for a change of mics to be an issue (for good or ill) when it comes to the A/V syncing.

I'm thinking this is most likely a correlation/causation fallacy. We changed A and B went bad, therefore A caused B. Lav's caused desync.

My figuring is that:
A: They just got lucky in the past, and not so lucky on the last recording.
B: Something "broke" between shoots.

Or more likely,
C: Someone/something inadvertently messed with a setting on the camera.
D: Someone/something inadvertently messed with settings or intake in their edditing program.

But, is it possible, in my ignorance of video, that I am missing some strange mic that sends and receives time-code over XLR along with the audio signal. Is there some other bit of esoterica which can cause a mic or line level source to affect the A/V synchronization? It seems unlikely, even insane to me, but I've been wrong before...
Old 1 week ago
  #2
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huub's Avatar
You are right
It is completely 100% impossible.
Unless maybe using very crappy cheap digital over wifi wireless lavs.
Old 1 week ago
  #3
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I think we/you'll need more info about the connection setup to develop a theory about what went wrong.

Was the lavalier audio ahead or behind the video timing? That's a big clue as to whether it's an in-camera or software/import problem. Also getting an idea of how much time difference could be a good clue too; if it's exactly a specific number of frames or some other non-video-integer value.

We'll get esoteric if/when we know more about the symptom. I love a good detective story and diagnosis.
Old 1 week ago
  #4
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They actually can be correct. It just depends on the position of the camera and the competence of the video ops... The audio from the shotgun and something plugged in can be off- usually due to the time difference of arrival between the two positions. This happens a lot in event recordings where the cameras are in the back of the room. At 25 feet,you're starting to see differences and by 35-40 (depending on frame rate) you can be a full frame out of synchronization.

Most quality video folks should be able to work around that issue and for that matter, most will go with a feed that's given because it will often be better than the crap audio they get from a shotgun mic on the camera.

The thing that's ironic in this situation is that the feed/lav/whatever is actually going to be the sound that is in sync and the mic on the camera is the sound that is out of sync.

--Ben
Old 1 week ago
  #5
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I'd advise a chat about the settings of their camera (unlikely to be the issue) and the project and ingest settings on their NLE (very likely to be the problem).
Old 1 week ago
  #6
I suspect they (or their editor) is not comfortable with aligning separate audio and video streams, if they were in fact recorded to separate devices.

Most TV studios use wired or wireless lavs and feed a single recorder a multiplexed stream of audio and video from however many cameras. Losing sync in this case requires deliberate effort in the editing bay. If separate recorders are used, as long as a proper slate is used, good quality gear will remain remarkably tight, even without unified sync. I regularly "freewheel" four prosumer cameras and audio, and when I line things up with a slate sync is good, literally, for hours. It's a far cry from when I started with analog tape for both audio and video and a BTX or other Synchronizer was $100K.
Old 1 week ago
  #7
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huub's Avatar
Quote:
Originally Posted by fifthcircle View Post
They actually can be correct. It just depends on the position of the camera and the competence of the video ops... The audio from the shotgun and something plugged in can be off- usually due to the time difference of arrival between the two positions. This happens a lot in event recordings where the cameras are in the back of the room. At 25 feet,you're starting to see differences and by 35-40 (depending on frame rate) you can be a full frame out of synchronization.

Most quality video folks should be able to work around that issue and for that matter, most will go with a feed that's given because it will often be better than the crap audio they get from a shotgun mic on the camera.

The thing that's ironic in this situation is that the feed/lav/whatever is actually going to be the sound that is in sync and the mic on the camera is the sound that is out of sync.

--Ben
Not really. If the camera is so far away, the boom/camera mic is not going to pick up any useful sound (of a person speaking).

If the mic/lav is closer, there is no time difference anyway.
Old 1 week ago
  #8
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Quote:
Originally Posted by huub View Post
Not really. If the camera is so far away, the boom/camera mic is not going to pick up any useful sound (of a person speaking).

If the mic/lav is closer, there is no time difference anyway.
Perhaps I wasn't clear... That's why I said the crap audio from the camera mic.

Once you start hitting 30 feet or so, there is quite definitely a time difference between the camera and anything else. It's physics. Good engineers will quite definitely know the difference (and should be able to see sync issues), but my point is that there are a lot of bad video people out there. I've had tons of video people try to convince me that their camera mic is better than any mic that is being fed from a recording. Videographers that will only take half a stereo mix (where there are audience mics and everythng) because their camera mic is king.

I see it all out there- and appreciate when I work with professional crews with professional gear. it makes a huge difference.

(now if we could just get good sound on to a RED camera, I'd be set, but unfortunately....)

--Ben
Old 1 week ago
  #9
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Thread Starter
I got good news today. I chanced to run into the guy who got the job of trying to learn and run all their A/V equipment, and it sounds like the gentleman I spoke to on Saturday confused a sound-quality issue with a synchronization issue. Perhaps the two issues came up around the same time or same discussion and got somewhat conflated. Life is making substantially more sense now.

Thanks for the help gents!
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