Ensuring audio doesn't slip sync?

D

DCalson

New member
Hi,

I'm filming a band in a recording studio. Using DSLRs. Anyways, the audio will be recorded separately by the engineer in the booth. I've never done anything like this and I was wondering, is there anything I need to do special to ensure the audio they record will stay in sync with the video I record?
 
At the simplest level make absolutely sure that your dslrs are recording the audio as well so that you can synch up later using Plural Eyes or the multicam syncing in FCPX for instance. The software compares the waveform of the dslr audio with the waveform of the reference audio in order to perform the synch.
 
It really depends how long your takes are going to be. If you will stop the recording between songs then you should not get much if any measurable drift. Longer than 10 minutes and it might be apparent and need some timeline sliding in post. As usual, do not know the budget and if it is a pro job where folks need it to be done right. You could run a word clock device which is fed a camera signal which in turn controls the recoding studio's equipment timing. Basically using the video signal as the master. But this needs some equipment and a studio willing to work with you.

You could stop by and do a test beforehand with a 20 minute run just to see where you stand. It might be fine or it could be awful.
 
Bassman2003 said:
It really depends how long your takes are going to be. If you will stop the recording between songs then you should not get much if any measurable drift. Longer than 10 minutes and it might be apparent and need some timeline sliding in post. As usual, do not know the budget and if it is a pro job where folks need it to be done right. You could run a word clock device which is fed a camera signal which in turn controls the recoding studio's equipment timing. Basically using the video signal as the master. But this needs some equipment and a studio willing to work with you.

You could stop by and do a test beforehand with a 20 minute run just to see where you stand. It might be fine or it could be awful.
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What Bassman said. I am editing a two camera shoot we did in San Francisco last month with a pro sound mixer. We shot with two C200s, which just like your DSLRs, don't have time code i/o so we used a dumb slate. I am editing with Multicam in FCP X 10.4.4 and using it's auto sync capability, the sync is working great, I make a multicam clip using the sound mixer's BWAV and I can shoose from the main mix or any of the ISO tracks on the talent. But we were only doing 2-4 miute takes since this is scripted scenarios with actors. If you want to make sure that you stay in sync and are doing takes more than 5-10 minutes without stopping, I would rent or buy some Tentacle Sync E


They seem to work pretty well. When working with non-TC capable devices, the amount they slip/lose sync varies a lot. Generally, the cheaper the device, the more they slip in sync but not always. Shooting some tests beforehand is highly advised so you know what you are working with.
 
I can only relate my experience but I have made quite a few multi cams with four or five Nikon D4 DSLR's and a Sony FS5 with some clips running over an hour and using FCPX have yet to experience any drift. Reference audio was recorded on a Sound Devices 722 but no timecode was used.
 
Many ways to do this. Some require money, some require discipline.
(well, all require discipline, but this wording is more aphoristic)

So in addition to the approaches above, you could do this the way many live concerts were recorded "back in the day" and still today.

Every 15-20 minutes point all the cameras at a dumb slate that's near one of the studio microphones and clap it.

Change camera batteries on a regular schedule (depending on cameras & batts... say when batts are down to about 25 to 20 percent) mainly to ensure a camera doesn't go down during a really great bit and then come back up without a close-to-the-others take start.

Or rent and have a timecode slate (or big TC clock display) running somewhere in the studio, but mostly out of site of what you'll be filming. Like at near the floor by an amp or wherever. Then every 10-20 minutes, make sure each camera records five seconds of the slate in focus so you can read the numbers.

Have someone take good notes so you know what TC goes with what bit (though that'll be pretty obvious, I think). And have that person remind all the camera ops to record the dumb slate and/or the TC slate/clock.

Hope they have a drummer who hits big so you'll have easy-to-see tight sync points if you need them, once you have things fairly close.

You could go for waveform sync (ie- PluralEyes and the like), but if it's a loud rock band, the camera mics might just be clipped the whole time and there might not be good enough waveforms for the software to sync to. So if you want to head down that path, do a test and/or have a backup system just in case (ie- slates).

So basically, you'll be kicking the job to post. But I'm assuming you'll have mostly long takes, so this won't be an impossible task. Done this a bunch. Timecode on every cameras and on a track of the audio mix is totally nice, but you can get away without it.

Good luck and let us know what you end up doing!
 
I think in general, there has been a convergence In recent times and audio gear makers are aware of video uses. So things seems to work better together than they used to. I recorded an entire dance show with a Marantz 660 and it kept amazing sync with my video cameras. I was shocked.
 
There are two things that people refer to when they talk sync and often the two get confused.

First there is positional sync. A way that after the fact you can find takes on different gear that belong together. Time Code is great for that but the audio sync functions in many EDL's are also very good these days. This will get all of your sources to start in sync.

To stay in sync you need the clocks to be running at the same speed. With an all analog system you could use TC for that also, but not with digital files. With digital tape you needed to make every thing work off the same clock to get much consistency. That requires hooking up word clock between everything and having everyone slave to a master clock. With digital files and recent equipment the clocks in gear have become very stable and quite accurate even on fairly consumer gear. So as others have said anything under 10 min. or so you are very unlikely to see any noticeable drift. Most gear is probably good to within a frame an hour or so.

You are going to be cutting between cameras so your worst case situation is to need to adjust sync slightly on a cut.
 
Hey everyone,

Thanks for your replies. Lots of valuable info. For this project, I'm going to film a 3 min song, stop, film another 3 min song, stop, and so forth. Hopefully that's a short enough time not to drift. But yeah, I'll definitely look into all of these options. Also, doe sample rate, bit depth on the audio recording device matter much when keeping things in sync?
 
Typically the audio sample rate in sound-for-picture is 48kHz and most defiantly use PCM files until you can't (i.e., MP4 web video or space constant on a DVD). The bit depth does not affect sync, 24 or even 16 bit would be sufficient if it's being initially recorded by pros.
 
Just to repeat what Rick wrote (in slightly stronger language)...

Ask the studio engineer to choose a recording format best for video, such as:
24 bit, 48KHz
16 bit, 48KHz

You *really* want to avoid starting out with a recording at 44.1KHz!

Once you start cameras rolling, do not stop until the end of the take. This cuts way down on the number of syncs you have to perform. Many shooters will think they should just roll when they have the shot composed the way they want it, but shooting music with multiple cameras is a little different.

Some of the earliest budget sync methods involved all cameras shooting a clock with a sweep second hand, and keeping them rolling through to the end, or, if they had to reload, shoot the clock at the beginning of every reel/tape.

Some DSLRs are capable of free-run timecode. For this, you can use Time-of-Day timecode. With a little practice you can get each devices internal timecode generator running at better than a half-second sync resolution. Which will get you close in post, close enough that fine sync can be done by hand.

And, as written above, all cameras should record sound. You could have the studio engineer send a bloop (a short tone) to all monitors and all recorders once you have all the cams rolling. That will help a LOT, even if the rest of the camera sound recording is overdriven to distortion.

You’ll need to explore whatever multicamera editing methods your NLE provides. At worst, one camera per track and switch using a razor tool. Brute force, but it’s solid, it works. Most NLEs provide something more elegant...

There are methods. Not as solid as Tentacle sync boxes everywhere, but, with some thought, practice, and trial and error you can make it work! Just expect that your first 25 hand post-syncs will be hard, the next 25 you’ll say “that wasn’t so bad”, and after a hundred you’ll wonder what all the fuss was about!
 
Over the past 8 weeks I've been recording multiple cameras in theatre shows - and two of them are locked off and difficult to access, so they start to run at maybe 20 mins to show time, and then get collected 3 hours later. Audio from a Zoom connected to the house PA mixer. Manually synced to a suitable even at the start (the drummers first cymbal crash, visible in every camera), none of the cameras needed re-syncing for the duration of the events In fact, the only niggle was the extra syncing for the cameras that stopped during the interval.

I firmly believe that speed stability in terms of fps and the digital frame rate are now so stable that the old drift issues are gone. The real pain were the few Chinese Go-pro-esque cameras that we dotted around that do NOT have UK frame rates, i.e. only 30/60fps rates. Converting to 25/50 seems to always cause some drift, end- to end. I wonder if it's the cameras drifting, or something introduced in the conversion process?
 
SethB said:
Some DSLRs are capable of free-run timecode. For this, you can use Time-of-Day timecode. With a little practice you can get each devices internal timecode generator running at better than a half-second sync resolution. Which will get you close in post, close enough that fine sync can be done by hand.
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A minor correction for clarities sake. Most (all) DSLR's time stamp files and that can be used as described above. But that is not "time code", at least not what people refer to when they talk about Time Code, it is just a time stamp in hours minutes and seconds.

The key difference being that TC is frame rate referenced and has user bits and a time stamp has neither. For the use described that doesn't really matter but in other uses the difference is important.
 
Noiz2 said:
A minor correction for clarities sake. Most (all) DSLR's time stamp files and that can be used as described above. But that is not "time code", at least not what people refer to when they talk about Time Code, it is just a time stamp in hours minutes and seconds.
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Except that cameras like the GH4/GH5/GH5S do use time code. Technically, those are mirrorless rather than DSLR, but “DSLR” has almost become a blanket term like “Q-Tip” or “Kleenex”.

The GH4 had that big, clumsy adapter that added XLR audio inputs and a BNC connection for TC sync.

The GH5S has a BNC cable available for TC sync, and it attaches straight to the camera body.
 
Interesting. You are right that they are not not DSLR's lacking the R, and yes people do use the term incorrectly a bunch.
Even Panasonic describes them as hybrid still/ film cameras so the TC functions make sense and I didn't know they had them. Though it's a bit crippled in that according to tenicle only the last one can be jammed, though it sounds like the adapter, you mention must allow the G4 to jam?
There is also apparently an ap that will let you sync the TC generator on multiple GH4-5's and that would certainly work for the OP.

But do any other DSL (R)'s have TC functions? Blackmagic does but they don't even pretend to be a still camera.
ML has some TC functions but they seem to be problematic.

My point was a bit like calling a mirrorless camera a DSLR. In most cases it doesn't really matter BUT in some cases it adds a lot of confusion. So I personally feel it's important to use the correct terms for things whenever possible.

I had an argument with a video producer we were doing post for. He had sent us 3/4" a cassette (yep not recently) that didn't have any TC on it only the tape counter. He insisted that thetape had TC. We didn't care because we were digitizing everything then and we didn't need to sync to the tape. I was giving him a heads up that the mix stage would not be able to use a tape that had no TC on it. He had been doing this for years bla, bla, bla... So we sent our files off to the stage and the guy showed up with a tape and... it had no TC so he got to pay for the stage while he went back to the shop to make a new tape that did have TC on it.

The tape did have a TC format counter but it was not TC. So while there are apparently a few cameras that do have actual TC most DSLR's and most mirrorless cameras don't. And what the poster was talking about was clearly for cameras that didn't. And calling that TC can get you into trouble for uses other than what he was suggesting.

As a positional reference, unless you can jam sync everyone, it doesn't really matter if the camera is time stamping or stamping TC. Either way with out being able to jam you are only getting info of about where the two files should sync.

But I am glad to hear about the GH5S, because I have a shooter I work with sometimes and he has one I think and I don't think he thought about it but we could jam and make his post life a bit easier.
 
paulears said:
Over the past 8 weeks I've been recording multiple cameras in theatre shows...
I firmly believe that speed stability in terms of fps and the digital frame rate are now so stable that the old drift issues are gone...
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Having done a lot of hand-syncing over the years, I completely agree with this, even for hour-long takes. Of course there’s someone with some contrary experiences, perhaps with different cams or recorders than we’ve happened to be using, but digital technology has made a huge difference. (Man I feel like a dinosaur when I say/write stuff like that!)

Noiz2 said:
A minor correction for clarities sake. Most (all) DSLR's time stamp files and that can be used as described above. But that is not "time code", at least not what people refer to when they talk about Time Code, it is just a time stamp in hours minutes and seconds.

The key difference being that TC is frame rate referenced and has user bits and a time stamp has neither. For the use described that doesn't really matter but in other uses the difference is important.
Click to expand...
Quite right, thanks for the clarification. We’re talking a single timestamp in the file header...
 
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