Audio Drift - Marantz 661 External Recorder and Panasonic GH2

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xocomil

Well-known member
Recorded a few interviews the other day and have discovered something very odd. When trying to synch up audio from the camera with audio from the external recorder I get a pretty serious progressive audio drift from the recorder. I haven't had this issue on previous interviews and am wondering what has changed.


What is most troubling is that after synching with pluraleyes, the audio waveforms match up perfectly, but the audio from the Marantz don't actually match the Marantz's waveforms as seen in FCP's timeline. Audio synchs initally but drifts as the interview continues.


Using Panasonic GH2 (hacked) N American version filming in 50i.


Any ideas?

PS - I've also posted this in the Panasonic GH thread
 
That is the nature of using two separate devices that do not sync together. Long takes are the enemy of lower end equipment. The problem could be both the camera and the recorder, or either. It is not just the recorder that could be suspect. The Marantz could be spot on, and the camera drifted.

Unless you can tie the devices together through timecode sync (must be able to), you will always have to plan for drift with long takes. On short takes, the issue is not really noticeable, but once you go a few minutes (sometimes less) it starts to get progressively worse.

Two options: Plan for this by having "cut points" and insert something to allow for a resync.

Or get equipment that can be sync'ed together with TC.
 
Somebody on YouTube did tests recently (very very precise ones) and found that a new Tascam DR680 recorder had less audio drift than a Canon DSLR - yes, the DSLR had more drift recording internally alongside it's own pictures!!!

So I agree with Doc that it could be the GH2 that is drifiting. Make sure that you have the settings matched! Make sure you record in 16/48 or 24/48. If you record in 41.1 you are asking for trouble. Your project settings for audio must match the recording settings too. Check that!
 
Thanks gentlemen.

What was strange was that this issue hasn't cropped up before, even with 20/30 minute interviews.

I'll check my settings to make sure they match. And will make sure longer interviews have a pause every few minutes to allow for re-synch.
 
xocomil said:
Thanks gentlemen.

What was strange was that this issue hasn't cropped up before, even with 20/30 minute interviews.

I'll check my settings to make sure they match. And will make sure longer interviews have a pause every few minutes to allow for re-synch.
Click to expand...

You mentioned 'hacked G2', were the previous interviews shot with the same hack? Also, was the temperature of the interview about the same as previously... Temperature may affect some crystal/timing circuits, and the hack may be 'heating up' the camera more... that of course is a wild thought... but that's what occurs to me frequently when 'things use to work, and now they are different' situations.

In any case, the advice to have 'cutaway' points, to hide any resynchronization, is a requirement for shooting with devices that are not locked to each other.
 
Luxas - My Panasonic GH2 audio is recorded at 48. In the event that I set my recorder wrong (to 44.1), can I adjust the length when editing within Premiere Pro? Or, should I use something like Audition, and process the file to match sample rates.

I haven't experienced any sync issues, but my shot length is typically under 3 to 4 minutes. I suppose with longer clips the sync issue will become evident. Stupid me...I hadn't given this more thought, but fortunately, my recorders (Tascam DR-680 and DR-40) are usually set to 48.



Lucas Adamson said:
Somebody on YouTube did tests recently (very very precise ones) and found that a new Tascam DR680 recorder had less audio drift than a Canon DSLR - yes, the DSLR had more drift recording internally alongside it's own pictures!!!

So I agree with Doc that it could be the GH2 that is drifiting. Make sure that you have the settings matched! Make sure you record in 16/48 or 24/48. If you record in 41.1 you are asking for trouble. Your project settings for audio must match the recording settings too. Check that!
Click to expand...
 
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Steve - Thanks for the tip.

Q: Premiere Pro is able to work with video footage of different frame rates. Does this not apply to audio with different sample rates?

I use PluralEyes for sync'ing my recorder audio to my camera audio. It seems to stay in sync, but as my clips are typically short (3 to 5 minutes) I haven't notice sync problems. I'm just curious if audio from cameras and audio recorders with different sample rates will have sync problems, or other issues, with my work flow.

Steve House said:
You need to convert the sample rate of the audio file to 48kHz. Just load it into Audition and use 'convert sample type' from the edit menu
Click to expand...
 
RE: OP

Since there wasn't an answer to his question and it might be of interest to others. FCP has a "bug" of sorts. Even when you are all file based it will make some assumptions based on the capture settings. The classic is someone who normally works in NTSC and then shoots something on a DSLR at a whole frame rate, like 25 or a true 30 or a true 24 and then imports the footage (with out changing the capture settings to match the new frame rate). Once that happens there is no easy fix that I know of. FCP will assume you shot on film and have pulled it down to video speeds. The audio that came in with the video is fine because it came in with the video BUT all audio you add after that will get "pulled down" and play out of sync. It's a nightmare for sound post because typically it doesn't get caught in the picture edit unless there are some long takes (it's only a 0.1% speed shift) so it gets passed off to sound post. Programs like proTools don't make silly assumptions like this so it's all fine in post till you send the mix back to FCP. Now you have a "take" that is the length of the film and even though 0.1% is not a lot it's three seconds over an hour and that IS a lot.

The only "fix" I know of is you can wrap the sound in a Quicktime with a bogus frame rate so that FCP will leave it alone.

FCPX may not have this issue but since you can't send projects to sound post if your using FCPX (no export capabilities) it's kind of a moot issue.


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RE: the later poster with the sample rate issue.

You probably should but may not need to convert the sample rate. Old school you would have no choice but these days most of the NLE's can sample rate convert on the fly, and seem to do so quite well. It's more overhead for your computer so if you are having playback issues then ...

Also if you are going to sound post you will probably have to convert at some point. Few DAW's like or will accept mixed sample rates and I don't think it's allowed in the OMF spec.? not sure on that, but point is you are safer converting if you are planning to go outside your box for sound.

If you are doing it all on your own system AND you are not having drift issues then I would probably just leave it be.
 
SK - Thanks! I have dealt with sample rate conversions in ProTools (and seen the problems it will cause if ignored), but as audio drift hasn't been apparent within Premiere Pro, I hadn't given it much thought. I will be more attentive in the future!
 
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