Audio - Video keep going out of sync

W

wakayoda

Member
Previously I have made use of a stereo recording from a Zoom H4 and then matched that up to multiple video tracks, dealing with live music here so I would see this as being one "scene".

Before I have had no issues with the audio slowly going out of sync at any part of the composition, but now I have after making use of audio recorded from a FireWire mixer on eight channels to Cubase.

After exporting each channel as a 44100 HZ mono WAV file, all the sound is in sync at both the start and end of the composition; but with the video I sync it all up at the start then go to ten minutes in and find that its out of sync by over two seconds - at the start it is in sync by the waveform working audibly with no echo like effect.

What do you make of this?

Cheers!
 
I haven't used Cubase before, so I have to ask this.

Does cubase allow you to set up a session at a certain frame rate. In Pro Tools, for example, I can run a session at 29.97, or 24, or 30. If you can do this in Cubase (again, i'm not sure of this), and the frame rate is different from what you were recording on the camera, then you will see drift.

If Cubase has no frame rate setting, then maybe there is a setting that was on the firewire interface that caused this?

The reason I say this is that 9 times out of 10 that I've seen audio drift issues like this is because of a frame rate issue.
 
I've just asked my friend that handled the audio recording that question.

I'm putting the audio with the video in Premier Pro CS5.
 
If you're recording for video, always always always use a 48kHz sample rate, not 44.1. 48kHz is the video standard, 44.1 is the standard for audio CDs. While I can't positively say this is the source of your specific trouble, when it is dropped into a video timeline a 44.1kHz file must be converted to the video standard of 48kHz and something goes haywire with the conversion, the result will be exactly the sync problems you describe. Try converting the file to the proper sample rate before importing and syncing it to the video.
 
Steve House said:
If you're recording for video, always always always use a 48kHz sample rate, not 44.1. 48kHz is the video standard, 44.1 is the standard for audio CDs. While I can't positively say this is the source of your specific trouble, when it is dropped into a video timeline a 44.1kHz file must be converted to the video standard of 48kHz and something goes haywire with the conversion, the result will be exactly the sync problems you describe. Try converting the file to the proper sample rate before importing and syncing it to the video.
Click to expand...

then will 96Khz cause any problem?
 
Sample rates "should" not make a sync difference IF they are converted. That said the less conversion you need to the less chance for having a problem.
It the old days what you describe was usually a clocking error. Actually it probably still is. But since nothing was clocked together on recording???

PP should do a good job of handling media (FCP can cause this if your footage is at 30 or 24 fps) so I suspect that either your video or your audio recorders was running a bit fast or slow. But how much drift are we talking? A clocking error is going to be a very small drift so it should take a long time to get far off. If your drift is 3 sec/hr then it's time to look at a film speed VS video speed issue (assuming your in NTSC land). This could happen for instance if you shot at 24fps and dragged the footage with out conversion into a 23.98 time line.

If it's not an oops then you need to look at either re-syncing periodically or time stretching (shrinking) the whole file to fit the video.

___________________

96k as a rule will have that same conversion stage possible issue. Depending on what your final format is you have to ask your self why your recording at 96k. If your heading to DVD then it's a big waste of bandwidth. It's probably a waste anyway but it really depends on what your recording, what your recording with and what your recording for. If your recording rig is a lot below say $30K then you are probably not recording anything but high quality noise with the extra bandwidth. If your going only to DVD or WEB or broadcast it's a waste because any nuance you managed to capture will be squashed away. If your recording loud events or things with out a lot of fine detail in the high end it's also a waste.

If it's a live recording destined to get remastered to CD then maybe it's a good idea.
 
Steve House said:
Not as long as you're sure it's properly converted to 48kHz when you add it to the timeline.
Click to expand...
thanks! what if my video frame rate is 23.976? do i need to slow down the 48kHz audio 1% to 47.952kHz? because I'm worried that the sound may drift in some very long footage.
 
No. Your shooting at "video speed" and your footage is not going to change speed in editing so it should play in "real time". Your 48K audio will play back also in real time so as long as the two were clocked reasonably accurately your fine.
Consumer devices clocks are not necessarily super accurate so they can drift over time. If your doing narrative films that is rarely an issue since your takes are so short. Even doc don't usually have takes over 20 min or so. Concert recordings where you might be running over an hour with no break start to get dodgy.

FYI what your are suggesting wouldn't work anyway because your hardware is clocked at 48k so you would actually speed up the sound by that change. Also you meant %0.1.
The old school method was to record at a higher sample rate so it would play back slowed down at 48K.

BUT that is only used if you are shooting at a FILM frame rate (24 (NOT 24p) or a true 30) "film speed" and editing at 23.98 or 29.97 "video speed".
As long as you stay at the same "speed" you don't want to change the "speed" of your sound either.
 
marvinhello said:
thanks! what if my video frame rate is 23.976? do i need to slow down the 48kHz audio 1% to 47.952kHz? because I'm worried that the sound may drift in some very long footage.
Click to expand...

Q though. Your in PAL land so why are you shooting at a NTSC frame rate?
 
If you are editing "multiple video tracks", why wouldn't you just "pull-up" the video to match the audio at each video edit point. That's what I do. It is so trivial I don't even think about it. Or are we missing something here?
 
Steve House said:
If you're recording for video, always always always use a 48kHz sample rate, not 44.1. 48kHz is the video standard, 44.1 is the standard for audio CDs. While I can't positively say this is the source of your specific trouble, when it is dropped into a video timeline a 44.1kHz file must be converted to the video standard of 48kHz and something goes haywire with the conversion, the result will be exactly the sync problems you describe. Try converting the file to the proper sample rate before importing and syncing it to the video.
Click to expand...

Just tried with the converted 44.1KHZ to 48KHZ and it now works, straying in sync for the whole 50 minutes! - I can' thank you enough!

Richard Crowley said:
If you are editing "multiple video tracks", why wouldn't you just "pull-up" the video to match the audio at each video edit point. That's what I do. It is so trivial I don't even think about it. Or are we missing something here?
Click to expand...

Ahh I see what you mean, I didn't explain it properly really - I have 7 video tracks and 8 audio tracks, its a band live performance shoot so every track has to in sync constantly.
 
marvinhello said:
thank you for the tip, because the "film look" 24p in DSLR is actually 23.976
Click to expand...

OK but if your going to edit in a PAL timeline you are going to have some serious sync issues. 23.976 to 25 is a big speed change. Of course Europe, being more civilized than the US, is much more format friendly so you could probably just stay NTSC and 90% of the DVD players wold play it fine.

If you want real irony a typical NTSC "film look" trick before 23.98 was common was to shoot in PAL. 25 fps looks about the same as 24 fps.
 
wakayoda said:
I have 7 video tracks and 8 audio tracks
Click to expand...

I don't understand that part. What are these "8 audio tracks"?

Is this an 8-track recording that needs to be mixed-down to a final mix? Is it the live track from the microphone on each camera?

My method is to take the final, mixed-down audio track and lay it into the timeline FIRST. That mixed-down audio track is the MASTER REFERENCE for the production.
Then I take the video clips from each camera and lay them into the timeline in sync with the master mixed-down audio track.
I use the microphone audio from the camera clips to align them to the master audio track, and then I mute the camera audio because they are useful only for sync/alignment.
The sound tracks from the cameras are never used in the final video cut.
 
Your khz , i think thats the problem, I used to record 44.1 k from H4N, and using a 48k timeline... at the begining of the audio is ok, but if you have a long piece, it starting going slow ... unsync around 2 second......

So...I guess you should sync yourself or match the 44.1k to whatever you are aiming to edit with.

Good luck

Hiro
 
@Richard

I have 7 camera angles each with audio either in mono or stereo, then 7 audio tracks consisting of mono sound for everything and 1 stereo for the cymbal over heads.

I always end up using the audio from the camera as it helps to thicken out the sound resulting in a more "I was there" sound, typically I would only have a stereo mix from the desk so :D

@Hiro

I'm going to have to re-export from Cubase at 48K, I've tried to match it up every now and then but becomes too noticeable after 3 minutes.
 
I think you are missing my point. Perhaps I did not make it clear enough.

1) Start with a good AUDIO MIX of the program. You can use whatever sources you wish (including audio tracks from video cameras, etc.).
Yes, of course, you typically need some ambient microphones in addition to the "dry" feed from the FOH mix. And the tracks from the camera mics may be perfectly good enough for that kind of "ambient" or "audience" sounds.
2) Lay that master audio mix into the video edit timeline FIRST. That is your MASTER REFERENCE for everything else.
3) Drop your video clips into the timeline and align each to your master reference audio mix.
4) Mute (or delete) the audio tracks from the cameras. If you did (1) properly, you only need them temporarily for alignnemtnt (3) and then you can dump them.
 
I had an H4 (not H4N) and it had terrible drift. You may want to try a firmware update, but I eventually sold mine as I couldn't even record 5 minutes without the audio drifting too far from the camera audio.
 
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