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-   -   How to Sync Audio with Video? (https://www.dvinfo.net/forum/all-things-audio/107055-how-sync-audio-video.html)

Len Rosenberg November 1st, 2007 06:22 PM

How to Sync Audio with Video?
 
If I record audio to a recorder (computer, dat, or other box) separate from the video camera, how do I combine the audio track and the video track in perfect sync? Is this what "word clock" is about? Are certain software programs better than others at this? Up till now, I have always recorded directly into the camera, but I'm looking for better quality sound. Thanks.

Edward Carlson November 1st, 2007 06:42 PM

That's what slates are for. Any sharp sound with an associated video marker will allow you to sync the audio to the video. There are cameras and recorders that will give and take external timecode, as well as some slates that show the TC, but those are very expensive. Making a clapping noise is as easy as, well, clapping.

Jay Massengill November 2nd, 2007 08:05 AM

As indicated, sycing with a sharp sound on both audio and video tracks is fairly easy on most computerized non-linear editors. The hard part is keeping all the separately recorded materials organized. It's important to keep good notes and you can do simple things such as hit record on both devices, wait for speed, then call out the camera's internal timecode numbers before you clap the slate. That will at least give you a general reference later for making sure you have the right takes together.
It's also important to record good audio on the camera even if you're using an external recorder. It makes organization and syncing easier, and can be an important backup if there's a problem with the main recorder or if the editor simply abandons the external audio because of time constraints or lack of patience.

Bill Ravens November 2nd, 2007 08:18 AM

As the other posters have written, a sharp "clap" is the simplest and cheapest way of syncing audio to video. There's some good news and some bad news with this method. While a clap gives the editor a good "signpost" to sync things up, all timers, whether they're wordclocks or timecode, are not perfect. All timers drift a wee bit so you may find that even the best crystal timers will differ by a few frames of video after extended recording times, like more than 1 hour.

The solution is to provide the "clap" at both ends of the recording, start and finish. Syncing the first clap up is easy. Syncing the second clap requires the ability to "stretch" the audio track to sync the tail up.

If you're interested in timecode generators, here's a link to one of the few TCG's on the market that works both with wordclock and VITC/LTC....
http://www.bhphotovideo.com/c/produc...Generator.html

Sassi Haham November 2nd, 2007 09:45 AM

Another one on the same topic...
 
Is there a way to slave the external recorder to the camera ?
Hit play on camera will simultaneously operate the external recorder ?
I know I can control another dv cam from my camera, why not an external recorder ? Sassi.

Bill Ravens November 2nd, 2007 10:14 AM

each camera is different. some cameras won't allow a timecode master signal in, ie you can't jam sync the camera to the TCG. consumer cams don't provide a TC signal out unless you pick it off of the VITC. no, you can't, generally, control start/stop from the TCG. your best bet with a camera that doesn't allow TC in is to use the camera as the master clock, pick the TC off the VITC(video signal) or LTC(audio track), use it to jam sync the TCG, then pick the worclock from the TCG and jam sync the standalone audio recorder.

Once again, so many consumer audio recorders have no provision for jam syncing the wordclock. Basically, TC and wordclock sync is impossible on consumer equipment.

Petri Kaipiainen November 2nd, 2007 02:43 PM

This is a bit off-topic, but the sound capabilities of a standard miniDV camera are (in theory at least) much better than the normal delivery medium, the DVD. And much better than the old movie industry workhorse, $10000+ Nagra. So adding an external recorder is not necessarily adding much quality; by using better microphones, better mic placement, better levels, maybe an external mixer feeding line-in on camera (having a camera with line-level XLR connectors) and paying more attention to audio would possibly make the audio better than getting another gadget and sync & drift problems as a bonus.

16/48 audio miniDV uses is in reality better than most people can hear, and much better than anybody can reproduce at home. First learn to use that to the fullest. Then of course there are situations where an external recorder is usefull or even mandatory, but for normal 2 mic, 2 track shooting usually not.

Bill Ravens November 2nd, 2007 04:49 PM

OTOH, if you're shooting HDv, you might as well throw that audio away. Only interview vocals are acceptable with mpeg audio compression. you can forget about quality.

Len Rosenberg November 2nd, 2007 06:21 PM

Thanks Bill, but I don't understand why audio recorded with an HD camera is inferior and should be tossed. Does it make a difference whether the camera records to HDV (like Canon XH A1) or to AVCHD (Canon HG10)? And thanks to all for the other replies.
Len

Len Rosenberg November 2nd, 2007 07:33 PM

I found the following answer to my question:

"One thing to consider is that HDV compresses audio. So regardless of how clean the A1's sound is, you still wind up with compressed MP-2 audio.

To stay within DV's data rate, the HDV codec (among other things) compresses sound to give video more bandwidth.

This is considered okay if you aren't doing a lot post production work, but if you are going to do significant sound finishing, compressed audio is not what you want to be starting out with, FWIU."

thanks.

A. J. deLange November 3rd, 2007 07:18 AM

Quote:

Originally Posted by Bill Ravens (Post 769028)
consumer cams don't provide a TC signal out unless you pick it off of the VITC. no, you can't, generally, control start/stop from the TCG. ....
Basically, TC and wordclock sync is impossible on consumer equipment.

Some consumer (or prosumer really I suppose) cameras such as the Canon XL series (and I don't know about their others such as the new HD offerings though it is reasonable to suppose that they probably do) provide time code through the LANC port. This can be converted to MIDI time code with the proper adapter cable and thence to LTC with appropriate equipment.

One can always derive sync from the camera's video output but again proper equipment is required. Thus if you are willing to lug a MOTU Timepiece (or similar gadget) about with you (and figure out how to power it) you can obtain a word clock from any consumer camera which has a video output and thus record synchronized audio on any device which accepts word clock. You would still have to do the alignment manually (no TC) but that is quite simple if the audio and video streams are running at exactly the same rate.

Tim OBrien November 6th, 2007 09:47 PM

I recorded a combo DVDvideo and music CD last year of my father-in-law singing some of his original and country-music songs as a rememberance for the family.

Video using a GL-2. Audio was an M-Audio Solaris on his vocal and an SM-57 on the guitar amp recorded into my laptop music DAW in Cubase on separate channels (so that effects, eq'ing, etc could be applied separately). I also used the hand-clapping 'slate' trick.

ZERO problems with sync throughout the evening.

Big Hint: Record the audio in 48k sample rate (the standard for video) and it'll all sync up when you bring it into your video editor.

I recorded the audio in 24-bit/48k to get a better quality for the audio CD, then after mastering I downsampled to 16-bit/48k to bring into Vegas.
(of course the final files for the audio cd had to be downsampled to 16bit/44.1khz for final burning, but thats not a problem.)

Peter Moretti November 6th, 2007 10:14 PM

If you are willing to loose an audio channel on the camera's recording, can't you run a timecode recorder's LTC into the one of the camera's audio tracks?

That will give you true timecode to synch with, no?

Seth Bloombaum November 7th, 2007 01:21 AM

Yes it will. But then, how do you use it in post? AFAIK, there are no LTC-friendly TC readers for NLEs, maybe there's one for AVID?

Without NLE support you'd have to take that audio channel output from your computer out to an external TC reader... account for any audio latency & apply correction... and and and...

Better with rough time-of-day TC sync and reference audio on the camera for fine sync, I think.


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