Audio drops out on printed dv tape

[Jonathan Jones]

Forgive me if this ends up having been posted to the wrong section. It seems like a complex problem with which I have had no experience. But somewhere in the mess it involves a DVX100, wireless lav, cutting on a Mac in Final Cut Express, and final output printing to dvtape. The problem referenced below could possibly have arisen anywhere within this chain, and could consequently belong in different forums, but since it's basically audio, I'm gonna post here.

I got an email from a friend who shoots weddings, but doesn't have a lot of the technical expertise to troubleshoot such errors as what she is currently having a problem with.

She shoots weddings on a DVX100, generally using on-cam mic for general audio, group activities, receptions, etc, and using a wireless lav plugged into the cam for the wedding ceremony, specifically to pick up the vows.

She takes the footage into Final Cut Express on her Mac and edits it together, and then prints the whole timeline to a DV tape to send out to some type of post facility to have it put onto DVDs for her clients.

Evidently, with her most recent wedding video, the post facility noted that there was missing audio from the tape. It was taken to a few other facilities and tried in different decks, but the same thing occurred in some machines, but played okay in others. The resulting DVDs were all affected by the dropout of the wireless lav track.

Eventually, she narrowed it down to the fact that the affected audio pertained to only the segments in which the audio was recorded using the wireless lav.

As the video gets to any audio clip on which the wireless lav was present in the mix, the audio dropped out. BUT THE VU METERS CONTINUED TO REGISTER THE SIGNAL, although nothing could be heard.

She couldn't figure out the problem because everything continues to play fine on her Mac. The timeline plays fine in FCE. She exported the timeline to a self-contained Quicktime mov file and the audio played fine in there. She exported the timeline again to DV tape using her DVX as a deck and it printed fine, and the DVX played it back fine with the audio fully intact.

She then went back and played the DVDs from the last several weddings she edited and found that the DVDs from the last 5 weddings are similarly affected..... although evidently none of the clients ever made mention of the problem to her.

So she's been in a panic and feeling overwhelmed about this problem and doesn't know how to fix it. She doesn't know if it will be even possible to recut and repair the earlier productions, but she is curious as to whether she has something set wrong somewhere that is causing the vow audio to drop out for all of her weddings.

Does anyone in these forums have any familiarity with such an anomaly? I will be happy to pass any info anyone can offer on to her and see if she can resolve it. It's been years since I've shot on a DVX and I never fiddled around with the audio settings on it.

I have otherwise never had such an experience myself and don't know where to begin trouble-shooting her problem.

Thanks for any insights y'all may offer.

I will include points from her original email to me below.

-Jon



------------------

From my friend's email describing her audio problem;

"Has anyone ever had this problem??

You videotape a wedding like you always do.......... .2 cameras with one wireless mic on the groom, you have it edited the way you always do - Final Cut, the master of the video gets transferred onto a mini-DV tape for the Master Tape and this situation has always worked perfectly (for years)...... ...until now.

what could have gone wrong if this is happening?

What things could have changed perhaps by accident and maybe not noticed to cause this; at any stage of the process..... ......the camera, the computer, the duplicating equipment??

The final Final Cut version in computer of the wedding has perfect sound.
The mini-dv Master copy made here has perfect sound.
It has perfect sound when played on an both DVX cams here.

BUT

in sending it out to be transferred to DVDs - no one has been able to do it, AND
it plays differently in different DV cameras and decks! So far it has been tried in at least
9 machines.... .including a DVCam machine at the Oakland Raiders Media Room and at KTVU Ch.2.

In some machines you can hear the vows perfectly (where the wireless is in use) and other machines you can't. In some machines the sound
drops off completely - although vu meters shows there is sound.


What is going on?!


S.O.S.!!!!!"

[Dean Sensui]

I would suggest exporting a NTSC DV-format Quicktime file onto a portable Firewire drive, and creating a DVD from that with iDVD. It would save your friend the cost of having a third party author the DVD and the procedure is fairly simple.

Or see if the facility will take a file on a hard drive, rather than tape. It would save them the trouble of digitizing, and also avoid any problems with tape.

[Steve House]

For future prevention, suggest she check the head alignment and the transport on her camera. I doubt it's the wireless lav per se that is the cause since the audio is there, no dropouts on some decks but present when played on others. That suggests the problem is going to be present with any audio recorded to that channel, regardless of its source. That sounds like a camera problem where it's out of tolerance enough that the resulting tapes are close to the edge, playable on some decks but not on others.

[Daniel Epstein]

Yes it does sound like her DV cameras are out of spec compared to the decks being used elsewhere. I had similar problems with a client who had a Sony DSR-11 which had this problem with some DV tapes but not when we used DVCAM.

[Jonathan Jones]

Thanks folks, for your insights and suggestions. I have passed them on to my friend who has continued to work with the problem, but her ongoing problems seem to get even more confusing.

Up to this point, it was making sense to me that the fault point would be with camera and having the heads out of alignment.

As far as making the DVDs on her own, I followed up with her on this, and it turns out that she had subcontracted with another vendor to shoot and edit the content for that company, and they requested that she provide the content on tape from which they would master DVDs themselves, or through their own preferred post facilities.

So she ended up burning the content to a DVD herself, using the full-quality self-contained Quicktime .mov file from which she could hear the questionable audio just fine.

She then played the DVD back after having burned it, and surprisingly, the noted audio dropouts occurred on her own DVD as well.

Because the content audio plays fine in her timeline, and in her QT export, and in her cam, she is now completely perplexed about why she is now experiencing the dropouts on her DVD in the same way her client has with the master tape in other decks.

Is there a possibility that she is experiencing a phase conflict that was generated by an improper setting or something broken in the wireless lav - or even still with the head alignment of the cam, that would cause one channel of the questionable audio to cancel out the other entirely....but that for some reason wouldn't be noticeable in some forms of the content presentation (such as her timeline, etc)?

I asked her to listen to the audio portion in question with the Quicktime video on her Mac, while monitoring it through a pair of headphones, and she stated that it sound fine in the cans, and came through properly balanced across the stereo field as she had intended.

Yet when the mastered tape is played back on a deck that is not hers, the audio in question is completely missing, although the VU meters continue the register the audio.

I'm thinking the cam heads idea may still be the potential problem, but I can't figure out why she would still be able to hear the QT file fine on her Mac, but then have the problem continue to occur on a DVD that was created from that QT file.

Further insights are much appreciated, and I thank you very much for your thoughts thus far.

-Jon

[Pete Cofrancesco]

I find that odd problems tend to occur when one uses an odd process. I'd tend to agree that the problem lies with writing video back out to the camera. There are so many reasons not to do this:

1. Quality loss: filming in a highly compressed format (dv) then re-compressing to dv again, reimporting it and then encoding it to mpeg2?
2. Its so easy to author your own dvds why would you pay someone to do it?
3. Why would you want to use you camera as a deck and risk wearing it out. She films with the camera drive, then imports using it, then exports using. Hmmm I wonder why its not working properly...
4. Every time you write out to tape you risk drop frames especially if she's not using new tapes but even if she is I wouldn't risk something as important as a wedding.
5. Long process to write out at real time to tape then the time for someone to import that again at real time.

[Chris Soucy]

OK, lets ditch the analogue stuff here - it's digital, it either plays or it doesn't, there's no such thing as "gracefull degradation".

Head alignment means exactly the above - one out, all out.

It isn't a head problem.

In order to lose just the lav audio when it plays perfectly just about everywhere, the lav track must be being stuck on both channels but inverted to make it cancel out.

The question is - where?

Two cameras - right?

What audio is going into both - exactly?

Two channels on each?

Makes 4 channels of audio - correct?

What feeds?

Is the lav split on one camera and fed to both channels (the dubious Y cable syndrome)?

Yada, yada, you can probably see where this is going - if 4 channels are getting mixed down to 2 and the lav is on 2 channels.....................somehow it's getting inverted and hey presto, it's gone during the transfer process.

I can see how the inverted signals would play perfectly under some codecs and vanish in others depending on how they handle the merged data.

Think the connection of the lav to the camera concerned needs to be checked, after all, cables wear and need to be replaced.................

Make any sense?


CS

[Steve House]

Sounds like a case of inverted phase on one channel. Plays fine when stereo but cancels when downmixed to mono.

[Daniel Epstein]

It does sound like the people who can hear the signal are monitoring in Stereo and the people who can't hear the signal are monitoring in Mono. If she edits the piece in stereo and monitors in stereo she wouldn't hear the problem in the edit. This usually occurs when one source is recorded to two tracks but the tracks are out of phase and cancel rather than add. She should be able to fix it in edit. Use one track centered rather than two tracks left right

Originally Posted by Jonathan Jones

Eventually, she narrowed it down to the fact that the affected audio pertained to only the segments in which the audio was recorded using the wireless lav.

As the video gets to any audio clip on which the wireless lav was present in the mix, the audio dropped out. BUT THE VU METERS CONTINUED TO REGISTER THE SIGNAL, although nothing could be heard.

She couldn't figure out the problem because everything continues to play fine on her Mac. The timeline plays fine in FCE. She exported the timeline to a self-contained Quicktime mov file and the audio played fine in there. She exported the timeline again to DV tape using her DVX as a deck and it printed fine, and the DVX played it back fine with the audio fully intact.

She then went back and played the DVDs from the last several weddings she edited and found that the DVDs from the last 5 weddings are similarly affected..... although evidently none of the clients ever made mention of the problem to her.

So she's been in a panic and feeling overwhelmed about this problem and doesn't know how to fix it. She doesn't know if it will be even possible to recut and repair the earlier productions, but she is curious as to whether she has something set wrong somewhere that is causing the vow audio to drop out for all of her weddings.

Does anyone in these forums have any familiarity with such an anomaly? I will be happy to pass any info anyone can offer on to her and see if she can resolve it. It's been years since I've shot on a DVX and I never fiddled around with the audio settings on it.

[Jonathan Jones]

Originally Posted by Daniel Epstein

It does sound like the people who can hear the signal are monitoring in Stereo and the people who can't hear the signal are monitoring in Mono. If she edits the piece in stereo and monitors in stereo she wouldn't hear the problem in the edit. This usually occurs when one source is recorded to two tracks but the tracks are out of phase and cancel rather than add. She should be able to fix it in edit. Use one track centered rather than two tracks left right

Before I let this thread fall too far into the past, I want to take a moment to thank everyone for their very valuable input. A number of responses I think touched on some very good points to consider, which I then subsequently explored with my friend who was experiencing the anomaly.

I think this last post from Daniel probably hit the nail on the head, and after all the other factors have been discussed, explored, and otherwise tested, it sounds like the most logical explanation to me as well. I didn't personally troubleshoot her gear and workflow since we are in different towns and our exchanges were by phone and email, but I definitely picked up that despite her 14 years working with video editing, her technical proficiency with Final Cut is not very strong and much of what I suggested to her (regarding sequence settings and export options) she claimed were somewhat beyond her understanding. Basically, it is an unfortunate situation of not having enough technical proficiency to back up the skills being sold to the client - but that's for another post.

After determining that neither the camera or the lav mic were contributing to the problem, it pretty much boils down to the settings being used in Final Cut.

I haven't heard back in a while as to whether or not she has gotten it working properly now, and don't know if she's had any luck with the settings I suggested she double-check in Final Cut, but since all has been quiet, I am assuming she's up and running again with properly functioning DVDs, and I am pretty sure that her audio settings were most likely at fault.

Thanks again, folks. I really appreciate it very much.

-Jon