Is this an audio dropout?

slacy wrote on 5/16/2005, 12:12 PM
In my last two shoots, I've noticed sporadic cases of "clicking" sounds in my captured material. I wore headphones during the shoot, so I'm confident there were no abnormalities at the time of shooting. When I went back and examined the source tape, I noticed the audio volume disappears for about a second at each point where the clicking sound appeared in my captured video.

Here's the sample file:

http://www.zagworks.com/client/sample.wm

So here's my question: is this a classic audio dropout? And if so, what could be causing it to occur and how can I remedy this in future shoots? I use a Sony VX2000. Is this the sign of bad tape stock, or head wear, or something else? I recently used the Panasonic head cleaner, for whatever that's worth.

Comments

Gonzoman wrote on 5/16/2005, 12:17 PM
Yikes - that's bad. Hope somebody here can help you with that.....
slacy wrote on 5/16/2005, 12:21 PM
Yeah, that audio is trashed beyond repair. I just want to avoid a reprise in my next shoot. :)
Spot|DSE wrote on 5/16/2005, 12:23 PM
sounds like a wireless or cable issue, not a digital dropout issue. Any additional specifics on your shoot gear?
slacy wrote on 5/16/2005, 12:24 PM
The frustrating thing is you can't detect the problem until you're back in the office. Pretty much any other major sound problem can be discerned and evaluated on the spot.
slacy wrote on 5/16/2005, 12:25 PM
I'm using a Lectrosonics wireless lav going into a Beachtek DXA8. I'd considered the possibility of a wireless problem, but wouldn't I hear that through the 'phones?
slacy wrote on 5/16/2005, 12:39 PM
Also, the "clicking" sound only appears in the captured material, which leads me to believe Scenalyzer is struggling to interpret the volume dropoffs. If the clicking were on the source tape, a cable problem would be my first suspect. But for a quick volume dropout, hmmm, I'm just not sure what to think.
RalphM wrote on 5/16/2005, 3:00 PM
The clicks sound more like a cable, etc, but the audio definitely dissappears as well.

To help isolate this, try capturing the audio from the analog outputs of the VX2000 into your sound card and see if the clicks are still there. If the clicks are there, I'd try bypassing the Beachtek to see what happens.

It's possible that the dropouts are from a high level pulse getting into the VX2K and causing the amps to clamp momentarily.

RalphM
farss wrote on 5/16/2005, 3:42 PM
It doesn't sound like a digital dropout, they normally have a high frequency zing to them. Also if it's a head/tape problem you'll most likely find a few twinkles in the video as well.

Really does sound like something in analogue land, the thump that goes with it kind of gives it away.

When monitoring audio on a shoot get sensitive cans, I use really cheap Behringers as they're the only ones I've found that'll give me enough sound level with Sony cameras to actually hear what's going to tape rather than the ambient sound. Then I press them hard to my ears and CLOSE MY EYES!

All that aside, it really sounds like a loose connection, the minipin plugs are a real worry. Test the rig at home, if you cannot repro the problem after wiggling every cable, plug and socket then it could just maybe be a RF problem. That looks like a factory, maybe they have something else generating RF, if that's the case try plugging the lapel mic straight into the camera using an extension lead.
Bob.
slacy wrote on 5/16/2005, 4:23 PM
Thanks for the help, guys. I'll definitely try all those things. But I'm still curious as to why the tape shows a volume dropout, and the captured media shows a click. Can anyone explain that?
farss wrote on 5/16/2005, 4:59 PM
Well if it is a genuine tape dropout then that can cause things to get muddled up. The audio on a DV tape isn't on a separate track, it's blocks of data muxed in with blocks of video. If bits of that data are missing you can see how things can get nasty for a few milliseconds.
Apart from that if you loose a bit of audio data you can get a very serious click as the value of the signal flies up/down in level, that's why Vegas puts small fades on cut audio.
Zoom right in on the audio, down to the sample level almost. If the waveform has a break in it it's most likely something that's gone wrong in the digital domain.

Bob.
Bob.
slacy wrote on 5/16/2005, 5:12 PM
Not sure what to make of it, but here it is:

http://www.zagworks.com/soundwave.jpg

ibliss wrote on 5/16/2005, 5:19 PM
It's a digital thing for sure - zoom in to a problem area and see the way the line deviates to form a square pattern. Couldn't tell you if it was a problem in record or capture though.

The good news is that you can fix it to a degree - which is to say you can eliminate the clicks, but you'll still have a slight audio drop out. Either use the left channel audio only, which is perfect, or open it in Soundforge and repair the clicks. You can draw them out manually, copyt the waveform from the left to right channel in the appropriate places.

If you have soundforge 8 the is an option in the tools menu called 'restoration' that will get rid of all of those clicks in one hit.

Not that you shouldn't try and prevent the problem in future... :)
ibliss wrote on 5/16/2005, 5:28 PM
Oh, and within Vegas you can use the Vinyl Restoration plugin (if you have it) in real time on the offending track.
slacy wrote on 5/16/2005, 5:29 PM
Thanks, Ibliss. I hadn't noticed the differences in the channels. Problem is, I switched to "left only" and there are actual dropouts on that side. So there are clicks in the right channel, dropouts on the left. Interestingly, the clicks and dropouts don't appear to be perfectly synchronized.

Things keep getting curiouser and curiouser.