Audio Dropouts

craftech wrote on 1/26/2005, 6:31 PM

I guess if I had to pick one unaddressed problem with Vegas it would be a toss up between Blank frames, flash frames, and audio flatlines that occur during VidCap. In protest I refused to buy Vegas 5 as we have discussed before. The only reason I mentioned it again was that it comes up in other forums on the web. Example.....audio flatlines:

"The tapes, all filmed with the same camera (VX2k) had the same audio
dropouts, a flat line lasting either one or two exact frames. If I
recaptured the tape again using Vegas' VidCap capture software, the
dropouts were always in the exact same frames. Surprisingly the video
was perfect, as was the audio if played direct from the camcorder
audio out sockets. If I made a clone copy of the tape connecting by
firewire to a Sony TRV950, the resulting tape had the exact same
dropouts, whichever machine was used for capture.

I was able to complete the project by re-capturing the audio via
analogue - not ideal, but I had to get the project done... I
contacted SoundForge/Sony, who really had nothing to offer. They said
they had encountered it once before, and were then unable to explain
it. They were clearly not prepared to investigate further on what
they said was a very rare problem, even though I offered to send them
my precious session tape.

So I tried recapturing the tapes using a copy of Cinestream which I
used to use before Vegas. The tapes captured flawlessly via firewire,
with perfect audio. The same was true if I used Scenalyzer. So I
conclude that there is a bug/problem within VidCap, which strikes
occasionally. At least if feels nice that I don't appear to be alone!"

I don't need bells and whistles, just a reliable editor.

John

Comments

farss wrote on 1/26/2005, 8:01 PM

I've similar problems and not just with audio, video as well. Didn't get much sense from this forum but the Sony DV forum at Cow had a lot of good advice. The gurus over there said pretty much what you're saying.
Sometimes coping via 1394 to another deck will clear the problem, sometimes you need to capture analogue. No one could offer a precise explaination of just WHY these processes would work when a NLE couldn't get the same data via the 1394 connection.
I suspect it maybe a timing issue, just when the VCR can send the data packets may have some bearing on how well the PC can grab it. Certainly I doubt this is a Vegas specific issue.
Not trying to find excuses but I've had in happen where pass 1,2 & 3 were the same and pass 4 came good. Now if I was trying that with different capture software what do you think I'd conclude?
If you ever want to really see how marginal DV25 is, run a DB tape through a DVW 500 and watch the error level indicators, listen to the servos trying to keep it all together, makes me wonder how we don't have more problems with DV25 if that's what it takes to get 99.99999% reliable video.
Bob.

craftech wrote on 1/26/2005, 8:30 PM

I don't know if I made it clear that I copied and pasted someone else's post from a Yahoo forum who was experiencing this problem only when using Vegas for capture. He was not alone in that experience.

John

farss wrote on 1/26/2005, 8:54 PM

No, that bit wasn't clear!
Obviously it's not impossible that there is some weird gremlin in Vegas's VidCap utility. It's just that i see dropouts so regularly on DV tape and we get so many people coming to us with problems far worse than just the odd dropout that I think it'd be pretty hard to sort the problem from the 'noise'.
Everytime I've captured a tape that has had 1 frame audio dropouts when I go back and look frame by frame I'll find also one very tiny dropout in the vision as well.
Bob.

scifly2 wrote on 1/27/2005, 9:46 AM

was the tape new or previously used? Just curious. I have had problems with a JVC giving eroneous "condensation, operation paused" warnings and would kick the tape out. I later used that same tape and it had gliches in it that messed up the next project. I realize that souds off the wall, but I wonder if starts and stops in the time code of an earlier recording can "show thru" and trip up some captures. OK - just a thought, so go easy on me guys.

craftech wrote on 1/27/2005, 5:09 PM

The problem is random and is not on the original tape. The problem lies with Vegas VidCap. Sometimes it goes away of you recapture several times. There IS NO associated video glitch that is in synch with the dropouts. Do a search on audio dropouts and flatlines and you will see how often it can occur.

John

PeterWright wrote on 1/27/2005, 8:23 PM

I had this problem (audio flats + video glitches) when I bought a 2nd Camera to use as a capture device (my 3CCD Mini DV camera was pre-firewire).

I eventually traced it to playback from that camera, and my only solution was to buy a DV deck, which has been fine ever since, so in my case it was hardware, not Vegas.

farss wrote on 1/27/2005, 8:57 PM

I really have to agree with what Peter is saying, I've struck this a few times and there are definate video dropouts, sometimes they're only a few pixels in one frame so you have to look damn hard to see them. Of course if the data on the tape is marginal then repeating the exercise may well get it back OK.
Data recorded onto a magnetic medium isn't truly "1"s and "0", it's still analogue, if it's over a certain level it's a "1" else it's a "0" (yeah, I know it's way, way more complicated than that and I realise the B/H curve of digital tape makes it harder for this to happen). So sometimes you get lucky and the slightest shift in any of a number of things mean you finally get your "1"s as "1"s and "0"s as "0"s and you're away.
Bob.

Grazie wrote on 1/27/2005, 9:39 PM

THANK YOU BOB!

At last somebody has truly vindicated and supported my own "thoughts" on this now - simply with these 2 statements:-

1/- "Data recorded onto a magnetic medium isn't truly "1"s and "0", it's still analogue, . . "

2/- "So sometimes you get lucky and the slightest shift in any of a number of things mean you finally get your "1"s as "1"s and "0"s as "0"s and you're away. "

Bob, some basic physics does go a loooong way . . excellent!

. .and also, does error correction always work IN our favour? Decks do have error correction? Yes/no?

Thanks Bob!

Grazie

Rosebud wrote on 1/27/2005, 11:53 PM

John,
I had same problem with Vegas and Premiere.
I confirm i never had any drop with Scenalizer.

farss wrote on 1/28/2005, 12:08 AM

I'm not certain how much error correction there is in DV25, I suspect not much as it was designed a fair while ago when silicon wasn't that fast. Writing ECC means buffering the data, calculating the code and writing it to the tape and the reverse process happening on playback, and remember this has to happen in RT. Audio CDs use a fairly complex system of error correction and minimization and even that's pretty dated by todays standards, you get much more reliability saving audio as data files than you do burning to as a CDA (assuming you used the same media!).

Error correction works in our favor but it does have a cost, just look at the cost of ECC RAM and it's oftenly slower. The one problem with having lots of error correction is when it can no longer correct things fall apart very badly, thats why a lot of the pro stuff actually indicates the current level of error correction, when the number get high you know it's time to dub the content to a new tape or replace the disk or the RAM.
Bob.