Audio-Video Synch
 

I may be missing something obvious, but using a 25' xlr cable connecting an at835b mic to a Beachtek adaptor to a vx2000 mic input, I noticed my audio is slightly out of sync with my video.

Dumb Q#1: Does the length of xlr cable matter? (I know the conversion of sound to electrical impulses (i.e. speed of sound issue, etc) occurs at the mic, and the mic was close to the audio source, so I assume the answer should be no.)

Dumb Q#2: Does use of the adaptor, which i assume, other than providing phantom, is a passive device do anything? Couldn't be it in my mind.

Dumb Q#3: I've read that the minidv standard doesn't 'lock' the audio to the video channel. What does that mean and is it relevant? Is the vx2000 at issue?

I've read posts re a similar problem with the xl-1 but that was in longer-than-7min recordings. This occurs in shorter ones, when brought into Premiere 6.01 through a DV500. Any ideas? Thanks

1) a 25 ft XLR cable will NOT put sound out of sync..

2) XLR box will not put sound out of sync

3) the mini dv "unlocked audio " specs call for it to be within 1/3 of a frame ..therefore you will NOT notice the drift ...

when you say OUT of SYNC = where do you see this out of sync? when you view the tape ? or when you view it after digitizing ?
it after digitizing then looked into you software/hardware ...

these hand size dv camera's do not run audio at a perfect 48K ..there were problems with this 2 years ago BUT most vendors have ways to correct it... i don't use dv 500 but perhaps somewhere in premiere there is a selction of camera 's ?? also did the premiere 6 come with the dv 500 ? if not then that could be the problem = as it would be a stand alone version and not the dv 500 version

i digitize whole 60 min tapes with out any sync problem.

Thanks for the reply! I see it upon playback after capture. The DV500 came with Premiere, and I'm assuming there must be a problem after capture that's causing it. I'll test by listening to playback from the camera itself.

A couple of quick questions...
1.... did you drop any frames during capture?
2.... does the audio sync problem get worse as the clip plays?

no dropped frames, but i need to check on whether it gets worse over time -- if so, i guess that would indicate a frame rate mismatch in software?

hmmm....a sync problem that gets more and more out of sync would probably be frame drops somewhere along the line....or possibly frame adds...which would be unlikely.

you might check to make sure you have the newest drivers for the DV 500 .. if yes ?? - you might post on a dv 500 board

Whenever I've had this problem, it has always come down to discrepancies between audio rates, i.e. original material shot at 48K and digitizing/editing/compression software set for something different, such as 32K. My suggestion would be to confirm the rate at which it was shot versus the Premiere audio prefs for digitizing and sequences. (I use FCP so don't know exactly where to look in Premiere :) )

There is another way this can happen. Depends on how your editing setup works.

Basically, if you are watching the video on the computer monitor and the speakers are driven from an outboard device like, say, a VCR that is getting a feed via the FireWire port, you will most likely hear/see a sound sync problem. If you listen to the computer-driven speakers or watch a monitor connected to the VCR everything will be in sync.

What happens when you view the tape directly in your camcorder and listen to the sound? Or if you make a tape from the DV500, is the sound/picture in sync?

Wow, you seem to have called it Mike. I'm still trying to figure out exactly what's going on, but I don't think there's a sync problem when listening from the camera. I am running the sound out the RCA jacks of the DV500 patch box and then back in to my sound card (and then back out to my computer speakers). That's the recommended set up on Pinnacle's site!

Thanks so much everyone!

Madeline, you may not want to hear this but I must ask what you are doing your processing on? By that I mean, how fast is the PC and how much memory are your running. An X86 based PC does only one thing at a time (no matter what Bill Gates tried to tell you!) It sounds like your PC places a higher priority in getting the picture portion done first and the sound is of secondary importance giveing you an out of sync problem. This can be caused by a slow processor, no enough memory or a bunch of extra stuff going on in the background. Do you have a bunch of task bars on your computer? You know the bars that let you select programs without going into "Start", then "Programs", then clicking on the program name? If you have these things try shutting them off. They eat memory! What I am suggesting is for you to clean up your platform as much as possible and then see how that affects your problem. If it doesn't help, well at least you screen is clean!

Later!

Thanks Ottotune (whenever I see the name Otto all I can think about is Kevin Klein)....it turned out to be the circuitous route the audio was taking through my system. I'm running a dual Xeon 2.0 workstation with 1.5 Gig RAM, so I'm guessing the system was doing ok. Thanks again for the response!

OK, good deal! Sounds like you are up to speed in the processing area.

No, everyone knows that the speed of light is 186K miles per second... but the rest of the equation says 'in free space'. If you confine either light or electricity it goes somewhat slower. Electrically speaking, the average chunk of cable has a velocity factor of .66 so the speed of light is almost cut in half in a cable. If you get the very finest and best in cable you can raise that value to approx .75 of the speed of light.

Background: The moon is approx 1/4 second away at radar speed (the signal, whether electrical or light has to go there and come back, or make two trips, hence 'radar distance'). If you watch CNN and some of the reports out of the middle east you will see signal delays ov up to 4 seconds which at light speed is a tremendous delay. Each one of the conversions from electrical for transmission to light for fiber optics transmission takes a significant amount of time.

At one time I did some long mic lengths in the neighborhood of 1000 feet and greater and you can get into some interesting time delay problems. Different frequencies can propogate at different rates creating a really neat audio problem to solve!

Have fun!