Audio Sync Drift

Can slow or mis-behaving SAN cause audio sync drift from an embedded SDI source? I'm trying to track down the issue I'm having with the FCP system.

Config:

Intel Mac Pro 2x3GHz
8GB RAM
Mac OS 10.4.11

Storage:
6TB fibre connected SAN (MetaSAN controlled)

Deck:
HDCam deck to Kona 3 via SDI with embedded audio

Sequence/Format:
ProRes 1080i

I've dig'd twice. Once after trashing FCP preferences in case there was something wonky there. Digitized clip drifts both in FCP and in Quicktime.

Am currently digitizing to a local drive to rule out the SAN, but I thought I'd ask what are the most common reasons for audio drift from an SDI injested clip. I suspect the SAN because it's old, and I've had strange issues with it in the past (clips disappearing/going corrupted, spontaneously unmounting). The boss has purchased new, but is dragging feet in upgrading because the dept. might be moving locations, so I'm stuck with it for now.

Like I said, I suspect the drives, but maybe the Kona could be the problem? If this current digitize doesn't work, I plan to remove the Kona from the configuration if only to see if the clips digitized are REALLY out of sync and not just being played out of sync by the card.

Thoughts?

Andy

All the suspects you named are possible (capture card, the SAN...) in my experience. Have you tried just copying one of those clips to a local drive before checking again on QuickTime Player? I think you should make sure it's not just a playback drift before you recapture everything.


www.derekmok.com

How many embedded audio tracks?

It's unlikely the clips are merely being played out of sync as the resulting QT from a capture of embedded audio isn't any different from one with conventional audio. The QT will still have separate tracks for each audio track.

If possible I would try an audio only capture on a clip and then a video only capture of the same tc and see if they stay in sync once you line them up in FCP. This might help in tracking down the problem.

Another thing to try, if you have the hardware to do it, is to demux the audio from the SDI before it gets to the Kona. There are boxes that can be rented to do this.

ak
Sleeplings, AWAKE!

Thanks for the replies. Here's some more info:

The length of the capture is roughly 16 minutes. There are 2 channels of audio (simple LR stereo pair). I have no other means of getting the video into FCP because I only have an HDCam master. And since I don't have another capture card available, I can't rule out the Kona until I've ruled out everything else. The audio drifts ahead of the video. By the end of the 16 minutes, the audio is about 10 frames or so ahead of the video.

Here's what has NOT worked:

Restarting
Trashing Preferences
Moving a digitized clip from the SAN to Local Drive
Digitizing to Local Drive vs SAN
Digitizing in another codec (uncompressed vs ProRes)

Here's what has worked:

Breaking clip up into small 2-3 minute clips (expected)

I'm currently trying Andrew's idea of splitting up the audio. I'm pulling in video via SDI, and audio via AES. Not exactly demuxing, but a useful test. I still have yet to try the video only, audio only captures, but as the capture is 16 minutes each time I do it, I thought I'd try this first.

The other remote possibility could be a rack problem. I can still try to digitize by connecting the HDCam directly into the Kona's breakout box. Of course, if the breakout box is the problem...

Andy

More info:

Splitting the audio and video did NOT work. When clips are married in the timeline, the same audio drift is apparent.

I beginning to really believe that this is a Kona issue. I watched the throughput to the monitor from the Kona and sync was perfect the entire way through the digitize. But when I watched the finished clip, it was out of sync.

I feel I've ruled out the rack, the deck, and the drives.

Gonna call AJA tomorrow.

Andy