Will digital audio recorders stay in sync with DV video?

[Seatlanta]

Thanks, everyone, for your input.

As some of you suggested, I did a test with my Canon mini-DV camera and my Fostex MR-8 digital recorder.

I set up the camera and recorder next to one another and set them both to record. I created a sync signal by banging two film cans together a few times, then waited almost an hour and did it again near the end of the tape.

Here are the results:

With a long video take of 53 minutes, along with two versions of audio (DV tape and Fostex), the end-of-tape sync signals were off by 8 frames–barely more than 1/4 second.

A slight control-drag adjustment and everything lined up. And with normal-length takes, I probably won’t have to do any adjusting at all. This is good news for me because I now have a very accurate wild sound option.

And it’s a cinch to remove the compact flash card from the Fostex and dump the wave file into Vegas (or Sound Forge).

James (seatlanta)

[Dave Haynie]

Yeah, the accuracy of a digital recording is based on the accuracy of the clock. This is not usually a problem in modern gear, because plain old everyday cheap quartz clocks are usually at an accuracy of 50ppm, at worse 100ppm. Even 25ppm is possible on a limited budget — I use this kind of accuracy in 2.4GHz consumer radio gear I design. So that’s a worst case of something like 0.01% on the clock; 1% would be ridiculous, not much better than the L/R/C oscillators of the past.

With that said, you are talking about at least two of these clocks, totally unsynchronized, when recording with outboard gear. They will eventually walk away, you synced audio-on-video and the outboard recording, the real question isn’t “will they”, but “will they within the hour or so I’m hoping they stay in sync”.

I routinely use MiniDisc and direct-to-PC recording in the field. There’s usually no issue with sync loss, but it’s smart to have good sync points in the audio tracks anyway. If you have a clapboard — that’s what the “clap” is for. In a pinch, I’ve used a quick, high note on a harmonica. Naturally, some recordings offer ample opportunities. You never count on your ability to start them together; that’s also assuming the latencies in your controls are the same, and for that matter, that your video and audio devices are close by. I’ve shot events with a PC near the stage recording from mics, the camera in the back, and an MD recorder or two hidden in strategic locatings, and never had sync problems.

-Dave