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out of sync, 44.1 to 48KHz

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Andreas Dalsgaard
out of sync, 44.1 to 48KHz
on May 18, 2011 at 1:19:29 pm

Hello CC,

I have a video&sound recording that was made in 48khz. The camera used was a panasonic AG-AF100. I want to sync this recording with a soundrecording made on H4 Zoom HD in 44.1khz. When I sync the two recordings they move progressively out of sync. About two seconds in a 30 min recording.

I assume that the problem is the difference in khz, but is this true?

How do I convert the 44.1khz recording into something that will be in sync with the 48khz recording. It is not done by simply converting the 44.1khz into a 48khz.

Sincerely,
Andreas Dalsgaard


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Mark Spano
Re: out of sync, 44.1 to 48KHz
on May 18, 2011 at 2:26:15 pm

[Andreas Dalsgaard] "they move progressively out of sync. About two seconds in a 30 min recording."

Yep - I've seen that before in standalone non-lockable audio recorders like the Zoom. It's recording at a slightly different speed than your camera. The audio from the Zoom is likely more accurate to actual time, but since picture rules, you need to sync that audio to the camera audio in order to get video/audio sync. The problem is not the sampling rate mismatch. A second should always be a second, right? However, if one of these recorders is slightly faster than the other, then playback at its recorded sampling rate will be out of sync with reality.

The only solution I've been able to use in this scenario (which does come up often) is to use a professional audio workstation software with a really good time compression/expansion plugin. Pro Tools has a good one, and Avid MC uses the same algorithm. The process is relatively simple. Place the audio and video on the timeline so that they are in sync at the start of the program. Then navigate to the end and find something visual that you can reference in the audio. Figure out the difference between the timecode where it happens in video and the timecode where it happens in audio. Apply the time compression/expansion plugin to the audio and add or subtract the found difference to the total duration. Process/render the plugin and they should now be in sync for the entire program.

The more ideal way to achieve this is to figure out the speed difference and vari-speed the audio to match. Unfortunately, tools to accomplish this are seldom found and a lot of times more hassle than just time compressing/expanding. Those plugins are good, and for a minor change like this usually needs, can sound pretty transparent.



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Andreas Dalsgaard
Re: out of sync, 44.1 to 48KHz
on May 18, 2011 at 3:19:03 pm

Thanks. Clear answer to my question, although the facts you offer are annoying. Gotta go. Gotta compress a lot of files...:-)


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Elliott Klein
Re: out of sync, 44.1 to 48KHz
on May 19, 2011 at 7:38:02 am

i to have found that problem using the zoom H4 where it slips out of sync about 2 frames per 30 mins, has to do with the internal clock in the h4 not being the same speed as the camera

they managed to fix that problem with the zoom H4n's and i have not had any sync issues so far with them

what Mark said is how i have fixed the problem in the past


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