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Old June 14th, 2009, 10:30 AM   #1
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Applying an offset to sync Zoom H4 with Camera

I tried a number of audio editing software to change the duration but only Adobe Sound Booth did it correctly, unfortunately it takes 2 half hours to change an hour of audio. What do you use to apply the offset? I found most software can’t handle small time changes, they either round off the percent, cut off after the second decimal place, yielding the wrong time.

List of the software I tried:

PeakDV, Cubase, Sound Forge, Audacity - wrong length
Soundtrack Pro – can only change length by time not by %. I don't want to calculate the time offset for every clip.
Sound Booth – works but takes a long time, but I'm thankful because without it I wouldn't know what to do.

I read the H4N, is more accurate, but would you still need to sync it for 1 hr recordings? My H4 was pretty off compared to my Sony Z1U, 12 frames an hour or 40ms.
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Old June 14th, 2009, 11:42 AM   #2
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Sony Vegas. Offset and/or time-stretch/compress to the sample level. No render time needed.
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Old June 14th, 2009, 12:19 PM   #3
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Originally Posted by Rick Reineke View Post
Sony Vegas. Offset and/or time-stretch/compress to the sample level. No render time needed.
Unfortunately, I'm a Final Cut Pro user. It worked for smaller clips but gave me a "trim" error when I tried it on an hour clip. Well for now I'll stick with Sound Booth.
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Old June 14th, 2009, 05:57 PM   #4
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Sound Forge can do this as well, not as easy as Vegas though.
Only the "pro" full version of Sound Forge supports this process as I recall.

Bias Peak probably has the time stretch/compress tool. You may want to look into that.
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Old June 14th, 2009, 09:35 PM   #5
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Originally Posted by Rick Reineke View Post
Sound Forge can do this as well, not as easy as Vegas though.
Only the "pro" full version of Sound Forge supports this process as I recall.

Bias Peak probably has the time stretch/compress tool. You may want to look into that.
Like I said I tried both and they don't yield the correct time length.
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Old June 15th, 2009, 05:45 AM   #6
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I hate to sound snarkey but it's always better to avoid the problem in the first place than it is to fix it later. A better approach is not to look for software to fix a problem caused by the hardware but to use hardware that avoids the problem. To do that, the camera and the recorder sample clock must share a common timebase. Get rid of the H4 and use a recorder such as the Tascam HD-P2 that syncs to video blackburst from the camera and the problem goes away.
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Old June 15th, 2009, 08:05 AM   #7
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Pete -

I hear you brother - I went through the same thing.

Audacity works for me. I load the audio, select it all and then select Effect / Change Tempo with a Percent Change of 0.009. It doesn't take long at all and the audio syncs up perfectly.

I had tried Soundbooth as well, but had the same experience as you did - slow as molasses in winter.

- Rick
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Old June 15th, 2009, 09:44 AM   #8
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Pete -

I hear you brother - I went through the same thing.

Audacity works for me. I load the audio, select it all and then select Effect / Change Tempo with a Percent Change of 0.009. It doesn't take long at all and the audio syncs up perfectly.

I had tried Soundbooth as well, but had the same experience as you did - slow as molasses in winter.

- Rick
I got Audacity to work but my math is a little rusty so I'm not sure how Audacity derives its tempo percentage.

After an hour Zoom H4 is 12 frames slower than the camera
1 frame = .0334 seconds * 12 = .4 seconds
1 hr = 3,600 sec / 3,600.4 sec = 99.988854 % (decrease length) or 100.01111% (speed increase)

Either of theses percents don't work in Audacity. If I enter desired seconds in the Tempo dialog box, it gives me 0.667 as the correct % to use. How is it calculating it? What is that a percent of?

Now that I know the setting I can write it down. I'm going to listen for any audible quality difference between Audacity and Sound Booth. If none I'll save myself the time. Thx
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Old June 15th, 2009, 04:06 PM   #9
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On my last project I just changed the speed of the audio clips to 99.9% on the FCP timeline and it worked fine, although I wasn't running clips more than about 10 minutes long. Just got the H4n today and planning to use it on a shoot tomorrow so I'll let you know if it still needs retiming.
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Old June 15th, 2009, 06:01 PM   #10
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On my last project I just changed the speed of the audio clips to 99.9% on the FCP timeline and it worked fine, although I wasn't running clips more than about 10 minutes long. Just got the H4n today and planning to use it on a shoot tomorrow so I'll let you know if it still needs retiming.
I'm using it only for continuous recordings of live events, so the percent has to be very precise otherwise it won't be in sync.

I really want to get the H4N because there are so many improvements over the H4 but for my purposes I couldn't justify the the extra $150.
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Old June 15th, 2009, 06:45 PM   #11
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Pete -

I screwed around endlessly with Audacity and Soundbooth before coming up with the .009 number. I don't remember exactly how I calculated the number, though, it was a while ago.

My clips are quite long - most of them are over an hour - and the fixed audio stays synced thoughout. Hope it works for you!

- Rick

P.S. My video is from a Canon HV20.
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Old June 16th, 2009, 07:35 AM   #12
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I used Audacity and this procedure:
My Video Problems :: View topic - Synchronise external and camera audio tracks.
to calculate the offset, which of course will almost certainly be different for every camera/ recorder combination.

Don't forget that even if the recorder sample rate is absolutely spot on, and it is the camera 'clock' that is slightly off, then you still have to correct the audio track. The 'wrong' camera track is the one that is in sync with the video, and has to be the master.
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