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Experiencing Audio Drift in Vegas, unsure what's wrong

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Morgan Lewis
Experiencing Audio Drift in Vegas, unsure what's wrong
on Oct 5, 2014 at 3:28:35 am
Last Edited By Morgan Lewis on Oct 5, 2014 at 4:29:04 am

My cousin and I do Let's Plays from time to time, basically we play a videogame and chat, because there's two of us there our commentary track also has audio from the game, so I have to sync them up.. which is easy, but lately I've noticed there's something wrong.

I'm looking at a 1.5 hour recording here, I just synced the beginning so that someone talking in the videogame matches in both the game audio and our commentary audio, then out of curiousity I went to the end of the video.. and it's echoey. Moving the commentary 0.03 to the left brings it back in sync and naturally puts the beginning out of sync. It's only a little bit but it's very noticable.

What could be causing this? The game audio is fine, if that was out of sync it would be obviously notacble as lipsync and other factors would show something's wrong. My cousin's computer is more than powerful enough to handle our video and audio recordings.

I'm using Vegas Pro 10, we use an HD-PVR to record a m2ts file for the game footage and we use recordpad to record a .wav as 48000hz, 32bit.

Looking in project settings, audio can only be set to 24 'bit depth', is this the same as bitrate? Could this be what's causing the problem and changing my recording to 24 bit could be the answer?

If not I'm quite lost, and this is quite an annoying issue...


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Dave Osbun
Re: Experiencing Audio Drift in Vegas, unsure what's wrong
on Oct 5, 2014 at 4:33:53 am

I highly doubt that both of your recording programs record at the same exact clock 'speed'. This is why professionals that record audio from multiple devices use genlock.

Not sure what you can do except slice the secondary audio into separate 'slices' and move each section by a frame or two to sync them.

Dave


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Morgan Lewis
Re: Experiencing Audio Drift in Vegas, unsure what's wrong
on Oct 5, 2014 at 5:07:22 am

Well the thing is, I 'did' used to get perfect sync... maybe it's when I upgraded recordpad to a later version, perhaps it can't handle longer recordings as well. We switched because the recordpad we were using would only record in hour chunks for some reason.... now that I think about it our last perfectly synced project might have been using that.

Just so I learn something anyway, what's clock speed? Both the game's audio in the video and the game's audio as captured by our mic should both happen at the same time surely?


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Bob Peterson
Re: Experiencing Audio Drift in Vegas, unsure what's wrong
on Oct 5, 2014 at 9:38:24 pm

For a digital recorder, it is necessary to have a clock that tells the recorder when it should capture a sample of the audio. For example, if you are recording with a sampling rate of 48,000 samples per second, the clock tells the device when it is time to capture a sample. If two recorders are working, their clocks may be slightly out of synch and the audio from one device will begin to diverge from the audio on the other device when they are subsequently played back with a single clock used for both sources.


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Morgan Lewis
Re: Experiencing Audio Drift in Vegas, unsure what's wrong
on Oct 6, 2014 at 5:22:00 am
Last Edited By Morgan Lewis on Oct 6, 2014 at 5:35:19 am

Ah I see, so despite both being 48,000 it would be pure luck to get them perfect if using two different programs? I see.

So it's definitely the clock speed despite both being the same sample rate then... hmm, Is the clock speed always the same for devices? Would it be possible to find out what clock speed my HD-PVR is and tweak my audio program appropriately? Or am I just kind of doomed to re-syncing every 30-60 minutes?

I have some PC recording coming up soon that'll use one program to get both game and commentary (DXtory), it does them both at the same time... hopefully that means they'll both be fine? ^^


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John Rofrano
Re: Experiencing Audio Drift in Vegas, unsure what's wrong
on Oct 6, 2014 at 11:20:54 am

[Morgan Lewis] "Moving the commentary 0.03 to the left brings it back in sync and naturally puts the beginning out of sync. It's only a little bit but it's very noticable."
You can stretch the audio to match the video. You said that moving 0.03 to the left brings it back in sync. Instead of moving, Ctrl+Click and Drag the right edge of the audio 0.03 to the left and it will time-stretch the audio to be in sync with the video all the way through.

~jr

http://www.johnrofrano.com
http://www.vasst.com



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Morgan Lewis
Re: Experiencing Audio Drift in Vegas, unsure what's wrong
on Oct 6, 2014 at 11:45:44 am
Last Edited By Morgan Lewis on Oct 6, 2014 at 12:07:03 pm

For some reason stretching didn't occur to me (nor did I know how to do it)... I will test this later when I'm at my project computer. I usually zoom right in and use the numpad to do precise and small movements though, will ctrl-click-drag when zoomed in be accurate enough... is it possible to do this with the numpad controls at all?


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John Rofrano
Re: Experiencing Audio Drift in Vegas, unsure what's wrong
on Oct 6, 2014 at 11:44:14 pm

[Morgan Lewis] "will ctrl-click-drag when zoomed in be accurate enough... is it possible to do this with the numpad controls at all?"
You can actually open the properties once you've Ctrl+Dragged and type in the exact number that you want to time-stretch. This is extremely accurate.

~jr

http://www.johnrofrano.com
http://www.vasst.com



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Morgan Lewis
Re: Experiencing Audio Drift in Vegas, unsure what's wrong
on Oct 7, 2014 at 3:14:48 pm

Ah I see, the menu that has Classic and Elasque as the options? What should I be going for here? I know I'm only making a very minor stretch time-wise but I don't want to screw up my audio with pitch shifting.


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John Rofrano
Re: Experiencing Audio Drift in Vegas, unsure what's wrong
on Oct 7, 2014 at 8:25:10 pm

[Morgan Lewis] "I see, the menu that has Classic and Elasque as the options? What should I be going for here?"
You want élastique which is the default. Classic is the older technology that Sony used and Zplane élastique timestretching is the newer "much better" technology. You shouldn't even notice that it was time stretched.

~jr

http://www.johnrofrano.com
http://www.vasst.com



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