Audio runs out of sync

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Audio runs out of sync

Permanent link to this post Posted by GreaperBeeper » Sat Feb 04, 2017 1:29 am

Hi, I am using audacity to record a podcast

We recorded through usb mics on seperate computers (both with audacity) and the files are in adacity, but ive noticed that they start synced together, but during the 1.5 hour clip they run out of sync, so much that theres a 5 second delay between the two of them.

I've tried changing the tempo, didnt work. any ideas or help?

Thanks
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Re: Audio runs out of sync

Permanent link to this post Posted by kozikowski » Sat Feb 04, 2017 2:43 am

I'm sure you noticed that given desirable recording environments at each location, this works far better than trying to capture Skype. It's also readily expandable to multiple performers.

It's not Tempo. It's actually Speed. So select one of the two performances, do the math to figure out how much longer or shorter it is than the goal and generate a percentage or ratio or any of the settings that Effect > Change Speed can work with. The cool part is once you figure it out, it's a constant and it doesn't matter how long the show is. When Aunt Fanny's show is downloaded, it's always going to be 0.3% slow. Simple compensation.

If that's not correct, then the recording system is faulty. One of the computers could be changing speed during the show. That will need to be fixed at the computer. There's no good, easy way to compensate for that.

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Re: Audio runs out of sync

Permanent link to this post Posted by kozikowski » Sat Feb 04, 2017 2:44 am

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Re: Audio runs out of sync

Permanent link to this post Posted by kozikowski » Sat Feb 04, 2017 3:39 am

If anybody changes a computer or recorder this will change and have to be recalculated.

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Re: Audio runs out of sync

Permanent link to this post Posted by DVDdoug » Sat Feb 04, 2017 5:35 am

We recorded through usb mics on seperate computers (both with audacity)
Each soundcard or USB mic, etc., has its own clock (oscillator). That's the clock that provides the sample rate (44.1kHz, etc.). No clock is perfect and over time they WILL drift apart. But, 5 seconds over 1.5 hours seems like a lot. Are these "cheap" USB mics or "studio style" microphones?
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Re: Audio runs out of sync

Permanent link to this post Posted by GreaperBeeper » Sat Feb 04, 2017 5:50 am

Theyre studio level, paid about 129 for mine and 95 for the other
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Re: Audio runs out of sync

Permanent link to this post Posted by steve » Sat Feb 04, 2017 11:01 am

GreaperBeeper wrote:Theyre studio level

If they are "professional studio level" then the solution is to link them to a common "word clock" (See: http://www.soundonsound.com/techniques/ ... ster-clock).

External clock synchronisation is generally only available for professional studio level sound cards, not consumer level or even "home studio" level. ($100 to $200 for an audio I/O device is really "home studio" level rather than professional level)
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Re: Audio runs out of sync

Permanent link to this post Posted by steve » Sat Feb 04, 2017 11:04 am

GreaperBeeper wrote:I've tried changing the tempo, didnt work.

Why not? What exactly "didn't work"?
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Re: Audio runs out of sync

Permanent link to this post Posted by kozikowski » Sat Feb 04, 2017 5:49 pm

Yeah. That should have done something, just maybe not sound very good. I expect Change Speed to sound perfect once you hit the correct compensation.

Post back if we lose you. We can take you through step by step.

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Re: Audio runs out of sync

Permanent link to this post Posted by steve » Mon Feb 06, 2017 11:02 am

kozikowski wrote:It's not Tempo. It's actually Speed.

To adjust the speed of one track so that it matches the speed of another, use the "Change Speed" effect. The "length" parameters are generally the most useful for this type of task. http://manual.audacityteam.org/man/change_speed.html
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