Noise reduction changing timing on audio

I record videos for youtube. Since i am just starting, i do not have the luxury of any super fancy mic or sound proof. I use the Blue Snowball Ice microphone, which is decent for the price, but can record a lot if background “noise”. So, what i usually do is extract just the audio from the video with quicktime, then use audacity on the audio with the “noise reduction” effect. Then i use Imovie (obviously meaning I’m a mac user) to put the new audio over the video and mute the original audio. In theory should work perfect.

Heres my problem. For some reason the new audio is someone always off in timing. It is the same length of the video, but no matter where i put the audio within 2 minutes the audio stops syncing, almost as if it has been sped up by like… 1 second. I can not seem to figure out how or why this is happening. The only editing being done to the audio is noise reduction. Is there a fix for this? Is there something I’m missing? This happens constantly with every video and I end up having to spend ALOT of tedious time aligning the audio by having to split it up when it begins to un sync. I feel like it should be as simple as just putting the audio with the video, since it should be the same, minus the noise. What is going on? I am very new to editing and don’t have money to buy any better programs. Any advice, help, or even just an explanation as to why this is happening would be great!

I got fuzzy ideas.

Video generally runs at 48000 sample rate not 44100. You might try recording a piece at that rate, or converting to that rate when you get a finished clip and see if that helps (change the number lower left).

A clip playing too fast usually means it was recorded too slow. If the recording computer can’t keep up with the microphone, it might drop tiny pieces of the performance here and there. Not enough to hear, but the show will play fast. Like it may get to the 3 minutes mark before 3 real minutes have gone by. But you said the sound file was exactly the same length as the video.

There is one really out there possibility.
We used to have constant sync problems in the US because the video framerate was not 30. It was NTSC Color framerate of 29.94. They did that to make broadcast color look better. It was just far enough off so you notice a sync problem about a minute in. A lot like what’s happening to you, although I don’t really think it’s the same thing.

Your Mac may not be fast enough to play that many QuickTime layers. Do you have a Solid State Drive and lots of memory? Has this ever worked? Does it work better if you restart the Mac and only launch QuickTime. Mac people have a habit of leaving tons of applications alive but napping instead of closed.

Desperation Move. Can you make it worse?


If you have 1 second difference, how long is the video in total?

1 sec could be “normal”, if it’s on a 30 min. video.

That’s why professionals use gear with external an clock input, that will record a time track. When they bring together audio and video from different sources.

If there’s no time track, manually aligning is all you can do. No expensive software to fix that, cause it can’t be automagically fixed.

How long is the video in question?

If you have a stable error, you might try Effect > Change Speed before you push the new sound into the show. Keep messing with it until you get one new track to sync down the whole show. That one speed correction may then work on all the new segments.

If it doesn’t, or it works at the two ends but not in the middle, then you have an unstable error and minute by minute correction may be the only solution.


Suppose as a test you export the audio without Noise Reduction. I am betting the audio would still be desynchronised. As far as I know< Noise Reduction is sample accurate, so does not change the length of the processed audio.


Does the original video play with sound and video in-sync?

faced the same issue and the above suggestion fixed the problem, thanks.