Audacity Forum

I've been using Audacity for a while to record audio for Let' Play style videos and something has been happening recently that has been real weird. So before I was using Audacity 1.3 Beta Unicode to record audio at 44100 Hz on my laptop while I recorded video. Then I would export it as an mp3, sync it up in editing and everything would be fine.

Now I have a new, much better computer where I do all my recording and editing. So I installed Audacity 2.0.2 and installed the same video recording program. I recorded a 20 minute video and audio at 441 at the same time, like I did before. I exported the audio as an mp3, like I did before. I go to sync it up in post and the audio is about 10 seconds longer than the video. And I don't mean because of different recording start times. I sync the audio at the beginning the way I always do, then I go to the end of the video to trim some of the excess video and audio. The video stops, but the audio I recorded keeps going like I was still playing the game.

So now what I have to do is export the audio as an mp3 at 441, bring that mp3 into Audacity, then export it again at 48. It's really tedious and may also be starting to fail me, too. Does anyone know what is going on with my Audacity and why the audio is lagging so much?

DeadMan wrote:I recorded a 20 minute video and audio at 441 at the same time, like I did before. I exported the audio as an mp3, like I did before. I go to sync it up in post and the audio is about 10 seconds longer than the video.

MP3 is a "lossy" format that will reduce the sound quality so I'm wondering why you don't keep the audio in a high quality lossless format such as WAV until you have added it back to the video.

The audio is running 10 seconds slow over a duration of 20 minutes?
That's about 0.8 % slow.
What sound card are you using? Is it the same one as you used with your other computer, or is it just the on-board sound card included with the computer?
Audacity does not have its own "timing signal", it just accepts the audio data from the sound card and assumes that if the sound card says that it is 44100 samples per second, then it really is 44100 samples per second. If the sound card is running a little fast or a little slow, then the recording will not be quite the right length. If your previous sound card kept in exact time with your video camera, without being a calibrated or synchronised system. then you were extremely lucky. Drifting a little is not unusual for on-board sound cards.

You can use the "Change Speed" effect in Audacity to adjust the speed, or your video editing software may have that feature.

You know television doesn't run at 44.1, right? That's Music CD sampling. Television runs at 48. What's that, 91%? 9% error? Try a long capture and produce the work at 48000 sampling instead of 44100 and skip the MP3 step completely. Any video editing software should be able to handle very high quality 48000, 16-bit Stereo WAV files.

When I produce voice work for the Avid editors, that's what I hand them.

The worst error I expect by doing everything wrong and crossing the video and film rate barrier (in the US) by accident is about one frame per minute. That's about 0.6 seconds off. You should be able to hit it much better than that.

Koz

DeadMan wrote:.. I go to sync it up in post and the audio is about 10 seconds longer than the video ... The video stops, but the audio I recorded keeps going like I was still playing the game ...
Does anyone know what is going on with my Audacity and why the audio is lagging so much?

Running your game, and the screen-recorder, and Audacity simultaneously may be pushing your CPU beyond its maximum ability, causing recordings to drop (miss) a few samples now and again (skipping). The time difference caused by these tiny missing bits accumulates, causing tracks to become increasingly out of sync.

You could try setting a lower frame-rate for the screen-capture software, (so it does not tax the CPU quite as much). You should also switch off all unnecessary software, e.g. disconnect from internet whilst recording.

http://manual.audacityteam.org/man/FAQ: ... ting#skips