Hello,
I do not have experience with Audacity so maybe I’m doing something wrong.
In Audacity, I wanted to clean up the audio file from the noise and then join it with the video in Camtasia.
In Audacity I loaded mp3 library: libmp3lame-win-3.99.3
After cleaning the noise (based on the fragment with noise) I export the audio file as mp3. Next I import such a file to Clip Bin in Camtasia and put it on Track 1. When I press Play, I hear that voice is backing away from the graph I see. I hear the voice at the point marked on the screen shot as “1” and the voice chart starts at point “2”. In the original, not denoised audio, both the voice and the voice chart started at point “2”. I do not know what’s going on. Even if I do nothing in Audacity (even denoising) and just export the file as mp3, it is the same. It makes it difficult for me to match the audio with video in Camtasia.
This does not happen when I save as mp3 in Adobe Audtion.
I already many times joined audio with wideo in Camtasia, but then those audio files were not processed by Audacity.
Thank you in advance for your help, what I am doing wrong 
Don’t use mp3 , use wav, then there shouldn’t be any synchronization problems.
( making mp3 unavoidably adds a fraction of a second silence at the start which can be enough to ruin lip-sync )
Me too dont have much experience with audacity and was facing same issue but as told in previous reply i use Wav instead of mp3 and gradually solved the problem.