I am rather new to Audacity and am currently editing a Podcast. I am having the following issue:
The microphone track I recorded with Audacity contained a - probably normal - background noise. I silenced that background noise while an interview partner was speaking on another track.
After I’ve done so, there is a crack noise every time the silence ends or begins. Removing that crack (vertical line) does not help, as another one is created instantly. I noticed that the audio on that channel is below the 0.0 middle line - not sure why.
You’ve go a [u]DC offset[/u] which is caused by a problem with your soundcard or interface. The Normalize effect has a DC offset removal option, or since DC is “zero Hz” it can be removed with a high-pass filter.
That’s called “DC offset”. It’s a (common) hardware fault.
Ideally it should be fixed by using better hardware, but if that’s not an option then it can be corrected after recording but before editing.
If it’s too late to undo your edits and you don’t have a backup of the pre-edited audio, then to fix the problem you will need to carefully select each part that has DC offset (use “Zoom” as necessary to precisely select) and correct the DC offset as described in the first link.