I record lecture notes, and they contain giant pauses filled with white noise. Is there some way I can get rid of those passages completely? Using Audacity, I can reduce the white noise (i.e. turn it into silence), but what I'd like to do is crop those bits out from the file so I don't have to play "hunt for the lecture".
Try this, assuming you can use a sufficiently recent (post 2007, unstable) version of audacity.
Summary of the suggestion, as requested by @slhck:
Obtain a version of Audacity later than version 1.3.3. The stable version of Audacity is from 2006, and does not contain the same functionality as the more recent preview releases.
Open the file you want to remove the whitespace from.
Go to Effect > Truncate Silence.
Set Min silence duration and Max silence duration to the same value, the length of the longest pauses you want to keep, probably at least a few hundred ms.
Set Threshold for silence to the threshold you want for detecting silence. You'll probably have to fiddle a bit with this unless you have somehow blanked the silences completely.
The effect is described here