adjusting varying audio levels

In an effort to improve my audio files, I am looking at the overall audio quality. I do phone interviews, that last for a full hour. Frequently we start out fine, and the levels are good. However guests often start out with a great volume for the first part of the response, but by the time sentance three comes out they are tailing off volume wise. My last guest was incredibly variable from very good to barely audible in one response. I have tried highlighting the low segments, and raising the gain, but that seems to increase the whole 15 min segment. How do I increase gain in just that one 2min segment when I need it, and leave the rest at the right level. I also recall someone mentioning an external program that adjusts overall variable levels to a more even level.

This is not an automated solution which adjusts the whole track, but…
0) listen to the loud portion just before the quiet portion so your ear know how loud to make the change

  1. select (drag with the mouse) the audio which needs to be louder (it might make sense to give this a temporary region label)
  2. choose menu Effect > Amplify…
  3. a dialog opens–for now just accept the default values and click Preview–how does it sound–too quiet, increase the value in the “Amplification (dB)” box–too loud decrease the value
  4. once you are happy click OK
  5. drag select from a bit before and a good bit of the changed section --play it, if happy fix another section, otherwise, undo that effect (menu Edit > Undo or your shortcut key) and try again

You could make loud sections more quiet the same way by selecting them and using the Amplify effect and lowering the value in that top box.