I find the most versatile and comprehensive sound editing software to be Adobe Audition - a little like Photoshop in that you can use the basics or enter the learning curve and add to your skills and knowledge as you see fit.
I've tried several versions but find myself returning to one of the very earliest - 1.5 - more than adequate for my needs as it is capable of editing to the microsecond
I've never checked but have been told that Adobe have more or less given up the ghost with sound editing and are allowing free downloads of earlier versions - a must, if that's the case.
Jim Carroll