Audiofile Engineering "Triumph" is available from the Apple App Store or direct from Audiofile Engineering. It's not free but not expensive either. Their "Wave Editor" program will do this too, it's the previous version and would likely be less expensive if it still available.
"Sound Forge Pro" is available for Mac if you really want that but it is far from free. For free there's the cross platform "Audacity" if you really need free.