a negative frequency

Hello, I am using the new download of audacity, and I am trying to make a negative frequency or sound wave. Can someone please give input on how to do this? This is better than protools :smiley:

Frequency measures something that happens in time, so you can’t have a negative frequency, but sound is vibrations in air, and you can make Audacity produce a sound track with the vibrations backwards.

Select a sound track and Effect > Invert