How to reverse audio
Drop in a file. Reverse is already on, so Play selection plays it backwards straight away. Drag the handles to choose a part: a selection from 0:10 to 0:15 plays from 0:15 back to 0:10. Then save it as MP3, WAV, AIFF or Opus.
Fades and speed with it
Fades follow the reversed sound as you hear it: a fade in softens the start of the backwards clip, which was the end of the original. Speed works too, and changes the pitch with it: a reversed voice at 0.75× comes out slower and deeper.
What changes
Only the order of the sound. Every channel is turned round sample by sample, so stereo keeps its left and right, and reversing twice gives back the original. Saving as MP3 encodes it, which loses a little; WAV keeps it exact.
Questions
Can I reverse one part and keep the rest forwards?
No. The saved file is only the selected part, reversed. Splicing it back into the song needs a multitrack editor.
Can it reverse the sound of a video?
The sound only: drop in an MP4, MOV or WebM and its soundtrack is saved backwards as an audio file. The picture is not kept.
How do I hear it forwards again?
Switch Reverse off and play. The original file is never changed, only the copy you save.