how to turn off auto fading of audio in imovie 2017?

Audio fade in and out is set by adjusting small circles that appear on the clips edges just above the volume line. Hover your mouse over the clip edge above the volume line and you will see a circle appear. Drag the circle to set the amount of fade. All the way to the clip edge will give you no fade. You can set fade using keyframes. place the cursor over the volume line where you want the keyframe and hold down the option key and click. This will place a keyframe. Place additional keyframes as you like and then drag the volume line down between the keyframes.

Hi,

I notice a tiny, almost imperceptible, fade occurring at the end of a trimmed back audio clip. If that is what you are referring to, it doesn't appear that there is any iMovie feature that can get rid of it, other than what Jim Wanamaker said. You can try raising the audio level at the end with the keyframe method and see if that helps. One thing that seems to work is to butt up another small audio clip against the end of the edited clip, and then mute the new clip.

-- Rich