record voice in off in imovie

Possibly you do not have the microphone enabled for iMovie.

Go to System Preferences/Security & Privacy/Privacy and click on the Microphone item in the left side bar. Make sure that there is a checkmark next to iMovie.

-- Rich

Adding to my previous post: Click on the system setting symbol to the right of the red record button at the bottom of the preview screen. Make sure that the volume slider is moved to the right and that you have selected the correct microphone from the setting drop down menu.

[EDIT] If still no luck, try deleting preferences: To delete preferences open iMovie while holding down the Option and Command keys and select to delete preferences in the box that appears. iMovie will open in a new library. Reopen your old library to get back to your projects.  Deleting preferences is a safe procedure that will not cause data loss or disruption to your project.

-- Rich