Menu insert grayed out
In classroom in a Book Audition CC Second Edition, Lesson 3 - Cut Copy Paste, position 1415 - I want to "choose Edit > Insert > Silence". But the menu-item 'insert' is grayed out. Only 'insert and mix' is available.
I have closed AU, started it again and loaded just one single audio-file. Also there 'insert' is grayed out.
What am I doing wrong?
Thanks
P.S. I hav'nt used AU for several years, so I want to refresh my knowledge by using the book.
