Sync button greyed out

Hi, i´m new to blender. I usually work with other 3d programs but now i was requested to do a couple animations with this program. Basically, i´m terrified.
So after playing back my first sketch animation i noticed it was not in real time.
After a quick look i found that if you click on the audio setup the button “Sync” it would play in real time but when i open the tab the Sync button is greyed out and i can´t activate it.
Any clues?