I've finished editing my film on Final Cut Pro and have been asked for a master copy with an audio reference tone (frequency 1KHz at a level of 20dbFS=+4dbu=0vu). What does this tone mean for broadcast?
Is it the limit the volume of my film should reach or the average volume?
So do I have to adapt the volume level of my film accordingly.
It's very similar to how an orchestra uses a reference pitch (A440, for one). That pitch is heard by each member of the orchestra and gives them all the same point to reference off of so that they can tune their instruments to play in the same key.
The reference tone allows the engineer to say, "Aha! When my meter says '0dB', it actually means +4dBu/-20dBFS!".
Hope that makes sense...corrections & additions welcome.
How do you know what constitutes "-12dBFS"? Well, you looked at your meters to make sure. The point behind the reference tone is to make sure that "-12dBFS" on your meters is the same as -12dBFS on their meters. That way, the audio will be a perfectly accurate transfer of what you recorded/mixed.
Visual Example -
On both meters, the vertical lines represent "-12dBFS". We can also see that -12dBFS is marked at different places on the two sets of meters.
The reference/calibration tone ensures that when "Their Meters" say -12dBFS it is the same as "Your Meters" saying -12dBFS.