Defining loop lenght!?

Hello Guys,

Just got a quick question for which i havent found anything on this forum (i'm new here!)

So simply, I'd like to define the number of bars I want my loops to be.

Say 4 bar for example. After it reaches that 4 bar, i'd like the loop to automatically enter Overdub or play mode (without me pressing anything)

How could I do that? :)

Thanks,

Nell