I assume you mean you want the blinds announced at the start of every round. So create an event, select "A level starts" for the trigger, and set the conditions to:
isRound and roundNum = 1
Change 1 to 2 for round 2, etc.
One caveat: for the first round, remember that you may have competing events. You may have an event to signal the start of the tournament, and you may have an event that sounds when the clock is unpaused. All 3 of these (including your event to announce the blinds for round 1) will be eligible to be fired when you start the tournament (the tournament starts, the clock becomes unpaused and round 1 starts). Only 1 can be selected, and the first one in your list of events will win. So make sure to move the one you want fired when the tournament starts closer to the top of the list.