Financial considerations are important in commercial radio production. Music royalty payments must be made to copyright holders when their music is used. Voice over artist fees typically start at £400 per hour but can be much higher for celebrity talent. Trafficking costs refer to the cost of airing an advertisement during prime listening hours between 6-10am and 5-9pm, which is more expensive due to larger audiences, versus overnight hours when audiences are smaller. Rate cards show large price differences between popular and unpopular airing times.