Production sound mixer Julian Howarth talks about the complexities of recording sound underwater and in the world of Pandora, and why it was worth spending four months figuring out one sound. For a production sound mixer working on a typical production, four months might encompass the length of the entire shoot. On “ Avatar: Fire and Ash ,” production sound mixer Julian Howarth spent four months finding the best way to record a single sound: the first breath of air taken by actors as they