Warm up to the commitment “If you’re going to be an actor, you have to be a vocal athlete. One six-week vocal course isn’t going to cut it. I recommend a minimum of 30 minutes, three times a week.

For his role as country singer Jackson Maine in “A Star Is Born,” Bradley Cooper spent 20 hours a week training his voice. While it may be—to paraphrase the film’s lead song—hard keeping it so ...