Leave out the cookies and a glass of milk for Pentatonix, who are back with their 11th festive project, Christmas in the City. Come down the chimney for an array of presents: harmonies of old classics (a big-band take on Burl Ives’ “Holly Jolly Christmas,” or a rousing “Silver Bells”) and gift-wrapped originals (“Bah Humbug,” which reinvents Ebenezer Scrooge’s story, as well as a chronicle of the Elf on the Shelf phenomenon aptly called “Elf”). A few of Santa’s friends join to deck the halls: JoJo lends herself to the sentimental “Snowing in Paris” and the a cappella group revives Frank Sinatra for a posthumous duet on “I’ve Got My Love to Keep Me Warm.” Ol’ Blue Eyes becomes the third ghost of Christmases past tapped by PTX, following Elvis Presley (“O Little Town of Bethlehem”) and Bing Crosby (“White Christmas”) on previous seasonal albums. And one special offering under the tree? “Moody Rudy,” a mashup of Chuck Berry’s “Run Rudolph Run” with Glen Miller’s “In the Mood.”