A new Christmas album from Pentatonix has become a biannual holiday tradition. On this latest gift from the a cappella group, PTX once again conjure a winter wonderland with just their impossible voices, playfully harmonizing on both well-loved standards (a sparkling, choral take on “Jingle Bells”) and modern classics (beatboxing on Stevie Wonder’s “What Christmas Means to Me”). And as with their previous two holiday collections, they include some unexpected covers that still fit the mood, ranging from a wintry take on The Neighbourhood’s indie-pop hit “Sweater Weather” to a soul-stirring rendition of the Whitney Houston/Mariah Carey duet, “When You Believe,” featuring country singer Maren Morris.