 In providing instrumentation for the record , Kurstin used all of his instruments such as a <unk> and a <unk> , taping them from a distance to stimulate the Wall of Sound , a recording technique originally developed by Phil Spector that was popular in the early 1960s . He enlisted Clarkson to provide all the background vocals herself . Clarkson , who grew up singing in a chorus , was pleased with the aspect ; saying , " <unk> is something I knew how to do from childhood . Sometimes I 'd have to do an alto instead of a soprano because they needed a bigger sound . But I 've never had to do anything like this before — doing all my backup vocals , essentially being my own choir . " Together , they began to record in May 2013 and continued through the summer of that year , beginning by recording " White Christmas " with Clarkson in the vocal booth and with Kurstin on a piano . She commented , " The production is all him . I would be just like ' Hey , can we make this more jazz ? Hey , can we make this more <unk> . And he just , like Harry Potter , made this happen . It 's so weird . " 
