Many people listen to recorded music as part of their everyday lives, e.g., from radio or TV programs, compact discs, downloads, or, increasingly, online streaming services. Sometimes we might want to remix the balance within the music, perhaps to make the vocals louder or to suppress an unwanted sound, or we might want to upmix a two-channel stereo recording to a 5.1-channel surround sound system. We might also want to change the spatial location of a musical instrument within the mix. All of these applications are relatively straightforward, provided we have access to separate sound channels (stems) for each musical audio object.