PLAYBACK is the industry standard term for a backing track (a musical recording with the vocal performance missing). Our backing tracks are produced to a very high standard and are as 'soundalike' to the original popular recordings as possible.
+b/vox means 'plus backing vocals' which is the musical backing PLUS all non-lead vocals.
VOCAL GUIDE or COMPLETE is a version of our backing track WITH the lead vocal part performed on top — these COMPLETE versions are available to you strictly as a guide for you to learn the song and are not intended to be played or performed publicly.
MULTIPLEX is a special format where the backing track is on one channel of the audio, with the vocal guide on the other. This allows you to use your audio playback system's "balance" control to dial in the lead vocal to help you out when practising the song.