This weekend I am preparing to record a choir put together by Robbie Bundle for his title track from the upcoming album, My Sacred Place. There are several techniques historically used to record choirs singing to a backing track, played back through speakers with the polarity of the speakers reversed. This method allowed the in-phase vocals to remain whilst the out-of-phase backing music is phase-cancelled during mixdown. Although fairly effective it was only truly successful if the backing track was exactly the same as the final mix before the choir parts were added. So now in 2013 the method I will use is still based on phase cancellation but somewhat more successful. The choir will rehearse with the backing track and once the playback level of the track is determined I shall record the backing track only in the record space, not altering anything in regards to microphone level or position. Then recording the choir under the exact same settings. In post-production the recording of the backing track spill only will be phase reversed. When it is at the equal level as the spill on the choir recordings but opposite in phase it should be completely phase-cancelled. Gotta love a bit of physics as an audio engineer!