To make a magnetically striped print you must first ask a laboratory to prepare a mute print on single perforated stock. You can then arrange for a coating of ferrous oxide to be applied to the edge of the film opposite the sprocket holes. The master magnetic final mix, recorded in the dubbing theatre, can then be replayed on one machine and simultaneously re-recorded on the magnetically striped print. Care must be taken to record the track with the correct sound advance as we shall see in a moment. This laborious process has to be carried out for every single print. Combined optical sound copies are easily produced in bulk. They are also considerably cheaper.