An Appplication of Digital Technology to Stereo Broadcast Post Production

The post-production of sound, known as "dubbing", was from the sixties until the early seventies, mixed using magnetic film sound stock in a film dubbing theatre.Still very successful and very much in use, the film dubbing theatre is equipped with several sprocketed replay channels , anywhere between three to thirty five machines.They feed the sound through the mixing desk on to one or two sprocketed magnetic recorders.These machines, 35mm, 17.5mm, or 16mm.are linked either electrically via three-phase selsyn motors or electronically through stepping motors.The ability to run the tape backwards and forwards, "rock and roll", and drop back into record, "punch in", allows the dubbing mixer to work through the programme, stopping as each mistake in the mix is made, roll back, and pick up again.The modern film dubbing theatre can rock and roll at very high speeds, up to thirty times replay speed, in either direction and maintain almost perfect look at all times when running at these speeds.The sound tracks are laid up before the dubbing process on comparatively simple editing tables.This allows the dubbing editor to try different music.sound effects, or dialogue against the picture without using expensive dubbing time.The tracks can be moved easily backwards and forwards against the picture, and each other, either by editing in, or out lengths of film spacing.They can also be unlocked and physically moved in the dubbing theatre.16mm magnetic film, the main medium used in television, has a rather limited band width, about 50Hz to HRH: within one or two dB.The signal to-noise ratio is about deB without noise reduction.Drop-out frequency is also extremely high as the tape base is rather thick and the magnetic coating .relativelycrude.None the less film dubbing is a very fast and powerful postproduction sound process.