Technical bit

Laserdiscs can be recorded in two ways, CLV (constant linear velocity) offering around an hour per side, or CAV (constant angular velocity) offering just over 30 minutes per side. CAV discs offer slightly better quality, and various trick play functions, but most films come in the longer CLV format, because no-one wants to get up to change disks in the middle of the really scary bit.

UK PAL Laserdiscs require a bit more room to store the video signal than US NTSC Laserdiscs, so to fit it all on the disks, the original analogue FM stereo soundtrack was removed from all recent discs in favour of the superior digital stereo soundtrack. However, the leaner US NTSC video format allows the analogue FM stereo soundtrack to sit side by side with the newer digital stereo.

So what, who needs two versions of the same sound track? Those cunning film producers have found another use for the analogue soundtrack. Why not get the director, actors, or other key members of the production team to commentate the movie, with facts, tips and anecdotes? Stick this on the analogue channel and leave it up to the viewer to decide whether they want to see the film as normal, or press a button, swap soundtracks and have a unique and exclusive movie documentary.

Laserdisc is currently the only medium that stores the latest digital cinema sound systems, such as Dolby Digital and DTS (Digital Theater Systems). DTS Laserdiscs, expected to be on sale this year, store their soundtrack in the same place as the conventional digital stereo, resulting in titles incompatible with anything other than a DTS system. But Dolby Digital, charmingly known as AC-3 in the home, is a highly compressed system, which, believe it or not, can sit on just one of the old analogue FM channels. Consequently you can buy Laserdisc titles with AC-3, conventional digital stereo, and even have a single analogue FM mono channel for running commentary.