CLV and CAV

There are a number of features on the laserdisc player or DVD that you should be on the lookout for. First, it should have the capacity to perform visual search forward and reverse (you see the image moving quickly forward or backward, to relocate an interesting scene), and to freeze single frames. This should be capable in both the CLV (Constant Linear Velocity) and CAV (Constant Angular Velocity) formats for LD players (DVD players only use one format). Constant Linear Velocity means that the laser beam is reading data along the spiral track at a constant speed (11 meters per second for laserdisc, 1.2 meters per second for compact disc). As the track spirals from the center of the laserdisc to the outside edge, the rotation speed has to slow down from 1800rpm to 600rpm (500rpm to 200rpm for compact disc), in order to maintain this constant linear velocity of reading the data (the circumference of the outer edge is greater than it is at the center). Constant Angular Velocity means that the angle between a line drawn perpendicular to the radius and through the spot where the laser beam is reading data, and the curve of the spiral track, remains essentially constant. In practical terms, this just means that the CAV disc rotates at a constant speed all the time (1800rpm). LPs, then, would also be considered a type of CAV disc, rotating at a constant 33 1/3 rpm.

Compact Discs are fundamentally in the CLV format, and because there are only two digital sound tracks on them, compared to one video and four audio tracks for a laserdisc, a compact disc can fit about 1 hour of music on a 5 inch disc. Most laserdisc movies are produced in the CLV format, because it allows 1 hour of movie to be stored on each side of the 12 inch disc (unlike CDs, the LD has information on both sides). In the CAV format, only 30 minutes of movie per side can be stored on laserdiscs. All laserdisc players can perform the visual search and freeze frame functions on CAV laserdiscs. However, only the higher quality players can do these things on a CLV disc. All DVD players have the search function. Being able to do fast forward or reverse, and see the image while doing so, is very handy when you see something you want to watch over again, and especially if you want to view a special effect frame by frame. So, if these features are important to you, be sure to check that the laserdisc player you are considering for purchase can perform them on CLV discs.