How VCRs Work

By: Marshall Brain  | 

VCR Talk

Now that you know something about a VCR, you can understand several of the controls and terms used with VCRs:

  • Tracking control: The tape contains a linear control track that helps the VCR synchronize the rotating heads with the actual bands recorded on the tape. When you adjust the tracking control, you are skewing the relationship between the control track and the heads to try to get a closer match to the bands on the tape.
  • Flying erase head: VCRs have two types of erase heads. The low-cost kind simply erases the entire half-inch wide tape. This can cause a lot of snow between different segments recorded on the tape. A flying erase head is mounted on the rotating drum. It is able to erase bands individually, allowing very clean splices between segments.
  • SP, LP and EP settings: The three speed settings on a normal VCR simply control the speed of the tape with relation to the rotating drum. In SP mode, the tape is moving past the head at 1.31 linear inches (33.35 mm) per second. In LP mode, it's 0.66 ips (16.7 mmps), and in EP mode it is 0.44 ips (11.12 mmps). As the tape speed decreases, the bands on the tape get closer together, reducing the quality of the image but increasing the amount of material that fits on the tape.
  • Four-head vs. two-head: A VCR needs only two heads to record or play back a tape at SP speeds. A problem arises, however, at LP and EP speeds because the tape is moving much more slowly. Many VCRs include two wider heads for SP speed and two narrow heads for use at slower tape speeds. These four-head systems offer better performance at slower tape speeds.
  • End-of-tape sensing: The leader on video tapes is clear. A VCR shines a light through the tape and can detect the end of the tape when it "sees" the clear leader.


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