from howstuffworks:
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 mm/s), 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 therefore 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.
The answer is, head gap wear, dirt, misalignment, and overall losses have a much more profound effect on highs than on lows. This is true even though the high frequency signal output at the head is many decibels higher than the low frequency response.
Newer heads, as well as all modern heads, are made of ferrite.
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