b. Retentivity. The ability of a substance to retain a magnetic force.
c. Coercivity. The ability of a material to resist demagnetization. With plastic-backed iron
oxide tape, permeability and retentivity are both present in more than ample amounts. However, this
kind of tape lacks coercivity when recorded at lower speeds. Chromium dioxide tape is a good example
of a highly coercive magnetic tape. At lower speeds this tape produces a much higher quality signal
than iron oxide tape.
3.
Frequency response. In addition to magnetic and mechanical properties, magnetic tape must
have electroacoustic properties. It is important that there be low noise, and that frequencies on the tape
be reproduced without variation.
a. Head to tape relationship: The materials used in making tape heads differ from those used in
making magnetic recording tape. The magnetic recording head must concentrate its magnetic field
effectively while the iron oxide tape must be able to absorb and retain the magnetic influences subjected
to it.
b. Contact between the sensitive (dull) side of the tape and the tape must be as close as possible.
Unsteady contact caused by "lumpy" oxide, dirt, or dust causes a loss of frequency response.
c. In recording, the iron oxide particles on the plastic backing arrange themselves in a pattern of
vertical stripes. The distance between each stripe is determined by the frequency of the magnetic
vibration, influenced by the sound signal.
4.
Tape uniformity. Uniform thickness of the magnetic layer is a primary requirement for a good
sound tape; any unevenness results in the recording and reproduction of a poor quality signal. The iron
oxide must be spread evenly over the entire surface of the tape and be thin enough to allow for equal
sensitivity to high and low frequencies. The iron oxide particles must be very fine if rapid changes in
frequency are to be recorded.
5.
Advantages and disadvantages.
a. Advantages. Magnetic recording tape provides the audio industry with several positive
features:
(1) Easy to use: Bulky recording equipment is not needed. Recorders no larger than the palm
of ones hand permit recording at locations where other methods cannot.
(2) Information storage: Several tracks of information can be recorded on magnetic tape and
be easily retrieved.
(3) Immediate playback: Recorded information can be played back immediately after it has
been recorded without special processing.
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