Figure 1-6. Wavelength limitations in tape playback
When the wavelength equals the gap width, the cancellation is complete and the output is zero.
Thus, for a given gap width, the highest frequency that may be played back without cancellation has an
equivalent wavelength of twice the gap width. The limit can be extended by reducing the gap width,
increasing the recording speed, or both.
During playback, tape noise is present in the output at about 60db below saturation level. At
sufficiently high signal levels, the noise is unnoticeable. However, as the signal frequency is reduced,
the response falls and the signal-to-noise ratio decreases. This effect limits the relative bandwidth, or
the number of octaves between the highest and lowest frequencies. If the highest frequency is recorded
at saturation, the signal level at 10 octaves is 60db down or equal to the noise level. As a result, the
largest frequency spread that can be accommodated in a magnetic tape system is about 10 octaves.
Learning Event 4:
SOLVING PROBLEMS IN TELEVISION RECORDING
Frequency modulation, in television recording, is the video information that is placed on the tape
in the form of a frequency-modulated signal. This solves a number of problems as follows:
a. Since the video signal has a span greater than 18 octaves, and the largest span that can be
accommodated on tape is 10 octaves, direct video recording is not practical. This difficulty is overcome
by using a frequency modulator to change the video information into an FM signal. Although the