A
sinusoid's frequency content may be graphed in the
frequency
domain as shown in Fig.
4.6.

figure[htbp]
An example of a particular sinusoid graphed in Fig.
4.6 is given by
where
That is, this sinusoid has amplitude 1, frequency 100 Hz, and phase
zero (or

, if

is defined as the
zero-phase
case).
Figure
4.6 can be viewed as a graph of the
magnitude
spectrum of

, or its
spectral magnitude representation
[
44]. Note that the
spectrum consists of two components
with amplitude

, one at frequency

Hz and the other at
frequency

Hz.
Phase is not shown in Fig.
4.6 at all. The phase of the
components could be written simply as labels next to the magnitude
arrows, or the magnitude arrows can be rotated ``into or out of the
page'' by the appropriate phase angle, as illustrated in
Fig.
4.16.
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