When we are dealing with linear systems, the only way signals can be
combined is by scaling(multiplication of the signals by constants) followed by
addition. For instance, a signal cannot be multiplied by another signal. Figure
5-10 shows an example: three signals: , , and are added to form x
0
[n] x
1
[n] x
2
[n]
a fourth signal, . This process of combining signals through scaling and x [n]
addition is called synthesis.
Decompositionis the inverse operation of synthesis, where a single signal is
broken into two or more additive components. This is more involved than
synthesis, because there are infinite possible decompositions for any given
signal. For example, the numbers 15 and 25 can only be synthesized (added)
into the number 40. In comparison, the number 40 can be decomposed into:
or or , etc. 1 % 39 2 % 38 & 30.5 % 60 % 10.5
Now we come to the heart of DSP: superposition, the overall strategy for
understanding how signals and systems can be analyzed. Consider an inpu