Digital Sound & Music: Concepts, Applications, & Science, Chapter 6, last updated 6/25/2013
55
axis([0 132300 -2 2]);
figure;
plot(m);
axis([0 132300 -2 2]);
figure;
plot(AM3);
axis([0 132300 -2 2]);
wavplay(c, 44100);
wavplay(m, 44100);
wavplay(AM3, 44100);
carrier wave
,modulator wave
result of amplitude modulation
Figure 6.51 Amplitude modulation of a complex audio signal
with carrier and modulator waves reversed
Amplitude modulation produces new frequency components in the resulting waveform at
and , where is the frequency of the carrier and is the frequency of the
modulator. These are called sidebands. You can verify that the sidebands are at and
with a little math based on the properties of sines and cosines.
(The third step comes from the cosine product rule.) This derivation shows that there are three
frequency components: one with frequency , a second with frequency , and a third with
frequency .
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