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 .