Amplitude modulation (AM)

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Amplitude modulation occurs when the amplitude of one waveform, the carrier, is modulated by the frequency of another waveform, the modulator.

 

cascading harmonics

 

If the frequency of the modulator is within the sub-audio range the result is tremolo.

If the frequency of the modulator is within the audio range new frequencies are created around the carrier.

 

These added frequencies are called sidebands and are composed of the sums and differences of all the frequency components of the source signals.

 

Amplitude modulation results in the same spectrum as multiplicative or   ring modulation with the addition of at least one of the original signals.