Page "Analog signal" Paragraph 9

Another method of conveying an analog signal is to use modulation.

In this, some base signal ( e. g., a sinusoidal carrier wave ) has one of its properties modulated: amplitude modulation involves altering the amplitude of a sinusoidal voltage waveform by the source information, frequency modulation changes the frequency.

Other techniques, such as changing the phase of the base signal also work.