Which modulation technique is associated with changing the amplitude of the signal?

The modulation technique that involves changing the amplitude of the signal is amplitude modulation. In this technique, the information signal, which could be audio or any other form of input, is superimposed onto a carrier wave by varying the amplitude of the carrier in proportion to the amplitude of the input signal. This results in a wave where the height (amplitude) reflects the variations of the modulating signal.

In practical terms, amplitude modulation is widely used in analog broadcasting, such as AM radio. The amplitude of the carrier wave is adjusted according to the sound signals, which allows the transmission of audio information over radio frequencies.

Other modulation techniques you might encounter serve different purposes, such as frequency modulation, which alters the frequency of the carrier signal in accordance with the input, or phase modulation, where the phase of the carrier wave is varied to encode the signal. Pulse modulation, on the other hand, involves the encoding of data in a series of pulses, focusing on variations over time rather than a continuous wave's amplitude or frequency characteristics.