What type of modulation is characterized by changes in signal amplitude?

The type of modulation characterized by changes in signal amplitude is amplitude modulation. In this technique, the amplitude of a carrier wave is varied in proportion to the waveform being sent, such as an audio signal. This means that the strength or height of the wave changes to convey information.

For instance, in radio broadcasting, an audio signal alters the amplitude of a carrier wave, which allows the signal to be transmitted over distances. The variations in amplitude represent the different sounds and intensities of the original audio, making it possible to send complex audio signals effectively through radio frequencies.

Other modulation types such as frequency modulation involve varying the frequency of the carrier wave rather than its amplitude, and phase modulation alters the phase of the wave while keeping its amplitude constant. Time modulation, while less common, also does not focus on amplitude changes. These distinctions affirm why amplitude modulation specifically refers to changes in the signal's amplitude.