Amplitude modulation affects which aspect of a carrier signal?

Amplitude modulation primarily alters the amplitude of a carrier signal while keeping its frequency and phase constant. In the context of amplitude modulation (AM), the modulation process involves varying the strength (amplitude) of the carrier wave in accordance with the information signal, such as audio or other data. This change in amplitude allows the information to be transmitted alongside the carrier signal.

When an information signal is applied to the carrier, the peaks (or crests) of the wave become higher and lower depending on the modulation, effectively encoding the information in the amplitude variations. This characteristic of AM is what distinguishes it from other modulation techniques that may alter frequency or phase instead.

Understanding the principle of amplitude modulation is crucial, especially in fields like telecommunications, where it is used for broadcasting audio signals over distances. In summary, the correct answer is indeed the alteration of amplitude, as it encapsulates the fundamental nature of the amplitude modulation process.