What is signal modulation?

Signal modulation refers to the technique of modifying a carrier signal, which is usually a sine wave, in order to encode information that can be transmitted over a communication medium. This process allows for the efficient transmission of data, whether it's audio, video, or other types of information.

In modulation, specific characteristics of the carrier signal—such as its amplitude, frequency, or phase—are varied according to the information signal. For example, in amplitude modulation (AM), the amplitude of the carrier wave is changed proportionally to the information signal, while in frequency modulation (FM), it is the frequency of the carrier wave that varies. This modification makes it possible to send data over longer distances and helps in multiplexing multiple signals over a single channel, thereby maximizing the use of available bandwidth.

The other choices represent concepts that, while related to signal transmission, do not specifically capture the essence of modulation. Amplifying audio signals pertains to increasing the strength of the signal rather than modifying it with additional information. Reducing noise in a transmission line focuses on improving the clarity and quality of signals rather than encoding information. Enhancing the bandwidth of a digital signal refers to increasing the amount of data that can be transmitted but doesn't involve the modulation of a carrier signal itself.