Which of the following is a common type of signal modulation?

Amplitude modulation (AM) is a widely used method for encoding information in the amplitude of a carrier wave. In AM, the amplitude of the carrier signal is varied in proportion to the message signal, which can be audio, video, or data. This technique is particularly prevalent in radio broadcasting, where it allows audio signals to be transmitted over long distances. The advantage of AM is that it can be easily demodulated, which makes it ideal for applications like AM radio.

While phase modulation (PM) is also a legitimate modulation technique, it is less common in audio broadcasting compared to AM and often used in digital communications. Time division modulation (TDM) refers more to a method of multiplexing signals rather than a modulation type, while bit modulation (BM) is not established terminology in widely recognized communication systems. Thus, AM stands out as the primary example of common signal modulation in practice.