In signal processing, what does the term "modulate" refer to?

In signal processing, the term "modulate" specifically refers to varying parameters of a signal to encode information. This is commonly seen in communication systems where a carrier wave is altered in some way to convey data. Modulation can involve changing the amplitude, frequency, or phase of a carrier signal in accordance with the information signal being transmitted.

For instance, amplitude modulation varies the strength of the carrier wave, while frequency modulation alters the frequency of the carrier. These changes allow the information signal to be transmitted over a medium (like air or cable) more effectively, as they can help to improve transmission range and quality, resist interference, and facilitate multiplexing.

While other choices relate to characteristics of signal processing, they do not fully encapsulate the concept of modulation. Changing the strength of a signal is a specific type of modulation (amplitude modulation), whereas creating harmonics and multiplying frequency do not directly define modulation in the broader context of signal processing. Hence, varying parameters of a signal is the most comprehensive and accurate description of modulation.