In which modulation method is the time interval between sine waves varied to reflect information signal variations?

The correct answer involves frequency modulation (FM), where the instantaneous frequency of the carrier wave is varied in accordance with the amplitude of the information signal. In this technique, the time intervals between the peaks of the sine waves (the carrier signal) change based on the data being transmitted, allowing for the encoding of information into the frequency of the wave.

Frequency modulation effectively alters the frequencies of the sine waves to represent variations in the signal. For instance, when the information signal indicates a higher amplitude, it corresponds to an increase in the frequency of the carrier wave. This creates a bandwidth that can accommodate complex sound and reduces the effects of noise compared to amplitude modulation, in which the amplitude of the wave is varied rather than the frequency.

In contrast, amplitude modulation (AM) varies the height (amplitude) of the waves, while phase modulation (PM) alters the phase of the wave rather than the frequency or amplitude. Digital modulation involves encoding data into the carrier signal but doesn't specifically refer to varying the time intervals of sine waves. Thus, frequency modulation is the method specifically characterized by varying the time intervals of sine waves to convey data.