What type of modulation technique is known for varying the duration of the pulse to convey signal information?

Pulse-width modulation (PWM) is the correct answer as it specifically involves varying the width or duration of the pulses in a signal to encode information. This technique is commonly used in various applications, including motor control, lighting dimming, and audio signal processing, because it allows for efficient power management and signal representation.

In PWM, the width of the pulses is altered while maintaining a constant pulse frequency. By changing the duration of the pulses relative to a given period, it conveys different levels of information, such as brightness in LEDs or speed in motors, depending on the width of each pulse relative to the total period.

This method is distinct from other modulation techniques such as frequency modulation, where the frequency of the carrier signal is varied; amplitude modulation, which alters the amplitude; and phase modulation, which changes the phase of the carrier signal. Each of these techniques encodes information differently, but none utilizes pulse duration as a primary means of conveying signal information like pulse-width modulation does.