What method is used to convert a digital signal to analog and vice versa?

The method used to convert a digital signal to analog and vice versa is Pulse Width Modulation (PWM). This technique involves varying the width of the pulses in a signal to encode information, making it particularly useful for controlling analog devices with digital signals. In PWM, the width of the pulses corresponds to the amplitude of the original analog signal. When used for digital-to-analog conversion, the varying pulse widths can recreate the original waveform of the analog signal by turning the digital signal into a series of on-off states, which, when filtered, result in a smooth output.

Pulse Width Modulation is widely employed because it allows for efficient transmission and minimizes signal distortion. It's commonly used in applications like motor control and audio signal processing. The other methods listed, while they involve modulation techniques, are primarily focused on varying different aspects of the signal (like frequency or amplitude) rather than offering a direct means of converting digital signals to analog or vice versa in the same practical manner that PWM does.