The action of changing alternating current to direct current is called:

Rectification is the electrical process of converting alternating current (AC), which periodically reverses direction, into direct current (DC), which flows in only one direction. This is typically achieved using diodes, which act as one-way valves for electric current. The other terms describe entirely different electronic processes. Transformation refers to changing the voltage levels of an AC signal using a transformer. Amplification is the process of increasing the power of a signal, while modulation involves varying one or more properties of a periodic waveform (like a radio wave) with a modulating signal to transmit information.