Modulation, is your voice driving the radio,,,but here's what I found:
modulation
DEFINITION - Modulation is the addition of information (or the signal) to an electronic or optical signal carrier. Modulation can be applied to direct current (mainly by turning it on and off), to alternating current, and to optical signals. One can think of blanket waving as a form of modulation used in smoke signal transmission (the carrier being a steady stream of smoke). Morse code, invented for telegraphy and still used in amateur radio, uses a binary (two-state) digital code similar to the code used by modern computers. For most of radio and telecommunication today, the carrier is alternating current (AC) in a given range of frequencies. Common modulation methods include:
* Amplitude modulation (AM), in which the voltage applied to the carrier is varied over time
* Frequency modulation (FM), in which the frequency of the carrier waveform is varied in small but meaningful amounts
* Phase modulation (PM), in which the natural flow of the alternating current waveform is delayed temporarily
