The amplitude of the wave is then changed according to the strength of the signal being broadcasted. F requency Modulation is the most popular radio transmission technique used today. FM is so popular because it is able to transmit more of the sound that we want to here. AM has problems in transmitting sounds which are at higher frequencies, such as those created by a flute. Then the varying sound level causes frequency changes - The louder the sound, the frequency of the carrier wave increases.
Frequency modulation is shown in the figure below.
An important factor in FM is that the carrier signal has a constant amplitude.