An audio amplifier is an electronic device that increases the level of an audio signal (the strength of the signal). It amplifies the signal from a source such as a radio or CD player, and transmits it to speakers. This can increase the volume of the signal allowing the listener to hear the audio content with greater clarity. Audio amplifiers can include features such as equalization, tone control, and other sound-shaping features. They can also be used to drive headphones, headphones amplifiers, and other audio devices.