GM Genuine Audio Amplifiers are designed, engineered, and tested to rigorous standards, and are backed by General Motors. These amplifiers are part of the audio system, and is a GM-recommended replacement for your GM vehicle's original component. The purpose of the amplifier is to increase the power of a voltage or current signal. The output signal of an audio amplifier may consist of the same frequencies as the input signal or it may consist of only a portion of the frequencies, as in the case of a subwoofer or midrange speaker. The audio amplifier amplifies the signal and sends it to the appropriate speakers. Each of the audio output channel circuits (+ and −) at the audio amplifier have a DC bias voltage that is approximately one half of the battery voltage. The audio being played on the system is produced by a varying AC voltage that is centered around the DC bias voltage on the same circuit. The AC voltage is what causes the speaker cone to move and produce sound. Both the DC bias voltage and the AC voltage signals are needed for the audio system to properly produce sound. GM Genuine Parts are the true OE parts installed during the production of or validated by General Motors for GM vehicles. Some GM Genuine Parts may have formerly appeared as ACDelco GM Original Equipment (OE).