The processor allows us to strip the music of the added equalisation that the car manufacturer added to it. Second, most premium audio systems divide up the music into bands, and then send that music to particular speakers, such as a subwoofer, midranges and tweeters.  To give you the best-sounding car audio system, we are going to need the capability of picking the exact sounds that each of your new speakers is going to reproduce. The processor will also allow us to sum the music back into one full-range signal. Now we have a musical signal to work with that is a perfect representation of the original recording.