The best audio input device is the connection from the iPod line out to the car stereo line in. You can buy a connector that can carry audio signals from the line out of the iPod to the line in of the stereo. This allows you to hear your favorite tunes on the car stereo while driving. The sound quality is also good compared to other similar devices. Another input device you can use is a headphone jack. One end of the cable is connected to the headphone jack of an iPod, and the other end to the stereo line in. But this doesn’t have as good sound quality as compared to the iPod through the stereo car speakers.