Metra FM Modulator Clear Hi Fidelity sound with direct antenna connection instead of using a cheap noisy FM transmitter type adapters. Connect and Play your MP3 Player, CD or Audio/Video system through a Highly Reliability PLL Synthesized Tuning circuit.. FM input modulator with 2 selections of frequencies (87.9 and 88.3). Connects through your vehicle's antenna system so you can control the volume with your stereo controls. Built In Noise Filter highly isolates from non-essential frequencies. Automatically switches from your Radio to your MP3, CD or Audio/Video player etc., when volume is adjusted to 60% (no on/off switch is required).