USB connectivity is just one of the many features that new cars and aftermarket head units often come with these days that weren’t available just a few years ago. Some of these features are harder to crack than others, in terms of adding them to older head units without having to shell out an expensive upgrade, but there are actually two ways that USB can be added to an older head unit without too much hassle. The easiest way to add USB to a head unit is to plug in an FM transmitter that has a built-in USB port, but there is another way that will provide much better sound quality if the head unit already has an auxiliary input.

While USB may seem like just another type of auxiliary input, there’s actually more going on under the hood than many people realize. Regular auxiliary inputs require an analog signal from a device like a satellite radio, CD player, or MP3 player, which is fine, but USB allows a device to offload digital audio data to a head unit and let it do the heavy lifting. This is why you can typically plug a USB drive with songs on it, but not an MP3 player hardware, into a USB head unit and play music directly from the storage media.

This is also why USB to aux cables don’t work as you’d expect or hope. If you plug the USB end into a device that can only passively access stored content over the USB connection, nothing will come out the other end. There are exceptions, such as phones and MP3 players that can actually output an analog audio signal through their USB ports, but that’s not very common and defeats the purpose of using a USB connection to connect to a car stereo in the first place.

The easiest way to add a USB connection to a car stereo is to simply use an FM transmitter with a USB port. This is a true plug and play solution that requires no installation work. All you need to do is plug the transmitter into a power outlet, connect your phone, MP3 player or USB stick to the transmitter and tune your car stereo to an empty space on the dial.