Access your entire music or podcast library on the road.
Control on phone from the interface on your head unit.
Only works with iOS devices.
Some head units are specifically designed for use with iPods.osaMu /Flickr (Creative Commons 2.0)
Not available on a lot of head units.
The ideal connection for an iOS machine is through a compatible head unit with Apple CarPlay.
Built-in iOS controls are also available on a number of aftermarket head units.
USB connections in cars work with most phones and MP3 players.knape / Getty Images
Once connected, you’re able to view and select songs through the head unit controls.
Easy to plug in when you start driving and unplug when you’ve arrived.
Compatibility far from universal.
Many head units can be paired with mobile devices via Bluetooth.iPhoneHacks.com
Older vehicles may require additional accessories.
You will need to supply the cord that works with your gear.
Sound quality not as great as USB.
Plugging in an MP3 player or phone via an auxiliary input is one way to go, but it may not provide the best sound.PraxisPhotography / Getty Images
Bluetooth can deliver the same head unit interface and functionality as a USB connection but without the wires.
Bluetooth is increasingly common in vehicle head units.
However, because most of these interfaces also have USB outputs, most people opt for the latter.
Cassette tape adapters weren’t meant for use with MP3 players, but they’ll do in a pinch.Baturay Tungur / Getty Images
Bluetooth is generally preferable to Aux inputs because they allow for hands-free control.
Sound quality generally inferior to USB connections.
Can’t be controlled from the head unit.
An FM broadcaster or modulator is a sure-fire way to listen to MP3s on any car radio, but there are drawbacks.Kyu Oh / Getty Images
Some head units don’t have USB outputs, neither do some (very old) MP3 players.
Thankfully, Aux inputs are nearly universal.
You will need a cable with two 3.5mm male ends.
Make the connection and pick the Aux audio source on the head unit.
Audiophiles may also notice inferior sound due to the lossy compression of digital-to-analog audio.
Easy to set up.
Sound quality is not great.
Cluttered presentation with wire hanging out of the tape player.
These adapters were originally used with portable CD players, but they work just as well with MP3 players.
They look like cassette tapes, except they don’t actually contain any tape.
Audio is transferred via a cable to the adapter and then passed through the tape heads.
Most Universal Solution: FM Transmitter
Kyu Oh / Getty Images
Works with any FM car radio.
Does not work well in areas with a lot of FM radio traffic.
The last way to connect an MP3 player to a car is with an FM transmitter or modulator.
FM transmitters broadcast very weak FM signals that your head unit can pick up.
Most FM transmitters plug into an MP3 player just like a cassette adapter or auxiliary input.
Some FM transmitters useBluetooth technology.
These devices can be paired with MP3 players or phone that are also Bluetooth-compatible.
This allows for a wireless interface between your media player and stereo.
If your radio does not have anauxiliaryinput, an FM modulator is likely the next best thing.
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