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Lead image

What's the best way to play music in the car?

Bluetooth vs USB — which sounds best?

In this article, we'll discuss the best options for playing music from your phone or other device in the car. Hint: USB connection provides the best sound while Bluetooth streaming is the most convenient. Get the details below.  

In the old days, it was easy: CD sounds better than cassette. And that's all there was to it. To get the best sounding music, you'd fumble through your CD wallet and listen to the lucky winner on your car stereo (and you still might). Today, we can choose from a wide variety of music sources (streaming over your iPhone or Android smartphone, portable audio players, USB drives, satellite radio tuners, and more), and also from an array of ways for piping the music from your favorite source into your car stereo.

The question is, how do you determine the best way to listen to your digital music? Some ways are easier than others and some ways will yield better sound than others. So, it really comes down to how you access and play your digital music and getting as much detail out of it as you can. Let’s take a look at the variety of ways to access your favorite tunes while on the road.

The most common ways to listen to music in the car are:

  • USB input
  • auxiliary input
  • Bluetooth® streaming 
  • WiFi
  • FM modulator

Which listening method sounds better?

While the best connection for audio fidelity is a direct or wired connection, there’s a lot to be said about wireless convenience and an ever-growing number of stereos that include built-in WiFi for use with Apple CarPlay® and Android Auto™ interfaces. 

usb input

Some USB ports are right on the front for easy access, while others are on the rear panel for a cleaner looking installation.

USB inputs — the preferred connection

The USB input is now a common feature on aftermarket car stereos, as well as in many factory systems. And that's a very handy thing because the USB input provides the best sound quality possible from an external music source, be it your phone, a portable high-res music player, or a simple USB flash drive loaded with your favorite tunes.

The music signal remains in a digital form until it gets converted into an analog signal by your stereo, so no unnecessary manipulations are made to it. USB doesn't limit the frequency response or signal-to-noise ratio of the music, so what you hear is exactly what your streaming music services or your stored music files are delivering. And besides being the best-sounding form of input, the USB input will often serve as a power source for your device too.

But if you’re keeping your factory radio and it does not already have a USB input, tell us what kind of vehicle you drive. We'll let you know if we have a USB adapter for your factory stereo, as well as the types of music files it’s compatible with. 

Auxiliary Input

Your stereo's auxiliary input is one of the easiest ways to play your music in the car.

Auxiliary inputs — the common connection

Feeding the sound through an auxiliary input will usually yield a strong signal because it's a direct audio connection with full-bandwidth (20-20kHz) frequency response, which is the range of perfect human hearing. An auxiliary input won’t degrade the audio signal, because it’s a direct delivery of the signal from the source to the car stereo, without any unnecessary electronic manipulations. So, it’s important to make sure your source is a good one by adjusting the settings in your streaming service or making sure you use music files with less or no compression when compiling your library.

Aux vs USB inputs

It would seem that auxiliary and USB inputs should deliver the same quality of sound, but frequently, they don't. One reason is the difference between the digital-to-analog converter (DAC) in your stereo compared to the converter in your music player. When you use your music player's headphone jack to connect to your stereo that means you're using the music player's DAC.

Unless you're using a high-resolution portable audio player or an add-on DAC for your phone, the DAC in the stereo is going to be superior to the one in the music player because car stereos have the power required for bigger, better sound over car speakers, so the DAC has to be able to reproduce a high-quality signal. Smartphones and older portable music players on the other hand, like the iPod®, were originally designed only to make small earphones sound pretty good.

 
Bluetooth audio streaming

Bluetooth® audio streaming — the wireless option

Bluetooth wireless technology gives you the convenience of streaming music to your stereo without a cable. The Bluetooth functionality is either built into your smartphone and car stereo, or added to the stereo using a Bluetooth adapter.

Bluetooth streaming vs FM transmitters

Bluetooth streaming is superior to most FM transmitters (the previous form of wireless connection, see below). First of all, Bluetooth signals are digital transmissions. They can carry more information and thus render better sound quality than FM transmissions.

Secondly, the way the Bluetooth signal is tranmitted greatly reduces the amount of interference from outside signals that often happens with FM. Bluetooth technology uses "spread spectrum" transmissions to broadcast parts of the signal over a constantly changing range of coded frequencies. As a bonus, this frequency-hopping also prevents your signal from being picked up on another piece of gear.

Let's take a look at the numbers. Bluetooth transmissions are full-bandwidth, having a frequency response of 20-20kHz. The signal-to-noise ratio is dependent on the source player, so that number will vary. As a high-quality, short-range, digital transmission, the Bluetooth process itself has little or no impact on the sound quality.

Bluetooth streaming vs USB input

While it is a good wireless option, Bluetooth's sound quality is usually not as good as a direct USB connection. Bluetooth offers higher resolution than MP3 music (320 kbps), but it doesn't offer the same resolution as high-res music or even CDs, like USB does. Check out our article about Bluetooth codecs for more information.

The downsides to Bluetooth streaming are minor. While the signal is resistant to interference, it does sometimes happen and you could get some form of unwanted noise on occasion. The other knock has been its range of 30', but in a vehicle, that's generally not a problem. Using Bluetooth streaming will drain your device's battery faster, so it's wise to have a charger handy.

[Learn how to add Bluetooth streaming to your car.]

 
car stereo with WiFi connection

Many new stereos offer wireless Apple CarPlay and Android Auto, which use a WiFi connection to your phone

WiFi and wireless audio

WiFi is the newer kid on the block, primarily in the form of car stereos that offer wireless Apple CarPlay for iPhones and wireless Android Auto for Android phones. Many folks don’t want to have to plug in their phones when they hop in the car, and who can blame them? That’s where WiFi comes in handy to create a small wireless network in your vehicle.

As for audio quality, you can get great high-res results from streaming and stored music on your smartphone when using WiFi. And if you’re using high-res settings for your music, there's no degradation in the audio over a WiFi connection. As with Bluetooth, the one thing to keep an eye on is your phone’s battery draining while going wireless.

FM transmitter

A wired FM modulator is one of the easiest ways to get your music into a factory radio with no auxiliary or USB input

FM transmitters and adapters

First, some numbers. FM radio is restricted (by FCC regulation) to a frequency response of 30-15kHz, which is not full frequency response. When you use an FM adapter to pipe in your tunes, the music is fed into your radio over an FM frequency — the radio thinks it's just another radio station. So theoretically, we can expect the music from our portable to sound about as good as a typical FM station.

There are two types of FM adapters to choose from, wireless and wired FM transmitters. A wireless FM transmitter broadcasts your music over the air to the stereo's FM tuner, just like the real incoming radio signals. It's easier to install but the wireless transmitter is directly competing with all of those radio signals and other FM interference bouncing around inside and outside of your car. So while they're convenient, you can expect some sound interference, especially in populated areas.

A wired FM modulator is directly connected to your radio via the FM antenna connection. It usually requires removing the stereo to get to the antenna connector on the rear (and maybe adding an antenna adapter, depending on your vehicle), but it's much less prone to outside interference than wireless transmitters. So, we can expect that of the two FM options, a wired transmitter will be our better bet for sound quality. 

Receiver in dash

The bottom line for best sound quality

  • A direct connection via USB will yield wonderful results because it eliminates extra manipulations of the audio signal.

  • WiFi provides the wireless convenience, smartphone integration, and excellent sound quality, but it’s often found on higher-priced car stereos.

  • Bluetooth streaming is a great wireless option and can be found on more affordable stereos and factory radios. However, it does manipulate the signal by broadcasting it over the air. And while it doesn’t reach the the bit rates of high-res or CD music, it still offers better resolution than standard MP3 resolution.

  • An auxiliary input is the next best “hardwired” option. It's also one of the most common inputs in a car audio system and one of the easiest methods to use. Consider a DAC for your phone (or using a portable high-res player) to make it even better.

  • FM adapters offer lower sound quality and are open to outside interference, but they are an option if no other connectivity is available for a stereo.

The quality of the source matters

Ever hear the expression “garbage in, garbage out”? Something to think about is how you encode your music to digital files. Music with less compression (CDs, high-res digital music, etc.) will sound better than music that's heavily compressed (MP3's, Internet radio stations, etc.).

If you're ripping a CD to a digital file for a USB drive or portable player, you can set the encoding for less compression on many programs, like Windows Media Player® and iTunes®. Likewise, Internet radio stations like TIDAL, Qobuz, and Amazon Music often let you set a higher quality (usually with a “premium” subscription) for your music in the settings menu. But be careful, higher quality settings consume more cellular data.

Personal experience

The best choice is really up to you and how you’ll play your music in your vehicle. Besides sound quality, you should also consider the ease of hook up and elegance of the connection. And given how noisy the car environment can be, you might not hear much of a difference between any of the connection options.

Tip: Try at least two different options with several of your favorite songs and see what sounds best in your situation. And the next time you install a new stereo, spend the extra couple of dollars to buy the extra cable to connect to the stereo's USB or auxiliary input. It's worth it in the long run.

What are the options for your vehicle?

Your options for playing your digital music through your car stereo depend on a combination of three things: The kind of vehicle, the stereo, and how you listen to your music. You can start the process by entering your vehicle info in our vehicle selector. If you need help figuring out the best option for you and your car, contact our advisors for expert advice. 

Last updated 6/16/2021
  • Greg Galetski from GREENWOOD VLG

    Posted on 6/24/2021

    Hi, I have SE200. I can listen music from TIDAL at home, but outside w/o WiFi I can't. Can you suggest something? Thanks Greg

  • Ken C. from Sugar grove

    Posted on 4/29/2021

    Explained very well , thank you. My favorite is aux line . Bluetooth streaming is not totally safe in high populated areas.. Love u all thank you.

  • John Akins from Richardson

    Posted on 12/24/2020

    I have a thumb drives with flac files loaded. Some of the source matierial is Hi-Res dowload or cd. Is this the best possible sound I can get? I can play the cds in my Kenwood Excelon radio, they sound as good as the thumb drive maybe a little better. Which should give the best response? I do have a Kenwood Excelon amp and Focal speakers

    Commenter image

    Alexander H. from Crutchfield

    on 12/28/2020

    John, if your Excelon receiver is able to play Hi-res files, then that's your best option (but CDs are a great source too). For more on Hi-res in the car, check out this article.
  • Vaibhav Chadha from Hong Kong

    Posted on 6/10/2020

    Hi I have a BMW X1 2019 model. The car has factory fitted headset and after marker match pp86amp and focal speakers. I use tidal premium subscription on my iPhone 11 to listen to music. The car has a usb c and regular usb input. My question is will a premium music player like aster and kernel give better result compared to iPhone 11? Also will adding a DAC to iPhone and then connecting to usb of car give better result?

    Commenter image

    Alexander H. from Crutchfield

    on 6/11/2020

    Vaibhav, the USB input is likely bypassing the benefit of a high-res player or external DAC to use whatever DAC BMX has built-in.
  • Dan Dennis from Annandale VA

    Posted on 4/15/2020

    Since I just bought and installed the Kenwood DDR9906XR (purchased from Cruchfield), it has Wifi Carplay, were do the number fall with Wifi, I would assume the same as Bluetooth, So far love the Kenwood DDX9906XR.

  • RICHARD A WOZNIAK from Saint Augustine

    Posted on 2/10/2020

    My 2020 Explorer doesn't have an AUX port. I have many CD's that I would like to play in the SUV. In the article Bluetooth and USB are stated as the best methods to connect to a car stereo. My problem, after several hours of searching, I can't find portable a Bluetooth CD player that will work with stereo nor can I find a USB cable that will attach either a Walkman or a DVD player to the USB connection in my SUV. You may not sell a solution but it would great to know if there is a solution. Thanks

  • andrew granovsky from los angeles

    Posted on 9/25/2019

    i have a 2017 mini cooper clubman with no cd player. I bought a portable cd player and tried using the aux cable to the aux in port and the sound was inferior to the radio. I next tried my cell phone music app over the aux cable with same result, however the phone over blue tooth was almost as good as the radio. Is converting the cd player to blue tooth the only solution and does anyone make such a converter ? thanks

    Commenter image

    Alexander H. from Crutchfield

    on 9/30/2019

    Andrew, if you can try a different cable for that AUX connection, that might be the best first step since a wired connection is going to give you better audio quality than wireless. If the AUX input is still sounding bad and you don't want to convert your CDs to digital files, then yes, it sounds like Bluetooth will be the only way to interface with that particular radio.
  • Dan from Addison

    Posted on 5/29/2019

    I have a 2018 Kia Stinger GT2 with the upgraded Harmon Kardon system. Have an iphone X with tidal app and have MQA listening capability. Is using the USB direct cable the best way to maximize audio quality or would a combination of Dragonfly Red Dac with camera adapter for iphone via the AUX input be better? I have no clue on how good the DAC is in the factory infotainment so I'm perplexed.

    Commenter image

    Alexander H. from Crutchfield

    on 5/31/2019

    Dan, great question. The Dragonfly/AUX option is the way to go. You won't benefit from MQA using the USB input.
  • Rob from Eagle Point

    Posted on 11/29/2018

    OK... so I know the typical frequency range for cassette tape read heads is in no way phenomenal but that is what I'm relegated to using and it seems like no one in the ENTIRE WORLD has done a review on a single cassette adapter. Having a terrible time finding ANY specs on ANY product. Seems like the current generation forgot what frequency range meant when it went digital and specs nowadays refer to color and size of product...ha Can anybody be so kind as to provide specs on the adapter transmission head of any product/adapter ??? Thx

    Commenter image

    Alexander H. from Crutchfield

    on 11/30/2018

    Rob, we don't carry cassette adapters anymore, but the frequency response of this Tascam cassette deck is 30-13,000 Hz (±4 dB). Hope that helps!
  • Marvin from Vollenhove

    Posted on 9/30/2018

    Is it possible to use a bluetooth receiver and connect it to the USB in on my pioneer DEH3800ui? to transmit digital audio via bluetooth (AAC or APTX with my iphone 8) and use the USB input while maybe even keeping the functionality like pause and skipping on the headunit?

    Commenter image

    Alexander Hrabe from Crutchfield

    on 10/1/2018

    Marvin, most of this will depend on the Bluetooth kit you choose. The more common adapter plugs into your aux input, and therefore you wouldn't have control of streaming from your head unit. You'd have to control playback from the source unit.