I stopped using Bluetooth audio in my car, and my music finally sounds like it should

Personal audio can be a bottomless pit of money and wants, but few people realize cars are the perfect place to settle in for a calm listening session. They're well isolated from ambient noise, speakers are typically set up in a classic surround-sound layout like a home theater, and you can stream anything from your library to the vehicle's infotainment system with conveniences like Android Auto and Apple CarPlay.

Unfortunately, carmakers and smartphone brands work together to push Bluetooth audio and wireless device connection as a lifestyle choice you shouldn't ignore. Sure, it is frictionless and easy to set up in five minutes, but the connection fundamentally lacks quality, shredding the audio stream with compression, basic codecs, and the limitations of the Bluetooth protocols involved.

The audio suffers even if you're using Wireless Android Auto on a supported car or through an aftermarket dongle. I caught on to this early, weighed my priorities, and found that ditching wireless audio in the car might be just what the doctor ordered if you're a car-loving audiophile with exacting quality standards.

Wireless audio is fraught with limitations

A wired connection is, too, but it's the lesser evil

Using Bluetooth to connect to your car's infotainment system is the epitome of convenience. Like keyless entry, push-button start, and an automatic transmission, setting up Android Auto to start as soon as your phone is within range and the vehicle powers on feels like a superpower. The novelty doesn't wear out quickly either, with conveniences like wireless call controls and voice assistant instructions ensuring this gift keeps on giving. Unfortunately, I've also found that most vehicles build this feature as a necessity more than a thoughtful addition.

Except for flagship automobiles, most brands don't advertise the Bluetooth version shipped in their vehicle's hardware. Even if you're running an aftermarket headunit to smartify an older car, you'll notice they ship with older Bluetooth standard and limited support for high-res codecs, defaulting to lossy, highly compressed streams like SBC and AAC codecs. This doesn't seem problematic to the average listener, but some of us can tell CD-quality audio stored in FLAC files apart from highly compressed formats like MP3 and their equivalents used by streaming services.

Before I get into the technicalities, it's worth noting that most compressed audio streams playable on your phone or stored on a USB drive are encoded for two-channel stereo playback, and not surround sound. Yes, your car's speakers envelop you perfectly, but they're still playing back two-channel audio relayed to the amplifier through your playback device.

This doesn't change whether you're using a Bluetooth connection or a cable with 3.5mm TRS/TRRS termination. The number of connectors and conductors limits the cable's transmission capabilities, while the Bluetooth standard limits wireless transmission, with Spatial Audio as the only widely recognized exception. For a wired USB-C connection like Android Auto, audio transmission defaults to the highest supported common standard, which is typically a two-channel affair.

Why is Bluetooth substandard for audio transmission?

Bandwidth, surprisingly, isn't the biggest roadblock

With the channel limitation out of the way, we can focus on the Bluetooth standards. The latest commercially available ones, designated 5.0 and 6.0 by the Bluetooth Special Interest Group (SIG) can transfer data at up to 2Mbps on the BLE protocol (LE 2M PHY) we see deployed in wearables to sip power. On the classic Bluetooth (EDR) where power draw isn't a concern, streams top out at 3 Mbps. However, after accounting for protocol overhead, packet error correction, and RF stability buffers, the practical limit for audio streaming is 1.1 to 1.2 Mbps. You'll find this used by most wireless Android Auto dongles, CarPlay, and vehicles with Android Automotive built in.

That's the data rate needed for uncompressed, CD-quality audio at 16-bit depth and a 44.1kHz sampling rate. Proprietary codecs like Qualcomm's AptX Lossless (aptX LL) support such audio streams, but it's typically a two-way handshake that requires codec support on both the streaming phone and the receiving vehicle. The latter typically lacks support, and moreover, aptX LL is a dynamic codec that scales down to lossy compression under suboptimal RF conditions. Other well-known high-quality Bluetooth audio codecs such as LHDC and Sony's LDAC stay under the 990kbps data rate using lossy compression on up to 24-bit/192kHz audio.

To the listener, this just means you'll have a hard time transferring the audio in all its glory from your player to your vehicle on a wireless connection. Matters get even worse if either hardware stack in this exchange lacks hi-fi codec support. Then, the default is typically legacy codecs like SBC, capped at 328 kbps. You'll find this used on most cars, aftermarket head units, Bluetooth receivers, and Android Auto/Apple CarPlay adapters. Unfortunately, not every customer is an audiophile, and most users only care that their navigation instructions blare through the car speakers when connected.

As such, a truly lossless and uncompressed audio stream at 24-bit / 192 kHz is only feasible on a wired Android Auto connection or wired Aux since it can demand up to 9.2 Mbps of data bandwidth.

Wired connections are superior

And immunity from packet loss is the smallest win

In our testing, a wired Android Auto connection defaulted to the PCM codec, seen on the Android Auto settings page under Developer Options > Audio Codec. That also surpasses the audio quality of other available options, such as AAC-LC. On your smartphone, you're streaming service first decodes audio into raw frames and pushes it to the Android audio engine, a service known as AudioFlinger.

It resamples CD-quality 44.1 kHz input to 48 kHz at the same 16-bit depth, but will dither Hi-Res 96 kHz / 24-bit or 192 kHz / 24-bit tracks down to 48 kHz / 16-bit LPCM. The Android projection service then splits media audio, navigation instructions, and voice calls or system sounds like Gemini, so one can take priority over the others, as required.

This audio signal only requires around 1.54 Mbps of the 12–18 Mbps total data footprint of an active wired Android Auto connection. The vehicle's digital signal processor (DSP) handles subsequent processing, including cabin equalizer, fader and balance trim, and delay sync, before sending it to the digital-to-analog converter (DAC) for playback through speakers.

In this exchange, the wired connection for Android Auto removes codec-compatibility bottlenecks, drastically improving and standardizing sound quality. You could also achieve similar results using a dongle DAC connected to the phone, paired with a male-to-male Aux cable for older vehicles.

A little inconvenience might be worthwhile

If poor audio quality is bothersome enough that you've read this far, chances are you won't find a wired connection too inconvenient a solution either. Sure, it adds friction in the connection process and contributes to disproportionate physical wear and tear of your phone's USB-C port. If you value audio quality enough, you'll also enable all EQ and processing on the phone and have the car's EQ play it back with as little intervention as possible.