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How does audio from iPhone get to head unit over USB?

4.3K views 33 replies 9 participants last post by  dumdum  
#1 ·
Hear me out. My car's factory stereo doesn't have wireless audio features.

When I plug my iPhone into my car's usb jack that is in turn connected to the factory head unit, I get audio and all the data like song, artist, cover art, etc on the display and audio through the speakers.

And it's not just specifically "my car". I drive various makes and models at work and they all work the same way when plugging my phone in the usb port.

What codec(?) is it using to transmits the data and audio over that usb connection to the stereo?


Ok, I'm asking because I want to know if there is a device that looks like a usb thumb drive, that accepts a wireless audio signal (AirPlay, Bluetooth, whatever) from my iphone and sends that signal/data to the stereo through that same usb jack as if the phone were connected with the usb cable.

I realize such a scenario may involve some conversion of the audio signal and possible degradation. Looking for the least lossy conversion.

Thanks!
 
#5 ·
I could 1000% wrong, but I think the first thing to figure out is what the nature of the signal going through that usb cable is. Whether its an iPhone or android phone. And these cars are older and I don’t think they have wired CarPlay, which is what I think these devices need.
 
#4 ·
Hmmm? So these cars at work are like 2016 and 2017 models. I don’t think they have “wired” CarPlay. The factory stereos are pretty plain Jane. So this will still work? I’m reading this on one of the ads…
“As long as your car is built with factory wired CarPlay,”
 
#6 ·
If your getting the music and track info etc over USB, sounds like it's still CarPlay. It's been around since 2014 in various vehicles. Here's a more in-depth explanation of how carplay works:

 
#9 ·
Wired CarPlay / USB audio will get you the best possible audio stream from your phone. It’s a PCM stream so bit perfect. Wifi CarPlay is transcoded into acc-lc which is a lossy codec. However, CarPlay wifi is better than classic Bluetooth A2DP for streaming.
 
#11 ·
Gotcha. I want to maintain some level of quality but I need more convenience! All this plugging/unplugging all day is too much. Lol.
Oddly enough, the Tahoe has a 3.5mm aux jack, but it sounds terrible. I bought one of those screens that has wireless CarPlay that I figured would fix my issue, but it plugs into the 3.5mm aux jack and the audio is as bad as when I use a headphone adapter on the phone and go straight 3.5mm into that jack. I would’ve assumed that would have been the highest quality signal.
This is why I decided to go the USB route. Audio is great from phone through USB.
 
#12 ·
Thanks for the topic, I just bought the one linked below, it has the highest rating of all devices and is on sale for $53 ..

Wireless CarPlay Adapter, CarPlay Dongle for OEM Wired CarPlay Cars, Convert Wired to Wireless CarPlay, Support Online Update Plug & Play Easy Use Fit for Cars from 2015 & iPhone
 
#29 ·
Have you received it and tried it yet? Mine came in and plugging it into the usb port on the 2017 Tahoe that likely only has “iPod integration”. The light on the device comes on but it doesn’t show up on my iPhone 15 as a Bluetooth source so that’s a dead end. I’m going to try it in my personal car that has a pioneer HU they has wired CarPlay to see if that connection somehow triggers the unit into showing up as a Bluetooth device on my iPhone.
 
#13 ·
Gotcha. I want to maintain some level of quality but I need more convenience! All this plugging/unplugging all day is too much. Lol.
Oddly enough, the Tahoe has a 3.5mm aux jack, but it sounds terrible. I bought one of those screens that has wireless CarPlay that I figured would fix my issue, but it plugs into the 3.5mm aux jack and the audio is as bad as when I use a headphone adapter on the phone and go straight 3.5mm into that jack. I would’ve assumed that would have been the highest quality signal.
Thanks for the topic, I just bought the one linked below, it has the highest rating of all devices and is on sale for $53 ..

Wireless CarPlay Adapter, CarPlay Dongle for OEM Wired CarPlay Cars, Convert Wired to Wireless CarPlay, Support Online Update Plug & Play Easy Use Fit for Cars from 2015 & iPhone
I guess we’re both about to find out…I ordered it too 🤣👌🏼
 
#14 ·
If it's not CarPlay, it's iPod integration.

Even though iPods no longer exist, iPhones still act like one when plugged into a iPod compatible device.
 
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#24 ·
I got all excited about wireless carplay and bluetooth audio. Then realized I had to plug in my phone to charge it anyway. Now using wired carplay. Before that used a dragonfly to 3.5 to aux input. The dragonfly dac made a huge difference in sound quality. This is with iphone by the way
 
#25 ·
Difference is with wireless CarPlay for someone getting in and out of the car several times, you can plug in to charge only when you want/need to but still listen to music etc. With wired CarPlay I’m constantly plugging/unplugged at each destination throughout the day. Not fun. It’s even more convenient to plug phone into portable battery if you have wireless CarPlay if getting in and out of the car frequently.
I find wired CarPlay is only not inconvenient on longer trips.
 
#26 ·
We sure get addicted to technology. I remember when we had to eject a cassette to turn it over. Then came auto reverse.
 
#28 ·
Just changed out my factory headunit with a later one that supports CarPlay . Didn’t realise it was wifi audio only and can’t force audio to standard USB to get bit perfect.

One step forward, one step back. But at least all the iPhone apps are control via factory interface now.