Unexpected Resampling in ARC

Roon Core Machine

Model: Shuttle XH110

Intel(R) Core™ i5-7400 CPU @ 3.00GHz

RAM 8.00 GB

Windows 10 Pro 64bit

Networking Gear & Setup Details

Router: Orbi Pro SXR80, matrix with SXS80 Satellite
Core: wired gigabit Ethernet
Internet: AT&T Fiber (gigabit up and down)

Connected Audio Devices

iPhone 13 Pro Max, iOS 16.0

Alpine ILX-207, USB CarPlay

Number of Tracks in Library

~20K locally

~5K on Tidal

Description of Issue

Just wanted to report some unexpected behavior with resampling in the ARC app while connected to my car head unit via USB. Some may be by design, some not:

My Alpine ILX-207 head unit is listed as being compatible with both 48kHz and 44.1kHz sample rates, but when I set ARC to “original format” and listen to 48kHz tracks (e.g., MQA files from Tidal), it does a sample rate conversion to 44.1:

Maybe it does this because ARC isn’t sure about the Alpine’s ability to handle 48kHz? Or the Alpine actually transcodes 48 to 44.1 and Roon somehow recognizes this and does the transcoding beforehand?

Either way, I tried setting ARC to “CD quality” in hopes it would just request the redbook version from Tidal, but then I see this:

That can’t be right? Can it?

It’s likely using the iOS iPod/iPhone dock protocol to connect and not as a full USB DAC old iPod connection only supported 44.1. What ever arc will only use what it gets back from iOS as to what it supports in this case 44.1/24 by the looks of it.

Do you have 3.5mm auxillary in with your car system? Try using an attached DAC with that and you should get up to 24/192. If you car system can only accept 44.1 or 48, you won’t notice any difference.

Thanks, but this defeats the whole car audio interface (steering wheel controls, big touchscreen display, handsfree calling, etc.)

Then, you’ll have to live with 44.1. I can’t connect to Roon ARC right now, but IIRC, that’s what the iPhone does without an external DAC.

Oddly enough, every reference I can find to Carplay’s standard is that it supports 16/44.1 or 16/48. And the specs for the head unit claim to support 48kHz. So maybe I have something wrong in the settings so it is using the old iPod dock protocol instead of the Carplay audio pipe. Even so, that doesn’t explain the resampling a 44.1 file to 44.1.

The iPhone without an external DAC resamples everything to 48. And people have been griping for what seems like decades about Airplay and AppleTV resampling everything to 48, so it would be surprising if Carplay doesn’t support 48. That said, I’m fine with 44.1, but I’m not thrilled about resampling 48kHz files to 44.1 when the 44.1 file is right there.

What do you see if you just play to your iPhone speakers? Maybe your car head unit is doing this??

CarPlay isn’t really supported yet as arc has not had anything coded specific for it. It’s luck it works at all so likely this is part of the reason.

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