Hi Res Audio Playback

  1. txtx

    txtx Member

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    #16 txtx, Feb 10, 2019
    Last edited: Feb 10, 2019
    I have been connecting an iPhone through the front USB port to avoid the Bluetoofs.

    I meant digital audio players (DAPs, an Onkyo DP-X1A as an example), not a phone or an iPod. DAPs are mostly Android-based, and I'd like to know if anyone has had direct experience with a Honda rejecting one, treating it like a USB drive, accepting whatever it plays or only through Android Auto.

    I believe the head unit must convert to analog, since the signal is all digital until it comes out of the speakers.

    The head unit also accepts lossless WAV files through a USB drive (16-bit/44.1khz anyway).
     
  2. daPyr0x

    daPyr0x Senior Member

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    #17 daPyr0x, Feb 10, 2019
    Last edited: Feb 10, 2019
    As much as it would seemingly make sense that connecting over usb would avoid bluetooth, both carplay and android auto use bluetooth for audio. the usb is only used for video and controls data.

    I don't have direct experience here, but I can tell you with relative certainty that connecting one of these devices to the USB port in your car would give you the equivalent of plugging a USB flash device containing the same files. It is conceivable to create a device that could transcode on the fly to WAV files that it presents to the HU, but that still wouldn't give you anything more hi-res than encoding to WMA-Lossless and putting that on a static USB flash drive for a lot less money.

    There is no way to pass analog audio data over USB to the Honda HU, which is what you would need to do to take advantage of the Hi-res audio support and high-quality DAC features of the devices you describe. It only accepts digital data. Your best case with a device like these would be a HU with an analog input that you can connect to via the headphone jack or other form of line-out. I am not aware of any way to do this with the stock HU with the exception of some aftermarket amplifiers that provide their own line-in option.

    You are correct, the HU does convert to analog. Your phone decodes compressed music (ALAC, MP3, ogg, etc) to an uncompressed state (wav, effectively) and then passes it to the bluetooth chip who recompresses it using lossy compression (possibly even back to mp3) for transmission to the reciever (car HU). The receiever then decodes back to an uncompressed state and passes on to the DAC where it becomes an analog signal for the amplifier and speakers
     
  3. kg4fxg

    kg4fxg Senior Member

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    Well, that explains why I see so many wearing ear buds. At first you could have one ear bud in your ear. Then came the hands free law in GA. Cell phone can't be buy your ear and no texting while driving. But yet I see folks with two ear buds in. Actually saw one guy wearing a pair of headphones. Certainly a simple fix to crappy car audio. Illegal I assume. Too dangerous to me as I could not hear anything outside such as emergency vehicles.

    BTW, I use Shure SE846. Sound isolating and very good in ear for the audiophile. And no the car audio does not compare to it. Almost impossible to see as they tuck behind your ears such as musicians use on stage.
     
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    fabrizzio71

    fabrizzio71 Member

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    I have looked for some sort of technical paper from Apple confirming exactly how audio is transferred with CarPlay, but I haven’t been able to find anything conclusive. Would you mind sharing if you have a source that confirms this? If accurate, that is frustrating indeed, as it means all the time I put into converting Hi Res files to ALAC thinking I could get Hi Res off my phone was for nothing.
     
  5. daPyr0x

    daPyr0x Senior Member

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    Well, I did some more research and I found a link that proves me wrong. My previous research was Android-focused as I am not an iPhone user. All the same - see here. The presentation describes that when connected via USB, uncompressed PCM audio is sent over the USB connection. When connected wirelessly (not supported by any Hondas I'm aware of), compressed audio (AAC-LC) is sent over Wi-Fi.

    All that is to say, losslessly encoded 16/44.1khz files will play losslessly via wired Carplay. I was incorrect in my previous statements, they are only accurate for Android Auto.
     
  6. txtx

    txtx Member

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    #21 txtx, Feb 11, 2019
    Last edited: Feb 11, 2019
    I found that presentation as well, and the below screenshot was the most conclusive to me.

    From TechRadar 7/2018 about Android Auto...
    "Audio is sent to the car’s speakers via USB for music with no reduction in sound quality, unlike with Bluetooth audio streaming. Phone calls are handled via Bluetooth hands-free."

    For what they're worth, multiple AA forum posters state the same (audio over USB if you untick Media Usage in BT settings) and the audio sent is PCM 16-bit/44.1k.

    Screen Shot 2019-02-11 at 1.05.29 AM.png
     
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