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I have the following hardware:

The dock has a 3.5mm headphone port. It appears as "Realtek USB2.0 Audio" in the MacBook's Sound menu.

I think the headphones sound different when plugged into the dock compared to the MacBook. I'm not an expert, and it's hard to compare. The sound seems slightly thinner and less rich.

I imagine the dock has its own DAC, causing the sound difference. My question is, can I send the MacBook's analog signal through the dock and use its headphone port, without plugging anything directly into the MacBook?

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  • Without some research, I'd say out of hand there's no way to reroute the audio. The Satechi is pulling the AV data from the TBolt 4 connection as you surmise, and its internal DAC (Realtek) is the extracting the audio to the headphone jack. The Realtek USB2.0 Audio is actually, from what I can gather, a generic sound processor. Most, if not all, of the links I found referenced Windows as the primary OS where Realtek is used.
    – IconDaemon
    Commented Jan 22 at 22:30
  • Thunderbolt 4 doesn’t have dedicated audio channels - audio comes from the Displayport signal. However since the 3.5mm port is a mic/headphone port, it’s likely a USB audio device (cost). For the record, the Mac’s built in DAC is mediocre at best
    – Allan
    Commented Feb 26 at 3:30

2 Answers 2

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There's no analogue path from the Mac to the Dock, so the headphone jack can only be used from the dock's internal DAC.

You're only viable alternatives are to plug directly into the Mac, or buy a better USB2 DAC you can hang off the dock.

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The USB-C port does offer the means to support both audio output and Thunderbolt, as should any Apple product with USB-C made in the last five years, just not at the same time. I know Wikipedia isn't always a trusted source but it is convenient, they can show how the two output modes interfere: https://en.wikipedia.org/wiki/USB-C#USB-C_receptacle_pin_usage_in_different_modes

A summary of the issue is that to get into audio accessory mode the CC pins are shorted to ground and to get into Thunderbolt mode the dock has to communicate this by serial communications on the CC pins, the two modes are mutually exclusive. There cannot be this serial communications required for Thunderbolt with the CC pins shorted to ground for audio accessory mode. Further, the audio accessory mode repurposed the USB 2.0 pins for analog audio which could make support of docks that rely on the presence of the USB 2.0 data for features difficult.

There's a potential for exploiting some alternate modes on USB-C to offer Thunderbolt and analog audio at the same time but the host computer and dock would have to support this. Maybe, possibly, perhaps, Apple could make this happen with some kind of software and/or firmware update in the future, it all depends on how pliable the hardware is to get into such a mode. Then is the matter of the dock supporting the same manner of getting analog audio and Thunderbolt on the same cable at the same time.

While I can imagine ways to allow analog audio and Thunderbolt on USB-C at the same time I have my doubts it will happen. First is that there's not likely much demand for such a feature, it's likely cheaper and more convenient to put a USB 2.0 audio DAC in the dock than run the wires for analog audio. Then is the matter of demand, without enough people expressing a desire for such a feature it is unlikely any hardware manufacturer will put in the effort to support it.

What I would suggest is find an alternative USB DAC to plug into the dock for better audio quality. Of course there's the option to use the DAC in the Mac but it sounds like you'd rather not out of convenience. If this is important enough to you then I see a resolution, it's just a matter of how much you are willing to spend to gain this convenience and audio quality.

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