UAC1 DAC (ODAC): digital vs analog output

Question

I am trying to get Ubuntu to output I2S output to my ODAC. When I go into sound settings, I get two options.

• Digital Output (S/PDIF) (IEC958, so it must actually mean S/PDIF...)
• Analogue Output (This is the one I am confused about)

From what I know, a DAC converts digital signal to analogue. I also know that the ODAC supports I2S.

The question I have is, which do I have to select to get I2S output via USB? I know that the ODAC does NOT support S/PDIF so it is very strange to see it there. Is Ubuntu displaying I2S as S/PDIF incorrectly? Or does the Analogue Output actually mean I2S? Or would selecting the Analogue Output process the sound through my laptop's DAC and bypass the external DAC?

Any help would be greatly appreciated. Thanks!

Solution

As discussed in What does USB DAC "Analog Output" mean?, I suspect that Analog Output means that the OS will first pass the digital stream to the inbuilt, computer DAC device (i.e. sound card), and then the analog stream will be passed on to the USB device for amplification and further to your headphones/speakers. The improvement in quality (versus the computer DAC) will be minimal, and will come only from the external DAC amplifier.

Digital Output means tha the OS fiddles not with the digital stream and passes it directly to the external DAC device for conversion to analog, amplification, and then to your headphones/speakers. The quality should be much better, and will depend on the quality of the external DAC (since the inbuilt DAC will be completely bypassed).

So for best quality you would choose the Digital Output port.

See also:

• How can I enable digital output on a FiiO E7 without ending session?.

Comments

[CL.]

I²S is a protocol different from USB. If your device is connected through USB, it is not possible for the laptop's built-in DAC to affect it.

[Michael Yoo]

@CL. I see. Which one should I be using(which one has a better quality with an external DAC, if they have any difference at all)? From what I've researched the only difference is whether timing information is included or not.

[CL.]

You always use USB. These outputs (if they belong to that DAC at all) are for the digital and analog outputs of that DAC, i.e., they specify where the sound is routed after it has been transported to the DAC over USB.

[Admin]

gitlab.freedesktop.org/pipewire/pipewire/-/wikis/…

[CodingInCircles]

I have a Dragonfly AudioQuest DAC. When I use it on Ubutu and select Analog Output, it sounds louder at a lower volume. Selecting Digital Output seems to make it just as clear, but not as loud. Why is this? What are the recommended settings?

[Admin]

@codingincircles sounds louder but the detail on the sound is much higher when I do digital output instead of analog output with my Fiio BTR5.