What does USB DAC "Analog Output" mean?

Question

I just connected my new Rega DAC to the computer via USB, it popped up in the sound settings, and choosing it there directs sound to it just fine. What confuses me, however, is that it says "Analog Output". What does that mean in this context? I suppose the output must really be digital, since it works when it's connected to the digital input on the DAC, right?

Sorry if this is a stupid newbie question, I'm very far from an expert on Linux audio stuff, but I'm going to start learning, so I hope you can help me.

By the way, do I understand correctly that what I am communicating with in the sound settings is the ALSA layer?

Solution 1

Everything on USB is digital. "Analog Output" describes the output of the DAC.

Ubuntu's sound settings are the PulseAudio layer.

Solution 2

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).

See also:

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

Comments

[Raphael Roth]

And why can I change the volume within Ubuntu although I have Digital Output selected (using Fiio Olympus 2)?

[Bas Swinckels]

stupid question, but how can an analog signal from the in-built DAC be sent over USB to the external device?

[marcan]

This is wrong. There is no such thing as "passing the digital stream to the computer sound card and then having the analog output go to USB". USB is always digital, and built-in sound cards have no mechanism to route stuff through USB (except on certain phones/tables/embedded devices that might support analog alternate modes over USB Type C or in rare legacy devices microB, but that wouldn't show up as a USB device in something like PA, it would show up as just one extra mode of the embedded card/DAC itself). The other answer is right.