[SOLVED] Anyone explain this to me please?

[Nutul]

Yes. Thats what it means. Linux audio provides low level access to device options such as on-chip or on-board volume controllers.

There are other options in moOde for physical volume controllers for example Rotary Encoder or USB Volume Knob.

I am curious... now, what is the actual difference between Hardware (or, like it writes on my machine, Null) and Fixed (0dB output)?

Audio Config "Volume type"

Hardware: MPD requests audio device on-board volume controller to perform volume calculation.
[b]Software: [/b]Perform volume calculation using MPD software volume algorithm.
Fixed (0dB): MPD outputs 100% (0dB) volume level. This corresponds to MPD mixer_type "none".
https://mpd.readthedocs.io/en/latest/use...io-outputs
Null: MPD creates a fake mixer. This is useful for implementing an external volume control.
https://mpd.readthedocs.io/en/latest/use...rnal-mixer

Note that "on-board" volume controllers can be implemented in the DAC chip itself or in the USB chip. Which one is used depends on implementation.

For example in some implementations where the volume controller on the DAC chip is superior to the one on the USB chip the USB chip is programmed to proxy volume commands to the volume controller on DAC chip. This would be something like a DAC with an XMOS USB chip and an ESS DAC chip with its "Hyperstream" volume controller.

I understand that all of these volume paths remain in the digital domain, so having the 100% / 0dB output no matter how, is the way to go for an analog volume.

I do not see Hardware as an option in my settings (maybe this applies only for the HATs, don't know), just Software, Fixed and Null. So far I have always used Software, but the volume reel in moOde has always been left at the maximum, hence I assume it has always been as if I had chosen Fixed (0dB), right?

P.S.
The links to the MPD documentation lead both to a 404 redirected page ;-)