Hi Nir,
This mode is used with applications such as FT8 and WJST-X (which is an external program).
I currently run WJST-X routinely and yes you have to run in Digital mode. ?The RPi sound card is used and it works well for me. ?I¡¯d like to run JS8Call but I¡¯ve not been able to make that work.
Others will have more technical descriptions but that¡¯s what it¡¯s for.
Cheers, Scott