Searched the manual for this and came up empty. I think most of us know it's for data modes, but what exactly does it do?

I'm playing with FreeDV currently and in addition to running 14.236 USB-D i also have the Noise blanker, Notch filter and Noise reduction disabled.

I'm kinda wondering what the point of the -D mode is. Also I've had a look at the preset menu to see what functionality it brings. Potentially a few hand things there like ability to set different addresses, baud rates etc..

But neither -D mode or the presets disable the NB, NF or NR, thus when switching between voice and data modes these always have to be toggled... Leaving me wondering the point of -D is or the point of the presets?

Unless I'm missing something the vast majority of the digital modes prefer the most direct audio with minimal molestation (blankers, filters etc).

Have i got a point here or am i missing something? What does the -D mode do?