[sdiy] Digital Modules

[Busby Bergson]

Hi there, DIYers -

I apologize if this is the wrong forum for this, but I've been curious
about the rise of digital modules among modular synthesists.  I have a
lot of very introductory questions, but I haven't managed to find an
introduction to this stuff anywhere (does one exist?)...

Are there standard DAC/ADCs that get used? If so, what are they? Or do
people usually design their own?
Are there simple "shields", such as in the microcontroller world, that
handle basic digital audio processing? It seems like a Raspberry Pi
would be able to do a bunch of this stuff out-of-the-box - but I'm not
sure it is a real industry standard..
If people here do this kind of work, what sorts of programming
languages do you use?

Thanks,
BB