Digital communication has a wholly different set of requirements than audio processing. With audio it is good enough to sound good, but digital communication has far more specific metrics of performance.
Digital communication is also far more structured, which makes it possible to implement a large number of techniques for improving signal quality.
Almost all digital communication systems would have something along: adaptive equalization, carrier tracking, symbol clock tracking, forward error correction, and many, many more techniques.
I agree that the technical requirements for transmission are very different than in a professional audio context. What I meant is that, once the signal has been acquired, there could be some additional processing to make it "sound better" (is: increase speech legibility), independently from the transport method.
I’ve only learned about this through my engineering studies, so I can only really recommend textbooks. I found Proakis’ Digital Communication quite good, but it doesn’t go very deep.
I don’t know of any online resources – but I’d love to have the time to write some signal processing for communication is fascinating and has a wide impact on everyday life.
Also wrt. implementations: I think GNU Radio might be a good place to look, but honestly the actual implementation of these algorithms is often very simple, it is the theory behind them that gets hairy.
Digital communication is also far more structured, which makes it possible to implement a large number of techniques for improving signal quality.
Almost all digital communication systems would have something along: adaptive equalization, carrier tracking, symbol clock tracking, forward error correction, and many, many more techniques.