Sometimes what is obvious to a few has been unquestioned by many others. Here’s a great example from an inSync reader.
“I have a question that came up when thinking about D/A converters. I was thinking that if one needs a D/A converter when mixing and recording etc. how have my digital keyboards functioned over the years plugged into an analog board? Is there a converter in the instrument?”
Yes. D/A conversion has been in instruments dating all the way back to the Korg M1, Kurzweil K250, and Roland D50. As soon as people starting using PCM ROM sounds in their instruments (as opposed to synthesizing them on the fly) it became necessary to have D/A converters on board.