Well, I've used Deeaa (or originally just D/A) for aeons already...way back in high school I was kind of a class clown and I was so full of seriously dry jokes that made people laugh mainly because they were so bad, some people started calling me 'Dry Antti'.
When I started my first real gigging band in '88 or so, I had to mark all the cables and stuff to tell them apart from the other guys' gear, and I started marking all my stuff with 'D/A' which seemed a handy sig.
It just went from there, pretty soon I had labeled everything with D/A from guitars to cables...and the last affirmation, when I was in the U.S. and told everyone my name is Antti Heikkinen, nobody could pronounce it even close; people actually thought it has no vowels in it at all and thought it was written like 'N'Tk Hk'knk' or something, but it's pronounced more like 'Unt-tee- Heyick-in-en'...
Well anyway I got frustrated with the various styles of pronouncing it and as I had every luggage etc. labeled D/A, it just turned to people calling me 'Dee' which stuck as a name to be used for English-language productions.
I went on to put up a production 'company' called Digital/Analog Productions, i.e. D/A productions, and produced a handful of CD releases under it, and then even had a band called D/A later...
So there you have it...that's why I use 'Dee' in speech in English and 'Deeaa' as my nick - it's simply how you say D/A in Finnish.
Sometimes I've used Deeaa as my pseudonym also in videos, band credits etc. but lately I usually use "Antti 'Dee' Heikkinen" or just Dee.