Crosby, though it seems an odd idea now, was a revolutionary singer.

First, he realized that he was singing to a microphone, so he shaped his technique around the strengths and limitations of the microphone(he also introduced the tape recorders to broadcasting and pioneered in editing as we do it today), Second, and even more important, he developed a conversational/confidential singing style--instead of singing as if he was performing for a theatre full of people, he sang as if he was singing to just one person--which changed everything, forever after....