I loved that they had to do everything live. Lip sync ruined everything. Morrison had a good voice but he was a total lop of a person, IMO. He would have never grown up.
JM was a big fan of Frank Sinatra and certainly had that "smooth, crooner voice" at times.
He also knew FS used a Neumann U47 microphone that used a German Telefunken vacuum tube.
It was THE most transparent mic to clearly capture vocals and still remains a legend in studios and was ecstatic.
When the Doors walked into Sunset Recording Studio, JM immediately saw a Neumann U47 microphone that would be used for his vocals.