Start - 1986: The unmistakable DS voice
1991 - 1992: Bored, tired, effortless
1996 - 2005: Same darkness as 91/92 but with far more effort and joy
2006 - 2010: Favorite solo era, had to keep up with Emmylou's beautiful singing, especially singing marvelous on the KTGC tour!
2011 - 2015: Mix between 1996-2010 era's
I found his singing on Tracker generally weak, but it suited the record. Of course, I still love the sound of his voice, but all power and urgency faded away. On DTRW, it's not a style/choice anymore. The need to deliver is gone. I think you can even hear which songs were recorded at the beginning of the session and the ones later on, closer to the release. Is he even trying on Heavy Up? You can also hear it on the latest tour, for example, in R&J, which always had passion and urgency, but it's completely gone.