Moving dynamic markings & changing font weight

[Geoff Horton]

I found a post on the list which suggests using the staff-padding
parameter to put all dynamic markings on the same baseline. But it
didn't say, and I can't figure out, how to actually make that happen.
Based on the manual, this parameter belongs to TextSpanner, which
lives in Voice, so

\layout {
  \context {
    \Voice
    \override TextSpanner #'staff-padding = #10
    etc....

looks like it ought to do the trick (and more--the enormous padding is
there so I could make sure any effect would be obvious). It doesn't.

Likewise, I'm trying to change the font weight for dynamics from bold
to medium. This belongs to DynamicText, which also lives in Voice, and
  \Voice
  \override DynamicText #'font-size = #-2

does work to shrink it, so I'm in the right ballpark. But
  \override DynamicText #'font-series = #'medium
does nothing.

What am I missing?

Geoff