Dynamics and kerning

[Kim Bastin]

I find the kerning of dynamics unsatisfactory, indeed I'm not sure that 
it's happening at all. ff is spaced too wide, with visible daylight 
between the f's; mp is squashed too close together. These pairs are the 
worst; pp, sf, fz look okay.

Is this a characteristic of the font? If so, is there a way of changing 
the default dynamics font?

Or has it got something to do with this statement in the user manual, 
1.8.2.1:

"Kerning or generation of ligatures is only done when the TeX backend is 
used. In this case, LilyPond does not account for them so texts will be 
spaced slightly too wide."

How does one "use the TeX backend", assuming that's the problem? As is 
no doubt obvious, I understand very little of this.

[Lilypond 2.11.45, WinXP]