Not what you call new to renoise but I’ve never been able to find the existence of a command that plays a note twice for one tick.
Basically as if you had expanded your track and doubled the bpm and filled the empty space.
Like so:
Position - note
0 c
1 c
c
2 c
3 c
4 c
Why not just do that? Because I don’t like having huge blocks at super fast tempo. I just occasionally want to add this effect.
Retrigger command?
http://tutorials.renoise.com/Renoise/EffectCommands
# 0exy - Retrig notes in track-row every xy ticks (y=ticks 0 - ticks) The first digit (x) sets the volume of the retriggered sample. Value effects on volume for each retrig are (x):
* 0 No change
* 1 −1
* 2 −2
* 3 −4
* 4 −8
* 5 −16
* 6 *2/3
* 7 *1/2
* 8 No change
* 9 +1
* a +2
* b +4
* c +8
* d +16
* e *3/2
* f *2
That’s the one. Cheers. I’d read that but didn’t really understand it.
No probs 
that leads me to another question:
what about the good old pattern expansion?
(it was an option in ft2 which doubled the length of the pattern, e.g.:
c-1
c-1
c-1
i found this very usefull in old days 8)
aah, thank you! found out that i have to mark the range which should be expanded, works fine 8)
if you want to expand the whole pattern, choose “whole pattern” radio button at the top of the panel