David,
I know you are an experienced musician (as a Taiko drummer) but just out of curiousity, Is Shamisen your first stringed instrument?
Well regrardless of that, Yes, there are indeed some tricks to keeping the Shamisen in tune.
I`ll share one that I use everyday before practicing, before concerts, between songs but especially after re-stringing.
First of all, find the pitch you wish to tune to. To give this a context let`s imagine the example of being on stage and just at the end of a song your string breaks. You rush backstage and frantically restring your Shamisen hoping to make it back out before the next song.You find the right pitch to tune to but unfortunately at this point thinking it will stay on the desired pitch will be about as frustrating as trying to float down a river in a boat with a gaping hole at the bottom.
So here`s what I do to quickly overcome the problem.
follow these steps…
1.)First secure the string in place firmly and tune it to the right pitch.
2.) Next stretch the string out (this will force it out of tune again).
3.) repeat this process over and over. (stretch it out of tune, tune it, stretch it
out of tune, tune it). At a certain point you will discover that stretching the string
no longer has the effect of knocking it out of tune.
At this point your Shamisen has stabalized and you can safely return to the stage
or jam session free of stress from tuning problems.