| I used to be great at trills on my guitar... then I switched to bass. I can still do it, but I got a lot worse. Can't bass tap (the normal way) either. I do, however, have an exercise I think I could help. It's really simple, so don't rely just on this, but you could do it all over the neck.
Basically, using the one-finger-per-fret method, pick any fret, fret it with your first finger, then strum. Pull off, and without picking at all (for the rest of the exercise) hammer on to the next fret, then pull of and go back to the first, pull off to the third, etc. Your fingers should go something like 1-2-1-3-1-2-1-4-1-2-1-3-1-4 etc.
In tab, it might look like:
G: -9p-h10p-h9p-h11p-h9p-h10p-h9p-h12
Just do that. Slowly at first if you want. It helps with your hammer ons and pull offs, but maybe not so much for a trill. Just work your way up to trills (two hand tapping if you want) from here.
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Ibanez BTB club # 152
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