I'm a harpsichordist. The harpsichord is a keyboard instrument that was common from about 1500 to 1800. It has a very light keyboard compared to the modern piano that doesn't require much strength or force to push down. It's almost like typing on a computer keyboard. All movement going into pushing the keys down is relegated to the fingers whereas in piano technique, the arms and back are involved somewhat since the keys are much heavier.
Music for the harpsichord is usually filled with these little short but fast melodic figures known as ornaments that decorate the music. Most ornaments are built around a trill: a fast alternation between two adjacent notes (separated by a half or whole step e.g. CDCDCD or ED#ED#ED# etc) and are played with two adjacent fingers (usually your pointer and middle finger). In music these trills when part of an ornament are often needed to be played very fast (at least 10 notes per second).
My technique is very advanced except for these ornaments when played with my right hand. I can play an 8 notes per second trill easily with my right hand but anything faster is difficult and impossible sometimes. I double checked with all the books on harpsichord playing I have and I'm doing the correct hand and body posture. I'm keeping the movement of my fingers as simple as possible which is what every book teaches. I've consulted with many other harpsichordists and from what I can tell I'm doing exactly what they say to do yet all the very long and fast ornaments I can't seem to get my fingers to move up and down fast enough.
All the materials on harpsichord performance say to have as little body movement as possible. The hand should be light with the fingers forming a slight arch (rather than being straight like some amateurs do). Your hand and arms shouldn't be tight at all and the only thing moving should be your fingers from your knuckles. I'm doing all this from best I can tell.
Oddly, my left hand has no problem whatsoever with ornaments yet I'm right handed. My left hand can do everything I want my right hand to do. It feels like a completely different process goes into playing ornaments in my left hand yet I can't seem to duplicate it at all with my right hand. My left adopts almost the same posture as my right hand when playing ornaments except that my ring finger of my left automatically straightens slightly outward when playing a trill with my pointer and middle. My right hand's ring finger automatically bends inward towards my palm.
I have no pain whatsoever in either of my hands or arms so I take that as a good sign at least.
I have been practicing ornaments for at least an hour a day for the past month and a half. I have made some progress but it's been slow and I'm getting desperate so I'm looking for perhaps some suggestions for exercises if any that I could do away from the keyboard that might increase my finger speed. I've found exercises online meant to improve "grip strength" and "flexibility" but I'm not sure if those are the right exercises that might increase speed.
For the past few weeks I started doing some finger exercises such as bending the fingers of one hand back with the other and that seems to help somewhat.
