It is a good skill to be able to bow different lengths, but still make each bow stroke sound the same. To practice this, divide the bow into eighths with tape (ideally on a spare bow if you have one). Play one even stroke per segment across the bow, and focus on getting an equal sound. Then try alternating playing across two segments, then one (a quarter followed by an eighth), still producing the same quality of sound for each stroke.
Within the repertoire, it is rare that notes within a phrase are played with the same length of bow. With the bow divided into these segments, it is helpful to organize each phrase by how much length each note requires. At first everything should be even, then gradually build to more complex groupings. Every motion of the bow needs to be carefully planned out.
The best way to get a legato is actually to practice everything in repeated staccato notes. This helps the legato line sound much more steady and even as it builds complete awareness of exactly how much bow is needed for each note of the phrase.
This approach also helps with feeling the balance of the bow. As the bow draws across the string, the weight shifts from frog to tip. At each increment, the hand can adjust as necessary to the changing balance. When playing at the frog, the little finger can add pressure to compensate for the weight, and then gradually release moving towards the central position. If the little finger is not engaged, the thumb is probably squeezing too hard.
There are many combinations of bow speeds we want to be able to achieve:
Being able to control all combinations of bow speed and volume is essential to building phrasing.
Bow control using the little finger engages the abductor digiti minimi muscle. This is countered with the first finger and thumb. The base knuckles should remain reasonably straight through all motions of the bow hand.
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