hi, i am a college music major on viola, and i have played viola for 10 years. i have always been sort of a closet violinist (not that good compared to violin majors, but still loving it hehe), but lately i have been playing violin a lot and i think i want to double major in it.
how many of you have experience playing both violin and viola? how do you navigate the issues of switching between the two? besides the clef and key differences (not so bad once you get used to it), i always have trouble with making a good tone on the violin. i am used to the bigger size of the viola and i end up overdoing it also, my vibrato on violin is so sluggish! (and how do you vibrato up high really fast?) i would love to get that really gorgeous intense sound that comes from a faster vibrato. i would really appreciate tips from anybody who has found any success with these issues (: thanks!

I can appreciate the problem. Try going back to the old vibrato exercise of moving the wrist to a specific rhythm - eighth notes, triplets, sixteenths. And after developing a steady pattern in each of those, then go faster. Make sure it is the wrist moving and not the forearm. Dr. Allard teaches that to get that rich vibrato in performance, some notes need to be "attacked" (my approach) with an intense, fast vibrato and then let the note settle in with a steady vibrato as it is held. That attack is with your vibrato, not meant to imply bowing. Good luck. Practice.

to your question about high fast vibrato i would go with what earl said but, for higher notes it is a good idea to let the vibrato find its own tempo when you practice and slowly push your self to go a little faster every time until you get it to the speed you want.
truth be told vibrato can't really be tought it just has to come teaching just helps it get there.