While practicing vibrato (I've just started) I noticed that while vibrating, for example, on the D string with my third finger using the wrist, when I pull back and forth the third finger, while pulling back, it sleeps on the A string. I tried to vibrate where my third finger moves in such a way that it doesn't lean on to the other string when it's downwards but it doesn't seem to help. So I wanted to ask that is it normal for the vibrating finger to do that?
is it normal for the vibrating finger to do that?
It is never normal to do that regardless of whether you are vibrating or not. You will have to learn to stop doing this when you come to play double stops on none-open strings because if one of your fingers touches the adjacent double-stopped string you get a horrible sound.
When you vibrate you do not move your finger from side-to-side. You try and move it as much as possible in the line of the string.
The only time one finger should touch two strings at the same time is when you are playing a fifth where the same finger is deliberately holding down two strings at the same time.