[starsailor]

Hi Noodler your head voice really covers the higher range, so you probably need to practice going deeper using your chest and get more control over your head voice, not too sure about the quivering that could be a lack of power or hesitance if a person is doing it unintentionally, check this link out, there is loads of information here and check out Passagio which is used in regard to note transitions, you're vocal coach may have mentioned this already


Voice Registers: Chest, head and other voices at Vocalist.org.uk