A shaky bit of singing (5)
I believe the answer is:
trill
'a shaky bit' is the definition.
'trill' can be an answer for 'bit' (I have seen 'bit of birdsong' mean 'trill' so perhaps 'bit' could also mean 'trill'). I'm unsure of the 'a shaky' bit.
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for trill that I've seen before include "Warbling sound made by a songbird" , "Quavering or vibratory sound" , "Sound of rapidly alternating notes" , "High-pitched warbling sound" , "sing" .)