One ejecting vocal person now saying "t-w-i-t-t-e-r" seven times faster? (8)

'one ejecting vocal' is the definition.
The definition suggests a singular noun which matches the answer.

'person now saying t-w-i-t-t-e-r seven times faster?' is the wordplay.
I cannot quite see how this works, but
'person' could be 'ex' (ex is a kind of person) and 'ex' is found in the answer.
'e' is found in the answer.
'r' is within the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?