It is a stylistic effect that is used in voice, essentially a small pitch bend of any given note and it’s a fast oscillation or vibration of the note.
straight tone
with vibrato
2. Do I need vibrato?
If you are a classical singer, we need it all the time.
rock, pop, contemporary, R and B, country
3. Can we change the speed of it?
6Hertz when we hear vibrato
change the amount of hertz, flip per second
Too slow:
maybe depressed larynx
maybe too much air
maybe imitating someone had a really slow vibrato