Vibration and no vibration
(Voiced and unvoiced)

When we speak we make some sounds with vibration in our voice box and some without vibration.
All vowels and many of the consonants are said with vibration in English.

Often the vibration is very small so you may not notice it.

To feel the difference, put your hand firmly on your voice box at the front of your throat and say:

ssssssssssssssss  Do you feel the vibration?

zzzzzzzzzzzzzzzzzz  Do you feel the vibration?

Here is a table of the consonants without vibration in English
and the corresponding consonants with vibration.

no vibration p t k f th s sh tch
with vibration b d g v the z je dj

th as in thank
the as in the
sh as in she
je as in pleasure
tch as in catch
dj as in edge

This will help you to understand the different pronunciations of the -ed verb endings