Place your fingertips on the front of your neck, and pronounce the following words. What do you feel on your fingers when you say the underlined sound?
vow | fake (vvv | fff)
zebra | snake (zzz | sss)
–> When we pronounce voiced sounds, our vocal chords vibrate when we say those sounds. [v] [z]. Did you feel the vibration?
–> When we pronounce voiceless sounds, our vocal chords do not vibrate. [f] [s]. No vibration.
This vibration or lack of vibration then carries forward to the following sound in the word. Therefore, this vibration or lack of vibration explains why we pronounce the past tense of verbs in three voiced or voiceless ways: [t], [d] or [Id].