Voicing is a phenomenon that happens in human pronunciation, when vocal folds vibrate during the pronunciation of certain sounds. This happens in English but also in Spanish.
To check when voicing happens, put the palm of your hand around your neck and feel the slight vibration of your vocal folds.
In English, the distinction between voiced and voiceless consonants is very important as it helps tell apart different sounds that otherwise would sound the same.
These are produced with vocal fold vibration. If you place your hand on your throat, you should notice a light vibration. These are blurry sounds.
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Vowel sounds are always voiced.
These are produced with no vibration, with a complete opening of the vocal folds. These are clear, pure sounds.