What characterizes an unvoiced sound in phonetics?

An unvoiced sound in phonetics is characterized by the absence of vibration of the vocal cords during articulation. When producing unvoiced sounds, the airflow is not accompanied by the vocal folds coming together and vibrating, which is a defining feature of voiced sounds.

For example, in the case of unvoiced consonants like /p/, /t/, and /k/, the speaker can produce these sounds without any vocal cord vibration, resulting in a clearer, more distinct sound that can be easily identified as unvoiced.

The other options present characteristics not associated specifically with unvoiced sounds. While voiced sounds do involve vocal cord vibration, the nature of an unvoiced sound rests entirely on the lack of this vibration. The idea of the sound being always nasal can apply to some voiced sounds, but it does not pertain to the classification of unvoiced sounds. Additionally, there is no restriction on the occurrence of unvoiced sounds being limited to the beginning of words; they can appear in all positions within words, further highlighting the significance of understanding their defining characteristic of having no vocal cord movement.