(4) Nasals:

 

Nasal sounds such as English m , n are periodic. They are similar to vowels, but they have much less energy at higher frequencies and it is very difficult to identify formants in their spectrum. This is mainly because most of the sound generated in the larynx by the vibration of the vocal folds cannot escape out through the mouth as it does in the case of vowels, but has to pass through the nasal cavity and out through the nostrils.