Sounds that are made when vocal cords stay close together are called voiced sounds, such as \[b\], \[g\] in English.

Sounds that are made when vocal cords stay apart are called unvoiced sounds, such as \[p\], \[k\] in English

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San Jose State University

There are several ways of classifying sounds or phones in language:

1)	Voiced or unvoiced

2)	nasal sound or non-nasal sound

3)	Consonant, vowels, or semivowels


Different Classifications of Sound/Phones

An on-going but a helpful book resource about NLP
https://web.stanford.edu/~jurafsky/slp3/

Speech and Language Processing (3rd ed. draft) 

Voiced And Unvoiced Sound

Nasal sounds are the sounds that are made when the air passes through the nasal tract as opposed to the oral tract. (Nasal and oral tract together are two components of the vocal tract.) At the same time, nasal sounds use both nasal tract and vocal tract as resonant cavities.

Nasal Sound and non-Nasal Sound

Consonants are the sounds you make when you block the flow of air in some way. Examples include \[z\], \[b\], \[f\], and others. Consonants can be voiced or unvoiced.

Consonant

Vowels are the sounds you make when there’s less obstruction of airflow coming out from your lung. Vowels are mainly voices. Examples include \[ae\], \[au\], \[ow\] and others.

Vowels

Semivowels are sounds that are less obstructed just like vowels, and meanwhile are short and not syllabic just like consonants. Examples include \[y\], \[w\] and others.

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