Female 2 Formant frequency 2 Humans 2 Male 2 Phonetics Speech Acoustics 2 Voice 2 adult 2 article 2 female 2 human 2 male 2 phonetics 2 physiology 2 speech 2 voice 2 vowel 2 Acoustic structures 1 Acoustic variables 1 Acoustics 1 Adolescent 1 Adult 1 Aging 1 Biological Variation, Individual 1 Biological Variation, Population 1 Child 1 Child, Preschool 1 Fundamental frequencies 1 Glottis 1 Intra speaker variabilities 1