PHYS 103 lecture 29

voice acoustics

Vocal anatomy

Air flow through vocal folds produces “buzzing” (like lips)

Frequency is determined by• thickness (mass) men have lower pitch• muscle control (stiffness)

Vocal tract acts as a resonator• length is fixed (15-20 cm)

Vocal Spectrum

Sound entering the trachea is close to a pulse train ( many harmonics of nearly equal amplitude)

Similar to organ reed: frequency of vocal folds is not much susceptible to feedback (vocal tract resonances) – it is determined mainly by muscular control

Vocal spectrum

pulse train

vocal folds “buzz”

vocal tract resonances

final sound

source

filter

+

How we get vowels

Recall: 1. timbre of sound depends on the relative amplitude of harmonics2. pitch depends on the frequency of the fundamental

Resonance frequencies of vocal tract shape the spectrum -> determine timbre

Different vowels (same pitch) are essentially different timbres

We control the frequencies of formants by changing the shape of the vocal tract

Resonance frequencies of the vocal tract are called formants

First formant typically controlled by mouth opening

Second formant typically controlled by tongue position

Example spectra

aaa

iii

ooo

first formant

(wide open mouth)

(mouth more closed)

More examples – effect of tongue placement

uuuu

wrwr

second formant

The spectrogram:a tool for measuring the voice

spectrum

time

frequency

freq

uenc

y

ampl

itude

spectrogram