P105 Lecture #27 visuals

20 March 2013

Sound production from vocal system

• Three components:– Power source (lungs)– Oscillator (vocal folds spring-mass system, driven by Bernoulli effect)– Resonator / Radiator (vocal tract and mouth subject of today’s lecture)

• Recall, periodic emission of puffs of air though glottal opening (due to vibration of vocal folds), constitutes a pressure wave with a discrete (harmonic) frequency spectrum: – fundamental is at the vocal fold vibration frequency & determines the pitch; – harmonics are down by 12 dB after each octave (factor of 2 increase in frequency).

i.e., LI (n=2) = LI (n=1) – 12 dB; LI (n=4) = LI (n=2) – 12 dB, etc.

• To understand harmonic structure of speech & singing must also take into account the filtering effect of the vocal tract and mouth. – This is the subject of today’s lecture.

Net Result: Periodic expulsion of “puffs” of air from lungs

From Rossing, Wheeler & Moore, The Science of Sound

Top: volume velocity vs time for sound production at 125 Hz (male voice); Bottom:Power spectrum falls at 12 dB per octave

Fourier Spectrum:

Impact of the vocal tract geometry:Formants

Can think of the vocal tract as an air-filled pipe, closed at one end (folds) & open at the other (mouth)

Standing wave modes = “formants”Nominally odd harmonics only:

fn = n (v / 4L), v = 343 m/sL ~ 17.5cm f1 ~ 500 Hz.

In practice, geometry is complex, formant frequencies influenced by tongue, jaw mouth, etc…

Illustration from J. Sundberg, “The Acoustics of the Singing Voice”

How can you vary your formants?

from J. Sundberg, “The Acoustics of the Singing Voice”

Shape of oral cavity, mouth opening, & location of tongue are very important

For example, a constriction at a location of a formant’s pressure node will limit impact of that formant

Also, can amplify higher freq. modes with antinode at that location

Making different vowel sounds

from J. Sundberg, “The Acoustics of the Singing Voice”

from J. Sundberg, “The Acoustics of the Singing Voice”

Making different vowel sounds