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 harmonics 2.pitch depends on the frequency of the fundamental Recall: 1.timbre of sound depends on the relative amplitude of harmonics 2.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 amplitude spectrogram