Overview
This lecture covers the physiological structure and acoustic properties of the human vocal tract, focusing on how the voice produces pitch, timbre, and formants.
Human Voice Capabilities
- The human voice has fine pitch control, a wide dynamic range, and can produce many timbres.
- Voices can remain audible over loud orchestras and maintain clear articulation of text.
Basic Physiology of Voice Production
- Voice production involves the lungs, vocal folds (glottis/larynx), and vocal tract (mouth, nose).
- Lungs act as an air reservoir, similar to some wind instruments.
- Air travels up through the trachea, larynx, and into the pharynx.
- The glottis (vocal folds) controls airflow; tensing for speech or singing, relaxed for breathing.
- Forced air causes vocal folds to vibrate, creating sound waves.
- The vocal tract (pharynx, mouth, nasal cavity) shapes the sound’s timbre and resonance.
Pitch and Timbre Control
- Pitch is determined by the repetition frequency of vocal fold vibrations, influenced by mass and tension.
- Male vocal folds are generally larger and more massive, leading to different pitch ranges.
- Higher pitch is achieved by increasing tension, making folds thinner and shorter.
- The loudness and quality of sound depend on how the vocal folds close during each cycle.
- The harmonic spectrum from the folds decreases by 12dB per octave (faster with breathier voices).
- Spectral control is influenced by breathiness and airflow through the folds.
Resonance and Formants
- The vocal tract acts like a tube, amplifying certain harmonics known as formants.
- Formants are critical in shaping vowel sounds, which can still be recognized without pitch (e.g., whispered formants).
- Typical male vocal tract length is about 175 mm; female about 150 mm.
- Vowel formants (F1, F2, F3) distinguish different vowel sounds.
Anatomy of the Vocal Tract
- Key parts: lips (labia), teeth, alveolar ridge, hard palate, soft palate (velum), uvula, pharynx, larynx, and various tongue regions.
- The velum’s position determines whether air escapes through the mouth or nose.
Vowel Formant Table
- “ee” (beet): F1=250 Hz, F2=2290 Hz, F3=3010 Hz
- “ah” (father): F1=730 Hz, F2=1090 Hz, F3=2440 Hz
- Other vowels have distinct formant frequencies (see table above).
Key Terms & Definitions
- Glottis — The opening between the vocal folds where sound is generated.
- Formant — Resonant frequency of the vocal tract that shapes vowel quality.
- Pharynx — The throat cavity behind the mouth and nasal passages.
- Velum — The soft palate that controls airflow to the nose.
- Harmonic Spectrum — Distribution of sound energy among integer multiples of the fundamental frequency.
- Breathiness — Quality determined by the amount of air passing through the vocal folds.
Action Items / Next Steps
- Review voice anatomy and the function of each vocal tract part.
- Study the vowel formant table for recognition and distinction between vowels.
- Complete any assigned readings and practice analyzing vocal spectra in sound software (e.g., MatLab).