LING 1001 B
January 23, 2014
• Looking at the physical aspects of the sound wave (acoustic characteristics of the
• What is a sound wave?
• Disturbance in the air set off by a movement
• Violin strings
• Vocal folds
• Not permanent
• Air molecules that want to keep a comfortable distance from each other.
– One moves to right, the other move to the right as well.
Compression = Molecules are more crowded together than usual
Rarefaction = Molecules are spread farther apart than usual
Periodic wave = Sound wave that repeats at regular intervals
Hertz =Unit of measurement
- 20 – 20 000 Hz = perceived as sound
- Highest frequency of telephone: 3 500 Hz
• Very little essential information is lost
Complex sound waves
• Simple sound waves at single frequencies that combine – See Figure 3, p. 71
• Sound wave produced by vocal folds = complex wave
Vocal fold complex sound wave
• Fundamental wave
– Repeats itself at the frequency of the opening and closing of the vocal folds
• Set of harmonics
– Repeat at frequencies which are multiples of the fundamental.
• Vocal fold complex sound wave
– Fundamental wave at 120 Hz
– Second harmonic at 240 Hz, third at 360 Hz, …
– First harmonic = fundamental frequency (pitch)
• Source wave
– Source: vibration of vocal folds in response to airflow from the lungs
– Filter: vocal tract (acoustic resonator)
• Acts as a filter to selectively transmit frequencies (produced by the larynx
or within the vocal tract itself) through it.
• Filter (vocal tract)
Think of it as
1. a tube, closed on one end (glottis), open at the other end (lips)
This type is called quarter-wave resonator.
2. a series of air-filled containers hooked up to each other.
– Each container transmits certain frequencies.
– Each has its own resonating frequencies (RF).
– Overall RF differs from each of the single containers.
3. A variable resonator (frequency response changes depending on its shape) • Average male’s vocal tract: 17 cm in neutral position.
• Quarter-wave resonator. Therefore, wavelength of the lowest RF is 17 x 4 = 68 cm
• Formula to convert wavelength to frequency is
Frequency = speed of sound divided by wavelength
– Speed of sound: 34 000 cm/s
– 34 000/68 = 500 Hz
• Higher RFs of the vocal tract are odd-number multiples of the lowest.
– Next resonance is at 1500 Hz, then 2500 Hz, then 3500 Hz…
– These RFs are called formants.
• Sound emerging from the filtering system has the same fundamental frequency and
harmonics of the glottal sound.
• Amplitudes of the harmonics have changed.
– Some harmonics have been amplified, others have been damped.