amplitude
amplitude
Which of the following frequency spectrum graphs
represents this sound wave?
A
C
f1
f1
6f1
amplitude
amplitude
f1
B
6f1
6f1
D
f
6f
Phys 1240: Sound and Music
www.colorado.edu/physics/phys1240
LAST TIME: Spectra.
TODAY: Spectra, human voice.
NEXT TIME: Final review.
READ: Practice final – pick questions for review.
• In-class diagnostic test Thursday – worth 30 clicker
questions.
• Homework 12 and Reading Question 14 due Friday
night.
• Extra help-room hours and review sessions this
week.
• Pre-final office hours Monday 5/7.
Review sessions & help-room hours
• Help-room hours
– Tuesday: 1:45-3 pm (no 3-5 pm!)
– Wednesday: 2-4pm
– Thursday: 11am-noon , 1:45-4 pm (no 4-5 pm!)
– Friday: 2-4 pm
• Review Sessions (in help room):
– Thursday 4-6 pm
– Friday 4-6 pm
• Pre-final office hours – Monday 5/7
– Ed Kinney 10am-1 pm, Duane F227
– Meredith Betterton 1-3:30 pm, Duane F629
Clicker question
Consider the following waveforms:
Which of the following are true:
i) Both have the same fundamental frequency
ii) Both have the same frequency spectrum graphs.
A) i and ii are true
B) i and ii are false
C) i is true, ii is false
D) i is false, ii is true
Clicker question
Consider the sawtooth waveform, which has a steep
(rapidly changing) section:
What does this imply about the waveform’s frequency
spectrum graph?
A) The spectrum must include only low harmonics (low
frequencies).
B) The spectrum must include some very high
harmonics (high frequencies).
C) Nothing, the steep section is unrelated to the
frequency spectrum graph.
Spectral analysis
PhET spectrum analyzer
1.
2.
3.
4.
Single frequencies
Multiple frequencies
Wave game
Complex waves
Real spectra
Ideal instruments produce only sounds at exact
(harmonic) frequencies
Real sounds contain all frequencies
(but with peaks at the harmonics!)
Pure tone
Waveform
Frequency spectrum
Piano note
Waveform
Frequency spectrum
Spectrum analysis software
Visual Analyzer
• Analyze some instruments
Frequency ranges for typical music, from 20s to 00s.
Green Edith Piaf 1937
Red = Led Zeppelin 1971
Blue = ColdPlay 2001
Vocalizing vowels
Periodic (pitch!)
Spectrum is harmonic
Like a "reed" instrument
(vocal cords)
Can sustain "ah"
Can't sustain "oi" like "oil"
Formants
Formants:
Certain ranges of frequency are enhanced
(or suppressed), to form a particular vowel
An “envelope”
The shape of the envelope determines what
vowel you hear!
consider a cylinder
What are the
resonant frequencies?
Ideal spectrum of cylinder
of some given size
1 kHz
2 kHz
3 kHz
Possible spectrum of (real) cylinder
of some given size
1 kHz
2 kHz
3 kHz
250 Hz source (with lots of harmonics)
1 kHz
2 kHz
3 kHz
send that 250 Hz sound (with lots of
harmonics) through the cylinder:
"Formant"
1 kHz
2 kHz
3 kHz
Clicker question
If you pass a 250 Hz sound with lots
of harmonics through a cylinder
with a resonance peak at 1000
Hz, what frequency will you
hear?
"Formant"
A) Mainly 250 Hz
B) Mainly 1000 Hz
C) Something else
1 kHz
2 kHz
3 kHz
send that 500 Hz sound (with lots of
harmonics) through the cone:
SAME Formant
1 kHz
2 kHz
3 kHz
Voice
Exploratorium "duck calls"
www.exploratorium.edu/exhibits/vocal_vowels/vocal_vowels.html
Vocal cords
• The analogue of
the duck call for
the human voice
is your vocal
cords
• Located in the
larynx (voicebox)
Top view of larynx
• Air moving through
trachea causes vocal
folds (cords) to open
and close
• Video of vocal cord
motion (Laryngeal
videostroboscopy):
https://www.youtube.
com/watch?v=v9Wdf
-RwLcs
Vocal cord oscillations
• Bernoulli effect:
higher fluid
velocity -> lower
pressure
• Difference in
pressures needed
to speed up fluid!
• Demos:
– Sheet of paper
– Ping pong balls
Clicker question
If you pass fast moving air over the top of a sheet
of paper, how do you expect the pressures to
compare on the top and bottom of the sheet?
A) Same pressure on top and bottom
B) Higher pressure on top, lower pressure on
bottom
C) Lower pressure on top, higher pressure on
bottom
Bernoulli effect in the vocal
cords
• Air flow produces low
pressure, pulls vocal
cords toward each
other
• Muscles act as
springs, pull vocal
cords apart
• Oscillation!
– Women: 140-400 Hz
– Men: 70-200 Hz