PHYS 1240 Sound and Music Professor John Price Cell Phones off Laptops closed Clickers on Transporter energized
The Ear and Hearing Thanks to Jed Whittaker for many of these slides
Ear anatomy substructures Ossicles Semicircular Canals Ear Drum Cochlea
Ear anatomy Outer Ear (Resonator) http://www.nidcd.nih.gov/staticreso urces/health/hearing/images/normal_ ear.asp
Ear anatomy Middle Ear (Impedance Matching) Outer Ear (Resonator) http://www.nidcd.nih.gov/staticreso urces/health/hearing/images/normal_ ear.asp
Ear anatomy Middle Ear (Impedance Matching) Outer Ear (Resonator) Inner Ear (Fourier Analyzer) http://www.nidcd.nih.gov/staticreso urces/health/hearing/images/normal_ ear.asp
Ear Animation Waves on the basilar membrane: from Human Anatomy (McGraw Hill) Hearing protection reflex
The outer ear The human ear is most responsive at about 3 khz
18-1 Let s model the outer ear as a straight tube closed at one end. About how long is? A) 0.4 mm B) 4 mm C) 28 mm D) 56 mm E) 162 mm
18-2 Tube closed at one end What quantity is plotted above? A) pressure B) displacement
18-3 What is the resonant frequency of the first mode of the ear canal? A) 100 Hz B) 500 Hz C) 1200 Hz D) 2100 Hz E) 3100 Hz
Outer ear resonator The length of the human auditory canal is This gives a fundamental mode of ff 1 = 3.1 khz
Ear sensitivity Outer ear is a low-q cavity; other frequencies pass through also W. J. Mullin, W. J. George, J. P. Mestre, and S. L. Velleman, Fundamentals of sound with applications to speech and hearing (Allyn and Bacon, Boston, 2003)
18-4 Why have a middle ear? A) To provide peak sensitivity at 3 khz B) To better couple pressure waves from air medium to liquid medium C) To protect the inner ear from extremely loud sounds D) For balance E) More than one of the above
The human ear is closely related to other animal ears
Bones make fossils! 200 Mya 300 Mya
How does the inner ear work? 35 mm
Waves on the Basilar Membrane
How does the inner ear work?
How does the inner ear work? 30 µm Auditory Transduction animation by Brandon Pletsch Transmission electron microscope image, hair cells from a rat cochlea by R. Pujol
18-5 How big is 30 µm? A) Diameter of a human hair B) Size of a red blood cell C) Size of an atom D) Size of the nucleus of an atom E) Size of an amino acid molecule
18-6 How big is 0.1 nm? A) Diameter of a human hair B) Size of a red blood cell C) Size of an atom D) Size of the nucleus of an atom E) Size of an amino acid molecule
18-7 How does the wave velocity on the basilar membrane compare to the sound velocity in air? A) About the same B) Much slower C) Much faster
Hearing Damage Basilar Membrane Auditory Nerve Fiber
Hearing Damage OHC = Outer Hair Cell IHC = Inner Hair Cell
Hearing Damage
Hearing Damage Developed by Elliott Berger, MS, Senior Scientist with 3M Occupational Health and Environmental Safety Division (see link to 3M ear plugs )
PHYS 1240 Sound and Music Professor John Price Cell Phones off Laptops closed Clickers on Transporter energized
Psychoacoustics Measures of loudness Loudness versus frequency (Fletcher-Munson) Just noticeable difference (JND) of intensity and pitch Masking effects Pitch perception Phantom fundamentals Perception of direction and time differences Listener comfort and discomfort Conditions for intelligibility Music compression (MP3 and similar schemes)
Range of Hearing Sound Intensity Level (db)
Sound Intensity Recall Sound carries energy, rather than drops of water. So sound intensity is Intensity = joules seconds meters 2 = energy time area watts meters 2 = WW m 2 O when the Saints! Go marching in!
Recall The threshold of hearing is about 10 12 WW/mm 2 at 1 khz, where the ear is most sensitive. (The corresponding pressure amplitude is 2 10 5 Pa.) But away from 1 khz, the same intensity may seem much less loud. Intensity does not equal loudness!
The bel is used to express an intensity ratio R. Recall RR = 10 bels 1 bel = 10 decibels (db) The function that inverts this expression is called log() bels = log(rr) Sound Intensity Level = SIL Reference Intensity: II 0 = 10 12 W/m 2 RR = II II 0
19-1 The decibel (db) is one tenth of a bel. Suppose R=10000. How many decibels is this? A) 0.5 B) 40 C) 50 D) 0.4 E) 400
19-2 Suppose sound A has an intensity of 7 W/m 2, and sound B has an intensity of 0.07 W/m 2. What is the ratio of A to B expressed in db? A) 100 B) 20 C) -10 D) -20 E) none of these
19-3 Suppose sound A has an intensity of 7 W/m 2, and sound B has an intensity of 0.07 W/m 2. What is the ratio of B to A expressed in db? A) 100 B) 20 C) -10 D) -20 E) none of these
19-4 Suppose you are 10 m away from an acoustic guitar and you measure an average sound intensity of 10-9 W/m 2. What SIL does this correspond to? A) 30 db SIL B) 20 db SIL C) -90 db SIL D) 90 db SIL E) none of these
19-5 If a sound is 0 db SIL, is the intensity equal to zero? a) Yes b) No
19-6 If a sound is 0 db SIL, can you hear it? a) Yes b) No c) Depends on the frequency
Fletcher-Munson curves a topic in psychoacoustics 100 SIL (db) constant perceived loudness?? 0 10 100 1000 10000 Frequency (Hz)
Fletcher-Munson curves a topic in psychoacoustics 100 SIL (db) 0 constant perceived loudness 0 phons 10 100 1000 10000 Frequency (Hz) Threshold of hearing contour
19-7 Around what frequencies are you most sensitive to low intensity sound? A) Low freq s (~20-200 Hz) B) Middle freq s (2-4 khz) C) High freq s (10-20 khz)
Fletcher-Munson graph 100 constant perceived loudness SIL (db) 50 0 10 50 phon 0 phon 100 1000 10000 Frequency (Hz)
Phons loudness scale For a tone at 1 khz, the loudness in phons is equal to the sound intensity level (SIL) in db. At other frequencies, the SIL is adjusted so that tones with equal perceived loudness have equal loudness in phons. The Fletcher-Munson curves show the SIL in db for tones with any loudness in phons and any frequency.
19-8 You re listening to a 50 db SIL sound at 1 khz. If you want to listen to much lower pitches, feeling the same loudness to you, should the SIL (in db) of the lower frequency sound be A) HIGHER than 50 db B) LOWER than 50 db C) Still 50 db
Fletcher-Munson graph 100 100 SIL (db) 0 50 0 phon 10 100 1000 10000 Frequency (Hz)
Fletcher-Munson graph
19-9 Which will seem like a bigger increase in loudness? A) Increasing by 60 db intensity, while listening to 125 Hz sound B) Increasing by 60 db intensity, while listening to 1000 Hz sound C) Both seem equally more loud
Fletcher-Munson graph 60 db intensity increase
19-10 Music is recorded faithfully at a loud concert. You play it back at home on a high-quality sound system, and turn down the volume (reducing the intensity of all frequencies by the same # of db) How will it sound? A) Same, just quieter B) Low frequencies will be over-emphasized ( bass-y ) C) Low frequencies will be under-emphasized ( treble-y )
19-11 Music is recorded at a soft concert. You play it at home, and crank the volume (increasing ALL intensities by the same # of db) How will it sound? A) Same, just louder B) Low frequencies will be over-emphasized C) Low frequencies will be under-emphasized
Another loudness scale: phons versus sones Two sounds with the same phons loudness have the same perceived loudness. But a sound that is twice as loud is not twice as many phons. Sones correspond better to what we mean by loudness, in that twice as loud does correspond to twice as many sones. Φ phons 40 Ψ sones = 2 10 (This is a simpler way to define sones compared to our text.)
19-12 Another loudness scale: phons versus sones Φ phons 40 Ψ sones = 2 10 40 phons is equal to how many sones? A) 3 B) 2 C) 1/2 D) -1 E) 1
19-13 Another loudness scale: phons versus sones Φ phons 40 Ψ sones = 2 10 50 phons is equal to how many sones? A) 3 B) 2 C) 1/2 D) -1 E) 1
19-14 Another loudness scale: phons versus sones Φ phons 40 Ψ sones = 2 10 30 phons is equal to how many sones? A) 3 B) 2 C) 1/2 D) -1 E) 1
Another loudness scale: phons versus sones Φ phons 40 Ψ sones = 2 10 Doubling the sones loudness is equivalent to going up 10 phons. Half the sones loudness is equivalent to going down 10 phons.
Masking and Critical Bands A quiet sound can be masked by a louder sound if it is close enough in frequency. The critical band is the frequency range or band width that is masked. YouTube: Francesca Dunne on critical bands MP3, AAC and similar lossy audio compression algorithms rely on masking to throw away less-important information 10x reduction in file size
19-15 Suppose I play a loud sine wave with a frequency of 2 khz. If I also play, at the same time, a quieter sine wave with a frequency of 3 khz, will it be masked by the louder sound? A) Yes B) No Figure from Hartmann Ch. 12 (solid line is critical band width)
More psychoacoustics JND = just noticeable difference JND for sound intensity depends on frequency and sound level JND for frequency depends on frequency and intensity
JND for sound intensity (from text by Hall) Implications for gain controls, Grace Audio site
19-16 A typical JND for sound level is about 1 db. Roughly what percent change is that in the intensity? 10 10 =10000000000 10 1.0 =10 10 0.1 =1.2589 10 0.01 =1.02329 A) 1% B) 1.3% C) 13% D) 25% E) 100%
JND for frequency
19-17 Suppose you listen to a 4000 Hz sinusoidal tone at 40 db SIL. Then you listen to a similar tone at 4020 Hz. Can you reliably tell that the second tone is higher frequency? A) Yes B) No