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Physics 1251 The Science and Technology of Musical Sound Session 43 MWF Summary and Review Physics 1251 Session 43 MWF Summary and Review What is MP-3 and how does it do its “magic?”
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Session 43 MWF
Summary and Review
What is MP-3 and how does it do its “magic?”
MIDI is a control protocol that can make the sound card in our PC play music.
MIDI coded Christmas Carols
Computer based music exploits novel “tonal possibilities.”
Lamentation for Jerusalem
For solo Saxophone and DMIX
By Daniel V. Oppenheim
What one hears can be objectively characterized by a time-dependent “Vibration Recipe” or the “Frequency Spectrum” (Fourier Spectrum):
The acoustic properties of the room affect the time dependence of the vibration recipe.
The reverberation time is an important property of a room.
Intensity of Sound in a Room:
I = Io‧ 10 –6 t / TR
t = ⅙ TR
~ 1/10 Io
t = ⅓ TR
~ 1/100 Io
80/20The Sabine Equation:
I = Io‧ 10 – 6 (t/TR)
TR = 0.16 V/Se
Se = α1 S1 + α2 S2 + α3 S3 + α4 S4 +…
The psychoacoustic response of the human ear is frequency dependent.
Fletcher- Munson Diagram
Fletcher and Munson (1933) J. Acoust. Soc. Am. 5, 82-108
of Hair Cells (HC)
varies with distance
from the stapes.
The character of sound depends on physical acoustical phenomena as well.
Intensity is Power per Unit Area
Why 1/r 2?
Area = 2/3π ‧ r 2
I = Power/Area
I2 = I1 (A1/A2)
I2 = I1 (r1 / r2) 2
A = ⅔π r 2
When the surface is smooth we have “specular” (mirror-like) reflection.
Roughness ≲ λ
Refraction occurs when a wave “enters” a medium that has a different velocity?
V1 < V2
What happens when a wave “is partially obstructed?
Doppler Shift: Moving source
fobserver = fsource [v + vobserver] / [v – vsource]
Out of phase
The Normal Modes of Oscillation determine the frequencies present in the radiated sound.
A Standing Wave results from interference of counter-reflecting waves.
f1 = vstring / λ1 = vstring / 2L
80/20The distance between neighboring nodes & antinodes is ¼ λ. [ “N-A d = ¼ λ” ]
f2 = vstring / λ2 = vstring / L
Open Cylinder Np – Np
fn = nf1
f1 = v/2L
Stopped Cylinder Ap – Np f2n-1 = (2n-1)f1 f1= v/4L
Stopped Cone Ap – Np fn = nf1 f1= v/2(L+c)
Stopped Combination Ap – Np fn = nf0f0= (1+ξ)v/4(L+c)
Comparison of Wind Instruments (cont’d.)
f1 = v/2L
f1 = v/4L
f1 = v/2(L+c)
Anatomy of the Human Voice
80/20The vocal folds comprise muscle, lamina propria and epithelium.
Lamina Propria (3 layers)
Harmonics align with Formants
Formants and Singing
The Modes of Oscillation of a Clamped Membrane
Mode: (0,1) xn m / x0 1 : 1
80/20The timbre of an instrument’s sounds depends on its vibration recipe.
fn = n f1
fn m = xn m f1
fn m = xn m f10
f01Physics 1251 Unit 3 Session 34 Percussion with Pitch
80/20The task of producing pitch in a percussion instrument is an exercise in manipulating the overtones into a harmonic series.
Bending Modes in Bars:
f1= 1.133 fo
f2= 3.125 fo
What is musical sound?
Harmonics are the key.
Harmonics! The harmonics must be “in tune” to avoid beats.
Why does this work?
What is special about the harmonics used in standard music?
Microtonalists say “nothing!”
8:00 – 10:00 am Room 102