l 20 course review w= mg, where g=9.8 m/s 2 in previous slide w (=f g ) = f n
TRANSCRIPT
L 20Course Review
W= mg, where g=9.8 m/s2
In Previous slide W (=FG) = FN
Simple Harmonic Motion• Position x vs. time t• Definition of period T• Definition of amplitude A
Frequency and Periodf = 1/T or T = 1/f or f T =1
T period, in seconds (s)f = frequency in Hertz (Hz)
Metric prefixes:centi- (c), milli- (m), micro- ( )m
kilo- (k), mega- (M)
Wave velocity for a periodic vibration
Let the wavelength be λand the frequency of the
vibration be f.The wave velocity v is just
V=λ/T, or
V= λf
/Tv
More specifically,
we consider a force acting through a distance.Work = Force x distance or W = F.dUnits - newtons x meters = joules (J), or pounds x feet (foot pounds, ft.lbs)BTU = 778 ft.lbs (energy of one wooden kitchen
match)Pushing on a wall and wall doesn’t move
(no work done on the wall)Conversion: 1J= 0.738 ft.lb
Potential Energy
Energy of position or configuration
Other examples - Springs, bow, sling shot, chemical energy, and gravitational potential energy
The latter is GPE = mgh (the force required to lift at constant speed times the distance )
W
Power = Work/time or P = W/t
Units - J/s =
Watt
2. POWER
550 ft.lb/s = 1
hp
1 hp = 746 J/s = 746 W
1 BTU/hr = 0.293 W
100 W bulb = 0.1341 hp
250 hp engine = 186,450
W
Conditions for standing waves
overpressure
L
Closed tubes(closed on one end)
overpressure
Closed end: antinode
open end:node
L
We define the Sound Intensity I as the Audio Power crossing a unit
area,or I = P/A
Units- W/m2
12-2 Intensity of Sound: Decibels
An increase in sound level of 3 dB, which is a doubling in intensity, is a very small change in loudness.
In open areas, the
intensity of sound diminishes with distance:
However, in enclosed spaces this is complicated by reflections, and if sound travels through air the higher frequencies get preferentially absorbed.
12-2 Intensity of Sound: Decibels
The loudness of a sound is much more closely related to the logarithm of the intensity.
Sound level is measured in decibels (dB) and is defined:
(12-1)
I0 is taken to be the threshold of hearing:
12-2 Intensity of Sound: Decibels
The intensity of a wave is the energy transported per unit time across a unit area.
The human ear can detect sounds with an intensity as low as 10-12 W/m2 and as high as 1 W/m2.
Perceived loudness, however, is not proportional to the intensity.
12-3 The Ear and its Response; LoudnessThe ear’s sensitivity varies with frequency. These curves translate the intensity into sound level at different frequencies.
Note span Interval Frequency ratioC - C unison 1/1C - C# semitone 16/15C - D whole tone (major second) 9/8C - D# minor third 6/5C - E major third 5/4C - F perfect fourth 4/3C - F# augmented fourth 45/32C - G perfect fifth 3/2C - G# minor sixth 8/5C - A major sixth 5/3C - A# minor seventh 16/9 (or 7/4)C - B major seventh 15/8C3 - C4 octave 2/1C3 - E4 octave+major third 5/2
Intervals12-tone scale (chromatic) 8-tone scale (diatonic)
Pythagorean ScaleBuilt on 5ths
A pleasant consonance was observed playing strings whose lengths were
related by the ratio of 3/2 to 1 (demo).Let’s call the longer string C, and the
shorter G, and the interval between G and C a 5th
Denote the frequency of C simply by the name C, etc.
The major triad is the basis for the just scale, which we now develop
in a way similar to that of the Pythagorean scale.
We wish to make a chromatic scale- 12 tones including both octaves- and we want all the
intervals (ratios of adjacent notes to all be the same).
Beats
f1-f2 = beat frequency
Average frequency “heard” = (f1+f2)/2
Modes
• Ionian – Major Scale• Dorian – 2nd of Major Scale• Phrygian – 3rd of Major Scale• Lydian – 4th of Major Scale• Mixolydian – 5th of Major Scale• Aolian – 6th of Major Scale (Minor)• Locrian – 7th of Major Scale
Non-Western Scales
Resonance
Fourier SynthesisDemo- PhET (Physics,Fourier)
String Instruments
The Vocal Tract
epiglottis
Vocal Formants
“had”
To calculate T, consider a room with a hole in one wall of area A.
Call the reverberation time T.T ˜ volume V, 1/A
T= K V/AIt has been worked out that, for V in
m3 , A in m2
T= 0.16 V/A
Let us now replace the open window area with an absorbing
material of area S and absorption coefficient a.
Then A= Sa. If there is more than one type of absorbing material, the
A= S1 a1+s2a2 +S3a3+…
Basic Analog Electronics
Ohm’s Law Links: Bob Holtzworth part 1 slides 1-
11,12,16
Ohm’s LawThe current (charge per unit time)
flowing through a circuit element is equal to the potential drop across
this element divided by the resistance of the element.
I= V/R
Digital Electronics
Introduction to Binary Numbers
We can write the number 752 as2x100 + 5x101 + 7x102
SimilarlyWe could use the base 2, e.g.
3 = 1x20 + 1x21, which we represent as 11.
Hence 01 is 2
These are 2-binary digit (bit) numbers.
Digital Sampling
Calculating Bit-rates (CD quality)
Sampling Rate
x Resolution x# of
Channels= Bit-rate
44,100 x 16 x 2 = 1,411,200
Calculating File Sizes (one minute of CD audio)
Sampling Rate
x Resolution x Number of Channels x Time in
Seconds /
Bits /
Byte = File Size(in Bytes)
44,100 x 16 x 2 x 60 / 8 = 10,584,000
MP3 compression at 128 kbps compresses this by a factor of 11
MP 3 Compression
The most important principle in MP3 compression is the psychoacustic selection of sound signals to cut away. Those signals, we are unable to hear are removed. These include weaker sounds that are present but are not heard because
they are drowned out (masked) by louder instruments/sounds.
Many encoders use the fact that the human ear is most sensitive to midrange sound frequencies (1 to 4 KHz). Hence
sound data within this range is left unchanged. An other compression used is to reduce the stereo signal into
mono, when the sound waves are so deep, that the human ear cannot register the direction. Also the contents of common
information in the two stereo channels is compressed. The Huffman algorithm reduces the file size by optimizing the
data code for the most often used signals. This is a lossless compression working within the MP3 system.
More on CDs
750 Mbytes
75 minutes of audioLink: “how Edison got his groove back”
The elongated bumps that make up the track are each 0.5 microns wide, a minimum of 0.83 microns, they look something like this: