Difference between revisions of "MTD2 class 2"
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=Basic Sound forge Editing= | =Basic Sound forge Editing= | ||
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=HomeWork= | =HomeWork= | ||
Finish Simpsons Project | Finish Simpsons Project |
Revision as of 02:21, 22 December 2005
Contents
Media Theory and Design 2
Week Two
In Class
* More on the Properties of Sound o Wave o Speed o Frequency/Period o Amplitude o Wavelegth * Basic Sound forge Editing Simpsons Project * Start Simpsons
Properties of Sound
* Sound Is a Longitudinal wave * Speed of sound (measured in m/s) * Frequency (measured in Hz) * Period (measured in seconds per cycle) * Wavelength (measured in meters) * Amplitude/Pressure (for this class we will only look at dBs) * Phase (measured in degrees)
Wave
Sound Is a Wave (it needs a medium) Transverse vs. Longitudinal Waves medium
* An intervening substance through which something else is transmitted or carried on.
Longitudinal waves move in the same direction as the wave between 0° and 180° to the direction of the wave.
A sound wave is a longitudinal wave
Transverse waves move at right angles to the direction of the wave.
Water is a transverse wave
Transverse Wave and Logitudinal Waves -applet Waves T/L adding reflection -applet Neither the molecules in the air or those in water actually move along with the wave. Air and water are simply a medium for the wave to pass through.
Speed of Sound
The speed of sound is measured in meters per second.The speed of sound is affected by several factors: temperature, humidity, and elasticity.
~344 m/s or 1130 f/s
NOTE: for class we will assume the speed of sound in air @ 20 degrees Celsius an 75% humididty is 344m/s
Speed of sound Calculator -applet
Frequency/Period
Sound is a periodic event. This means that there is a fixed amount of time between different events.The Frequency component of a sound wave affects the pitch of the sound.
Frequency is measured in Hertz (cycles per second)
Period = 1 / Frequency in HzT = 1/f
Frequency = 1/ Period f = 1/T
Different types of frequency components periodic/ aperiodic
It is assumed the humans can hear frequencies from 20Hz to 20,000 Hz.
20-20KHz Sweep 41k,16 bit 3.7megs Resonance
Tacoma Narrows Bridge Movie1 Movie2
Wavelength
Wavelength is measured in distance (ft. of m)
The actual physical length of a single cycle of a wave
Wavelength = speed of sound / Frequency in Hz
Lambda = C/f
wavelength = speed of sound * period
Lambda = CT The wavelength of a sound wave varies greatly with the frequency of the wave. A 20 kHz wave has a wavelength of 1.72 (0.7 in)cm while a 20 Hz wave has a wavelength of 17.2 m (~56 ft.).
Amplitude/Pressure
Measured in dB (decibels) Decibel Definition all about decibels Decibels
The softest sound we as humans can hear is about 20 micropascals (20µPa or 0 dB re 20µPa ) the loudest sound we as humans can tolerate is about 200 Pa(120 dB re20µPa) this is a 10,000,000:1 ratio. This is why Bel labs decided to use a different scale to represent the numbers. They used the deciBel or 1/10 of a Bel.
decibels as a power ratio The Bel was defined as the logarithm of a power ratio and was named after Alexander Graham Bell. The deciBel is 1/10th of a Bal. Since the range of human hearing is so large a logarithmic scale was implemented because the range of human hearing is os large. Sound Pressure and common sound sources
140 dB SPL | .45 APC Colt pistol (25 ft.) |
130 dB SPL | 50 HP Siren (100 ft.) |
120 dB SPL | Threshold of pain |
110 dB SPL | Typical rock concert |
90-100 dB SPL | Platform of subway station as train arrives. Loud classical music |
80 dB SPL | Person Shouting |
60 dB SPL | Average conversation (5 ft) |
40 - 50 dB SPL | Average suburban home at night |
30 dB SPL | Very quiet whisper |
20 dB SPL | Extremely quiet Recording Studio |
0 dB SPL | Threshold of hearing. Anechoic Chamber |
Ear Illustration Hearing Loss Articles
Decibels (a different way of counting)
Decibels are based on a logarithmic scale.
dB SPL/voltage/current
dB = 10 * log (P12 + P22) = dB = 20 * log (P1 + P2)
1dB small change in power
6dB doubling of power
20 dB roughly twice as loud ten times the voltage
Voltage, current or SPL | dB |
1 | 0.00 |
1.5 | 3.52 |
2 | 6.02 |
2.5 | 7.96 |
3 | 9.54 |
4 | 12.04 |
5 | 13.98 |
6 | 15.56 |
7 | 16.90 |
9 | 18.06 |
10 | 19.08 |
20 | 20 |
30 | 29.54 |
40 | 32.04 |
50 | 33.98 |
100 | 40 |
1000 | 60 |
5000 | 73.97 |
10000 | 80 |
here are some other good explanations
http://ews64.com/mcdecibels.html
Here is a good dB adding calculator
http://www.mcsquared.com/dbframe.htm this site can also do some other neato thangs...
Intro To Sound Forge
Basic Sound forge Editing
Simpsons Project http://interactive.colum.edu/MTD2/assignments/class2/editing1/editing1.html
HomeWork
Finish Simpsons Project Read Sound Design for Interactive Multimedia chapter 1 pg 3 - 31 optional look over sound forge manual (it's in //interactive.colum.edu/classfolders/MTD2)
* chapter 3 - getting started * chapter 4 - navigation zooming and selecting
Review