MTD2 class 2
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
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
Week1
Week3