Three Components of Sound

Pitch Loudness and Timbre

Pitch


Pitch is determined by how many times a sound wave repeats itself within one second of time.

  • Each repetition of a waveform is called a cycle.
  • The number of repetitions that occur per second is called the frequency.
  • Frequency is measured as cps = cycles per second or in Hz called hertz. “Hz” is derived from the name of Heinrich Hertz, a German scientist who did pioneering work in electromagnetic waves during the 19th. Century.

WAVELEN.GIF


The Closer the peaks are together, the higher the pitch.
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Human have a finite range of hearing

20 Hz to 20,000 Hz (20 kHz)
Ringtone Audible Only to Under-20 Year Olds
May 24, 2006 by Vurdlak

Wow!!! This has to be the coolest audio illusion of all times! Apparently, using the Mosquito device, UK pupils have recorded the ultra-high sound that is audible only to under-20-year-olds. Your hearing gets progressively worse around the age of 20, so if you play a sound on the edge of your hearing spectrum, unless you have perfect hearing, you won't be able to hear it at all. As I understood, the audio file is somewhere between 18KHz - 20KHz. When I played it, I haven't heard anything, and thought it was just another internet hoax, but then my 14 year old brother started yelling at me, to lower that sound cause it's driving him crazy - and he was in lower apartment!! Another thing.. my dog also flipped out! Here are some of these files. Check them out and report your findings!






Loudness


  • The relative strength of the deviations in air pressure created by a vibrating object determines the loudness (or volume).
  • The greater variations in air pressure, the louder we perceive the sound.
  • These deviations are referred to as the amplitude of the waveform

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The intensity level of a sound is measured in a unit known as the decibel (or dB). A unit of measurement named after Alexander G. Bell, who invented the telephone. The use of the capital “B” in the abbreviation is in his honor.


•The softest sound that a person can hear-the threshold of hearing”- is defined as 0dB.
•The “threshold of pain” is about 120 dB.

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Timbre

(tam-ber)

Harmonics Applet
Why does a flute sound different than a clarinet when they play the same note?
The number of harmonics present in their sound, and the relative amplitude of each harmonic.

  • The property of a sound that allows us to determine the difference between a saxophone and a flute is called timbre, or tone color.
  • Different timbres occur because most sounds actually contain many frequencies.
  • The predominant pitch is called the fundamental frequency of the sound. The other frequencies present occur in a mathematical series called the harmonic series, or overtone series.
  • The frequency of each harmonic is a whole number multiple of the fundamental frequency. (i.e.; 2x,3x,4x, etc..)

When a string vibrates to create a sound, it has several compressions and rarefactions occurring simultaneously.


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The amplitude of each harmonic determines the timbre of the sound.

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Creating different timbres electronically

Different timbres result in different shapes in the plotted waveform. Certain waveforms(and consequently certain timbres) have long been used a building blocks of synthesis.


A sine wave consists of only the fundamental. No other harmonics are present.
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A square wave consists of only the odd harmonics.
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A triangle wave consists of only the odd harmonics, however there is a decrease in amplitude of the upper harmonics.

Like a square wave, the triangle wave contains only odd harmonics. However, the higher harmonics roll off much faster than in a square wave (proportional to the inverse square of the harmonic number as opposed to just the inverse), and so its sound is smoother than a square wave and is nearer to that of a sine wave.

external image 350px-Synthesis_triangle.gif






A Sawtooth wave consists of all harmonics.

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external image 400px-Waveforms.svg.png

WAVESHAPES


All Frequencies combined create NOISE.



Most natural sounds form complex waves.

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A moving sound object will catch up to itself... the waves then get closer together thus producing a higher pitch.
This is known as the Doppler Effect.
external image Doppler_effect.jpg



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