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Basic Acoustics. Basic Acoustics. Sound – your ears’ response to vibrations in the air. Sound waves are three dimensional traveling in all directions. Think of dropping a pebble into a pool of water. Sound can be directional

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Basic acoustics1
Basic Acoustics

  • Sound – your ears’ response to vibrations in the air.

  • Sound waves are three dimensional traveling in all directions. Think of dropping a pebble into a pool of water.

  • Sound can be directional

  • Air molecules themselves don’t move very far, instead transferring energy to nearby molecules


Sound wave
Sound Wave

One Cycle

Zero Crossings


Wave properties
Wave Properties

  • Frequency

    • Cycles per second

    • Hertz (Hz)

    • Perceived as Pitch

  • Amplitude

    • Amount of air being displaced

    • Measured in decibels (dB)

    • Perceived as Volume


Timbre
Timbre

Harmonic Series

  • Timbre is defined by the harmonic content

  • Overtones are present to some degree in all sound except sine waves

  • Lowest frequency is the fundamental

  • Each tone is called a harmonic or partial

  • Doubling a partial number results in a pitch one octave higher

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16


Fourier theorem
Fourier Theorem

  • Any periodic complex wave can be broken down into sine wave components

  • Basis of additive synthesis

    • Hammond Organ

Sum of two sine wave

http://en.wikipedia.org/wiki/Joseph_Fourier


Basic waveforms
Basic Waveforms

Sine Wave – fundamental only

Triangle Wave – odd partials amplitude = 1/n2

Sawtooth Wave – all partials

Amplitude = 1/n

Square Wave – odd partials

Amplitude = 1/n


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