# Basic Acoustics - PowerPoint PPT Presentation

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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 Acoustics

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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

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

One Cycle

Zero Crossings

### 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

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

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

• Hammond Organ

Sum of two sine wave

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

### 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