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Basic Acoustics

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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

- Frequency
- Cycles per second
- Hertz (Hz)
- Perceived as Pitch

- Amplitude
- Amount of air being displaced
- Measured in decibels (dB)
- Perceived as Volume

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

- 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

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