EE4209/EE5809 Digital Audio Technology

EE4209/EE5809 Digital Audio Technology

Notes : quoted from "The Science of Digital Media"
chapter 1

1. sound is a one-dimensional function -- that is, a function with one variable as input. if we think of sound as a continuous phenomenon, then we can model it as a continuous
function y= f (x) where x is time and y is the air pressure amplitude.

2. Let r be the size of an angle measured in radians, and let d be this size measured in degrees. then,

r/d = PI/180

we say " a simple sine wave " when we wish to emphasize that it is a single function rather than of two or more.

3.sound is " mechanical wave " , which means that it results from the motion of particles through a transmission wave,
it has to have something to move through, sound cannot be transmitted through a vacuum.

The movement associated with a sound wave is initiated by a vibration.

4. The motion of the air molecules is back and forth from left to right, the same direction in which the wave in which the motion of individual particles is parallel to the direction in which energy is being transported.

Sound is a longitudinal mechanical wave.

5. A wave is said to be periodic if it repeats a pattern over time. the pattern that is repeated constitutes one cycle of the wave.

A " wavelength " is the LENGTH ( in distance ) of ONE complete cycle.

The " frequency " of a wave is the NUMBER of times a cycle repeats per unit time, which in the case of sound corresponds to the rate at which the air molecules are vibrating.

The frequency of a sound wave is measured n cycles per sound or Hertz.

The PERIOD of a wave is the amount is the amount of time it takes for ONE cycle to complete. Period and frequency are reciprocals of each other.

Let T be the period and f be the frequency of a sinusoidal wave. Then, T = 1/f and f = 1/T.

The height of a wave is called its amplitude.

6. To create a sine function representing a sound wave frequency f HZ, you must convert f to " angular frequency " first.

Let f be the frequency of a sine wave measured in Hz. Let w be the equivalent angular frequency measured in radians/s.

then w = 2 PI *f

7. the amplitude of a wave corresponds to how loud the sound is. The frequency of a wave corresponds to the pitch of the sound.

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