OCSC 2315

2

Multimedia

• Analog signal is

continues and the amplitude changes with time.

• Digital signal varies between two discrete values high(1) and low

(0).

3

Multimedia

• Digital Music Concepts

• Sound Signal: A pattern or variation in the motion of air

molecules that a sound makes.

• Microphone: A device that converts sound energy into electrical signal.

• Loudspeaker: A device that converts electrical signal into sound energy.

• Electrical signals representing sound are analog or continuous. To represent these signal in the digital form, we need to convert an analog to signal to a digital signal.

4

Multimedia

• Analog signal can

converted to a digital signal by sampling the signal at discrete intervals of time. In order to preserve the information, the signal must be samples at least by Nyquist rate, which is a minimum sampling rate needed that is equal to twice the bandwidth of the analog signal.

5

Multimedia

• For example

bandwidth of a telephone signal is

3.5Hz. The sampling rate required for the signal is 7000 samples per second.

• The equation for a sinusoidal signal is shown to the right.

S t A sin 2 ft where A Amplitutde f Frequency

3.142

1

T period f 6

Digital Image and Video

• An image can be represented by a continuous function f(x,y), where

f(x,y) is a gray value at (x,y). The image can be digitized by sampling at mxn discrete array points. The sampling interval is determined by the sampling theorem.