MULTIMEDIA
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.