This document discusses key concepts related to multimedia and digital multimedia. It defines multimedia as a combination of two or more media forms, with one being discrete and one continuous. Interactive multimedia allows the viewer to control what elements are delivered. Digital multimedia involves digitizing analog signals through sampling and quantization. The Nyquist sampling theorem states the sampling rate must be at least twice the maximum signal frequency to reconstruct it accurately. An analog-to-digital converter is used to convert analog signals to digital for use in digital devices and compression is used to reduce data size. The document also discusses bandwidth ranges for different audio devices and the human ear.

1. Information and Communication
Technologies(ICT)
Principles and Perspectives
Lecture : Distributed multimedia systems

2. Multimedia
• Multi’ means ‘more than one’
• ‘media’ represents the plural of ‘medium’
• Medium: an intermediate agency, instrument, or channel; especially a means
or channel of communication or expression

3. Categories of media
• Continuously in time
• Video belongs to this category ( sequence of video frames)
• Other examples ??
• Continuously in space
• Text is example of this category ( Discrete in nature)
• Other examples ??
• Multimedia is a combination of two or more media, one of which is discrete,
and the other continuous

5. Interactive multimedia
• when a viewer of a multimedia presentation is allowed to control what
elements are delivered and when, it is interactive multimedia.

6. Digital multimedia
• Digitization
• Analogue Vs Digital
• Continuous signal is analogue like electricity
• Computer understands binary so we have to convert analogue into digits
• This process is known as digitization

7. Digital multimedia
• Sampling
• taking samples of the continuous signal. The number of samples taken during a time
period is known as the sampling rate.
• Quantization
• restrict the value of the samples to a fixed set of levels. The unit of sampling rate is
Hertz (Hz), i.e. 1Hz means taking one sample per second. We use KHz

8. Nyquist sampling theorem
• In order to reconstruct the signal, the sampling rate must not be less than
twice the maximum frequency of the original signal
• Under sample aliasing
• quantization error if few quantization levels

9. Analogue-to-digital converter
• a digital camera or a scanner
• a digital audio recorder
• a digital camcorder.
• Data size issue, compression

10. Sound
caused by vibration of material
pressure wave fluctuations in the air
move hair-like fibers in ear
electrical impulses sent to the brain
Brain coverts them to auditory sensations

11. Bandwidth
Bandwidth is the range of frequencies a device can produce or a human can hear
• FM radio 50 Hz – 15 kHz
• AM radio 80 Hz – 5 kHz
• CD player 20 Hz – 20 kHz
• Sound Blaster 16 sound card 30 Hz – 20 kHz
• Inexpressive microphone 80 Hz – 12 kHz
• Telephone 300 Hz – 3 kHz
• Children’s ears 20 Hz – 20 kHz
• Older ears 50 Hz – 10 kHz
• Male voice 120 Hz – 7 kHz
• Female voice 200 Hz – 9 kHz.