Multimedia Systems WS 2010/2011 08.11.2010 M. Rahamatullah - - PowerPoint PPT Presentation

University of Kaiserslautern Department of Computer Science Integrated Communication Systems ICSY http://www.icsy.de

Multimedia Systems

WS 2010/2011 08.11.2010

• M. Rahamatullah Khondoker (Room # 36/410 )

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• M. Rahamatullah Khondoker, University of Kaiserslautern

Outline

 Data and Signals

 Signal Basics

 Digitization

 Sampling  Quantization  Encoder

 Decibels

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• M. Rahamatullah Khondoker, University of Kaiserslautern

Data and Signals

 Analog data: continuous and takes continuous values

 Examples: speech, analog clock, hands movement

 Digital data: have discrete states and takes discrete values

 Examples: digital clock

 Analog signal: has infinite number of values in a range  Digital signal: have limited number of values

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• M. Rahamatullah Khondoker, University of Kaiserslautern

Signal Basics

 Signals can be periodic or non-periodic  Period (T): time (in second) of one cycle  Frequency (f): number of periods in 1 second  Frequency (f) and periods (T) are inverse to each

• ther

 Peak Amplitude (A): absolute value of its highest intensity

• Fig. Example of periodic signals

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• M. Rahamatullah Khondoker, University of Kaiserslautern

Signal Basics

 Phase: position of the signal relative to time 0

• Fig. Examples of different

phases of signal

• Fig. Examples amplitudes, frequencies

and phase

Digitization

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• M. Rahamatullah Khondoker, University of Kaiserslautern

Digitization

 Digitization is the process of creating digital data from analog signal  Steps

 Sampling  Quantizing  Encoding

 Examples encoder

 Pulse Code Modulation (PCM)  Delta Modulation

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• M. Rahamatullah Khondoker, University of Kaiserslautern

Sampling

 Capture continuous signal in a discrete interval  Nyquist–Shannon sampling theorem A signal with a maximum frequency (Nyquist-Frequency, Grenzfrequenz) fmax has to be sampled with a minimal frequency of fa=2*fmax to allow an accurate reconstruction of the original signal.

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• M. Rahamatullah Khondoker, University of Kaiserslautern

Sampling

 signal with fs=200 Hz

1 100

• ----- s

Amplitude Time

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• M. Rahamatullah Khondoker, University of Kaiserslautern

Sampling

 signal with fs=200 Hz  sampling rate of fa=300 Hz  Maximum frequency of chosen sampling rate is fg = fa/2 = 150 Hz

1 100

• ----- s

Amplitude Time

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• M. Rahamatullah Khondoker, University of Kaiserslautern

Sampling

 signal with fs=200 Hz  sampling rate of fa=300 Hz  Maximum frequency of chosen sampling rate is fg = fa/2 = 150 Hz  Reconstruction results in a the signal with fr = 100 Hz

1 100

• ----- s

Amplitude Time

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• M. Rahamatullah Khondoker, University of Kaiserslautern

Sampling

1 100

• ----- s

Amplitude Time Frequency (Hz)

fg fs fr Time Domain Frequency Domain

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• M. Rahamatullah Khondoker, University of Kaiserslautern

Sampling

 Oversampling

 Theoretically no advantages  Usage scenario: Non-optimal filters

• Ideal vs. real low-pass filter

 Disadvantages

• no quality gain
• more storage space & higher data rates are required

 Undersampling

 Signal cannot be reconstructed

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• M. Rahamatullah Khondoker, University of Kaiserslautern

Quantization

 Transform signal with continuous values into a signal with discrete values

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• M. Rahamatullah Khondoker, University of Kaiserslautern

Quantization Error

 Occurs when the approximated value is not equal to the real value  Low quantization error

 Low bit rate and low storage consumptions  High quality

 High quantization error

 High bit rate and high storage consumptions  Low quality

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• M. Rahamatullah Khondoker, University of Kaiserslautern

Pulse Code Modulation

 PCM has

 PAM Sampler  Quantizer  Encoder

 PAM sampler makes PAM pulses  Quantizer constitutes PCM pulses  Encoder provides digital data

Decibel

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• M. Rahamatullah Khondoker, University of Kaiserslautern

Decibel

 Signals lost or gained strength is measured by using decibel  Relative strength of two signals or one signal at different points  A specification in decibel is always related to a reference value!  Decibels can be added or subtracted when we are measuring several points instead of two

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• M. Rahamatullah Khondoker, University of Kaiserslautern

Decibel

 dB(SPL)



• ften simplified: dB

 sound pressure level

• Measurement unit: pascal (Pa)
• relative to 20 micropascals (μPa) = 2×10−5

Pa

 dB(A), dB(B), dB(C), dB(D)

 unit adapted to the sound level perception

• f human hearing

 A-, B-, or C-Filter for weighting

 dBm, dBmW

 electrical power

• Measurement unit: milliwatt
• Relative to 1 milliwatt

 dBi

 Transmission power of antennas

• Relative to hypothetical perfect isotropic

antenna

Thanks for your attention Any questions, comments or concerns?

Integrated Communication Systems ICSY University of Kaiserslautern Department of Computer Science P.O. Box 3049 D-67653 Kaiserslautern

• M. Rahamatullah Khondoker, M.Sc.

Phone: +49 (0)631 205-26 43 Fax: +49 (0)631 205-30 56 Email: khondoker@informatik.uni-kl.de Internet: http://www.icsy.de