1. www.kostic.niu.edu © MMIII* Prof. M. Kostic Sampling and Aliasing: An Interactive and On-Line Virtual Experiment Sampling and Aliasing: An Interactive and On-Line Virtual Experiment " What We See is Not What It Is! " Prof. M. Kostic Mechanical Engineering Mechanical Engineering NORTHERN ILLINOIS UNIVERSITY

2. www.kostic.niu.edu © MMIII* Prof. M. Kostic What are “sampling” and “aliasing” ? Figure 2: The aliasing examples: “wagon wheel illusion,” appearance that a spoke wheel rotates backward while it moves forward (left); a stroboscope experiment to “freeze” rotating fan blades or to make them appear to move slowly forward or backward (center); and appearance of staircase steps along edges (jaggies) in an image (right).

3. www.kostic.niu.edu © MMIII* Prof. M. Kostic W.W.S.N.W.I.I. " What We See is Not What It Is! "  It’s all about... … Sampling and Aliasing !  Even...W.Y.S.W.Y.G. " What You See is What You Get! ”  …is REALLY NOT true (the same) on different Monitors and Printers

4. www.kostic.niu.edu © MMIII* Prof. M. Kostic Signal/Sampling Resolution Sampling/Time Resolution (Speed) Signal / Magnitude Resolution

5. www.kostic.niu.edu © MMIII* Prof. M. Kostic There is NO such thing as...  …too large hard drive disk, or...  …too large sampling resolution!  Well praised... high-definition digital graphics and CD-quality music  …are NOT good (true) enough!

6. www.kostic.niu.edu © MMIII* Prof. M. Kostic Under-sampling looses (important) wave details !Under-sampling looses (important) wave details ! But it also may change the wave form/shape due to Aliasing !But it also may change the wave form/shape due to Aliasing ! (Under)Sampling & Aliasing...

7. www.kostic.niu.edu © MMIII* Prof. M. Kostic Real measurements of a simple sine-harmonic How come this if the measured signal is a simple sine-harmonic wave?

8. www.kostic.niu.edu © MMIII* Prof. M. Kostic Sampling-Beat Wave Sampled signal Real signal

9. www.kostic.niu.edu © MMIII* Prof. M. Kostic Good Sampling Sampled signal Real signal

10. www.kostic.niu.edu © MMIII* Prof. M. Kostic Sampling with Aliasing Sampled signal Real signal

11. www.kostic.niu.edu © MMIII* Prof. M. Kostic Stroboscope light Rotating disk (RPM) Sampling RPM with Stroboscope If RPM and Strobe speeds (frequencies) are the same the reference mark will appear stationary (ZERO aliasing) If the Strobe speed is faster If the Strobe speed is slower If the Strobe speeds is half of RPM, the disk will turn twice and the mark will appear stationary again!

12. www.kostic.niu.edu © MMIII* Prof. M. Kostic Folding Diagram NO Alias. Aliasing ZERO Aliasing

13. www.kostic.niu.edu © MMIII* Prof. M. Kostic Sampling and Aliasing… Sampling is a discrete observation or measurement, while Aliasing is an illusion, appearance of something that is NOT, due to shortcomings of sampling, …thus everything we perceive or measure is, to a lesser or grater degree, an ILLUSION, responsible for many discoveries and re-discoveries in invention history.

14. www.kostic.niu.edu © MMIII* Prof. M. Kostic Sampling and Aliasing… Even if we are not interested in those high-frequency signal components, the problem is that they may “fold- back” and falsely appear as low- frequency components that do not exist in reality at all, thus trick us. Such phenomena are well-known as aliasing, which is actually an illusion.

15. www.kostic.niu.edu © MMIII* Prof. M. Kostic Interactive Experiments... LabVIEW Virtual Instruments LabVIEW Virtual Instruments Internet Interactive Experiment Internet Interactive Experiment Animated Movie Animated Movie

16. www.kostic.niu.edu © MMIII* Prof. M. Kostic The Art of Sampling and Aliasing Real signal Sampled signal MAGNITUDE Ratio PHASE Shift

17. www.kostic.niu.edu © MMIII* Prof. M. Kostic Conclusion… This interactive module will stimulate users’ curiosity and motivate them to conveniently “check out” different options and possibilities, and thus accelerate experience and by active, what-if inquiry and “experimentations” enhance their comprehension and interest for deeper thinking and understanding…

18. www.kostic.niu.edu © MMIII* Prof. M. Kostic Conclusion… These new learning tools are not and cannot replace the traditional learning by cognitive thinking, but, if designed well, the new simulation tools may qualitatively enhance learning environment by stimulating inquiry and building confidence and motivation – in short, may become a “virtual eye and mind opener”!.

19. www.kostic.niu.edu © MMIII* Prof. M. Kostic Who does the future belongs to ? ?

20. www.kostic.niu.edu © MMIII* Prof. M. Kostic No Limits … No Limits … The Future Belongs To… … Whoever Gets There First NO SPEED LIMIT

21. www.kostic.niu.edu © MMIII* Prof. M. Kostic You may contact Prof. Kostic at: mailto: kostic@niu.edu mailto: kostic@niu.edu or on the Web: www.kostic.niu.edu www.kostic.niu.edu http:// prof.mkostic.com http:// prof.mkostic.com Prof. M. Kostic Mechanical Engineering Mechanical Engineering NORTHERN ILLINOIS UNIVERSITY