Www.kostic.niu.edu © MMIII* Prof. M. Kostic Sampling and Aliasing: An Interactive and On-Line...

© MMIII* Prof. M. Kosticwww.kostic.niu.edu

Sampling and Aliasing:Sampling and Aliasing:An Interactive and On-Line An Interactive and On-Line

Virtual ExperimentVirtual Experiment

""What We See is Not What It Is!What We See is Not What It Is!""

Prof. M. KosticProf. M. Kostic Mechanical EngineeringMechanical Engineering

NORTHERN ILLINOIS UNIVERSITYNORTHERN ILLINOIS UNIVERSITY


What are “What are “samplingsampling” ” and “and “aliasingaliasing” ?” ?

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).


W.W.S.W.W.S.N.N.W.I.I.W.I.I. ""What We See What We See is Notis Not What It Is! What It Is!""

It’s all about ...It’s all about ...… … Sampling and AliasingSampling and Aliasing!!

Even ...Even ...W.Y.S.W.Y.G.W.Y.S.W.Y.G. ""What You See is What You Get!What You See is What You Get!””

……is REALLY NOT true (the same)is REALLY NOT true (the same) on different Monitors and Printerson different Monitors and Printers


Signal/Sampling ResolutionSignal/Sampling Resolution

SamplingSampling//Time Resolution Time Resolution ((SpeedSpeed))

Sig

nal

Sig

nal

// Mag

nit

ud

e M

agn

itu

de

Res

olu

tion

Res

olu

tion


There is NOThere is NOsuch thing as...such thing as...……too large hard drive disk, too large hard drive disk, or ...or ...……too large sampling resolutiontoo large sampling resolution!!

Well praised ... Well praised ... high-definition digital graphicshigh-definition digital graphicsand CD-quality musicand CD-quality music

……are NOT good (true) enoughare NOT good (true) enough!!


• Under-sampling Under-sampling looseslooses (important) wave (important) wave detailsdetails !!

• But it also But it also may changemay change the wave the wave form/shapeform/shape due to Aliasing due to Aliasing !!

((UnderUnder))Sampling & Aliasing ...Sampling & Aliasing ...


Real measurements Real measurements of a simple sine-harmonicof a simple sine-harmonic

How come this if the measured signalis a simple sine-harmonic wave?


Sampling-Beat WaveSampling-Beat Wave

Sampled signal

Real signal


Good SamplingGood Sampling

Sampled signal

Real signal


Sampling with AliasingSampling with Aliasing

Sampled signal

Real signal


Stroboscope light Rotating disk(RPM)

Sampling RPM with StroboscopeSampling RPM with Stroboscope

If RPM and Strobe speeds(frequencies) are the same

the reference mark willappear stationary (ZERO aliasing)

If the Strobe speed is fasterIf the Strobe speed is slower

If the Strobe speeds ishalf of RPM, the disk willturn twice and the mark

will appear stationary again!


Folding DiagramFolding Diagram

NO

Ali

as. Aliasing

ZEROAliasing


Sampling and Aliasing…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.


Sampling and Aliasing…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.


Interactive Experiments ...Interactive Experiments ...

LabVIEW Virtual InstrumentsLabVIEW Virtual Instruments

Internet Interactive ExperimentInternet Interactive Experiment

Animated MovieAnimated Movie


The Art of Sampling and AliasingThe Art of Sampling and Aliasing

Real signal

Sampled signal

MAGNITUDE Ratio

PHASE Shift


Conclusion…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…


Conclusion…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”!.


Who does the future belongs to ?Who does the future belongs to ?

??


No Limits …No Limits …

The Future The Future Belongs Belongs

To…To…

… … Whoever Whoever Gets There Gets There

FirstFirst

NOSPEED

LIMIT


You may contact Prof. Kostic at:You may contact Prof. Kostic at:

mailto:mailto:[email protected]@niu.eduor on the Web:or on the Web:

www.kostic.niu.eduwww.kostic.niu.edu

http://http://prof.mkostic.comprof.mkostic.comProf. M. KosticProf. M. Kostic

Mechanical EngineeringMechanical Engineering

NORTHERN ILLINOIS UNIVERSITYNORTHERN ILLINOIS UNIVERSITY

Www.kostic.niu.edu © MMIII* Prof. M. Kostic Sampling and Aliasing: An Interactive and On-Line...

Documents

Transcript of Www.kostic.niu.edu © MMIII* Prof. M. Kostic Sampling and Aliasing: An Interactive and On-Line...