Definition: Aliasing
Definition: Aliasing
(OP)
Hi All,
I know what aliasing is and many times I need to explain it to a layman or engineer for that matter that doesn't understand vibration, etc.
Does anyone have a good explanation in layman's terms for aliasing?
Thanks in advance for your help!
I know what aliasing is and many times I need to explain it to a layman or engineer for that matter that doesn't understand vibration, etc.
Does anyone have a good explanation in layman's terms for aliasing?
Thanks in advance for your help!
Frank Lucca M.I.Exp.E.
www.terradinamica.com





RE: Definition: Aliasing
it is a problem that arises when the data is collected at regular intervals and it is converted into amplitude(and phase) format as a function of frequency. it shows up as spurious frequency content when the rate of sampling is comparable to the rate that the data itself is changing.
RE: Definition: Aliasing
When sampled below the Nyquist frequency, a sampled signal will exhibit "aliased" frequencies that were ambiguously recovered as lower values than they were in the original signal.
Mathematically, sampling results in multiple copies of the signal spectrum in frequency spaced at the sampling frequency. If spectra overlap, as with undersampled signals, the higher frequency content is "folded over" into a lower frequency range, thereby causing "aliasing"
TTFN
RE: Definition: Aliasing
Draw a sinusoid, then look at the location of samples for:
5 samples per period of the sinusoid
2.1 samples per period of the sinusoid
1.9 samples per period of the sinusoid
At 2.1 samples per period if you connect the dots you will see the original sinusoid.
At 1.9 samples per period the distance between samples is more than 1/2 a period. Connect the dots of your samples and it forms a sinusoid at lower frequency than the one you were sampling. That is aliasing.
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RE: Definition: Aliasing
RE: Definition: Aliasing
Skip Hartman
http://www.machinerywatch.com
RE: Definition: Aliasing
Thanks guys, that's what I was looking for. Sometimes its hard not to be an engineer. When we are speaking to layman, this is especially true.
In rock blasting, if we set up monitoring stations to close to a blast, aliasing occurs and screws up all the data. I'm continually trying to explain this to other engineers and regulators that do not understand much about vibration.
Best regards,
Frank Lucca M.I.Exp.E.
www.terradinamica.com
RE: Definition: Aliasing
Imagine that the analog time waveform consists of very short impacts with lots of lower-magnitude ringing-down or “dead” time between impacts.
http://reliability-magazine.com/pub/CARS12TWF.jpg
The sharp rise time of the peaks represents high frequency content. Therefore we need high sample rate.
The picture here has high sample rate and shows the peaks.
If the sample rate was lower you would likely not sample on the peak. The peak won’t look as high in relation to the other stuff. The character of the waveform changes.
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RE: Definition: Aliasing
It is harder to propagatehigh frequencies in air, so the farther you are from the blast, the fewer high frequencies encountered
TTFN