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Sub: Rigol's DHO800 Oscilloscope (Gibbs Effect & Aliasing Misunderstanding)
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Fungus:

--- Quote from: tautech on October 27, 2023, 01:00:09 am ---At 5ns/div what do you see 400ps before the rising edge ? Zip, zero, nada !

--- End quote ---

Yep, and that's exactly what I want when I've got a good sample rate to bandwidth ratio (ie. with a single channel enabled).

Would I like a sharper, Siglent-like bandwidth rolloff when I turn on more channels and the ratio changess? Yes, but I can't have everything.

That's the dilemma... the choice a manufacturer has to make when they design an oscilloscope front end.  :-//
Mechatrommer:

--- Quote from: tautech on October 27, 2023, 12:04:07 am ---From Leo's website a capture from a fast Tek clearly displaying the Gibbs ears other scopes choose to suppress.

--- End quote ---
1) gibbs ears are not "after the EVENT" (rising or falling edge), gibbs ears are before the "EVENT".
2) although overshoot and undershoot after the "EVENT" are similar (symetric) appearance. thats why its easily confused, if not read carefully.
2) overshoot and undershoot are real, gibbs ears are not...
3) overshoot and undershoot are "causal" phenomena, caused by the rising and falling EVENT, gibbs ears, if it really exist in reality, are "non-causal"
4) gibbs ear are fabricated in mathematical post processing in DSP IC due to imperfect (not infinite) terms sinc interpolation.
5) you yourself demonstrated the gibbs ear by showing 2c captures, one is using X, another is sinc interpolation, but it turned out you are looking at the wrong side (the actual post-event) of "gibbs ear"

you have similar confusion as Fungus who are mistakenly identify Gibbs ear as aliasing, thats why we keep reacting round and round... here again, on the correct side (the unrealistic, the DSP fabricated) of the gibbs ear i was talking about. not the other side...



here again (attached) i should have provided more proper picture, i thought i was clear enough (my mistake). and esp to sales representative need to get this right. cheers ;)

Mechatrommer:

--- Quote from: Fungus on October 27, 2023, 12:04:31 am ---There's a simple way to know if you're seeing aliasing: Turn some channels off and see if the displayed waveform changes.
(assuming you're not STOPped...)

--- End quote ---
aliasing is false low freq representation of actual high frequency element above nyquist/2.5 leo bodnar test shows no high frequency ringing, so no, i dont see any aliasing. either you look at the wrong side, or misinterpret DSP math post-processing with aliasing. aliasing will not caused non-causality... the picture you showed, is math post-processing, unless you can give better proof, fwiw..
Fungus:

--- Quote from: Mechatrommer on October 27, 2023, 05:32:10 am ---4) gibbs ear are fabricated in mathematical post processing in DSP IC due to imperfect (not infinite) terms sinc interpolation.

--- End quote ---

Nope.

A pulse is the sum of a load of sine waves (infinite). Gibbs ears are caused by some of those sine waves being missing.

(because 'scopes have finite bandwidth)
ebastler:

--- Quote from: Fungus on October 27, 2023, 06:04:03 am ---
--- Quote from: Mechatrommer on October 27, 2023, 05:32:10 am ---4) gibbs ear are fabricated in mathematical post processing in DSP IC due to imperfect (not infinite) terms sinc interpolation.

--- End quote ---

Nope.

--- End quote ---

Thanks. And actually it's "nope" to most of the other statements in Mechatrommer's list of claims in that post. But I think we have already beaten this to death here and this discussion is going nowhere.

Could we all agree that the DHO800 pulse response is fine, and go back to the scheduled program?

(Edit: For clarity, I consider the Siglent pulse response fine as well. But that is the controversy over the past X pages of the thread, and the part where I think the discussion with Mechatrommer is not getting anywhere. And it is off-topic in a "DHO800 unbox and teardown" thread.)
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