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

--- Quote from: Mechatrommer on November 12, 2023, 05:30:12 pm ---
--- Quote from: wasedadoc on November 10, 2023, 10:38:40 pm ---
--- Quote from: Mechatrommer on November 10, 2023, 07:08:21 pm ---right! playing with sim tonight to design 3rd order elliptic filter (analog/physical) filter (about 60MHz cutoff)... no gibbs effect on sim. so there must be a special one to build a physical filter that can cause "gibbs like" effect. fwiw..

--- End quote ---
Can you plot the phase versus frequency?

--- End quote ---
i just got home, see attached. not sure what it tells. but anything larger than 40MHz is more than 180deg phase?

--- End quote ---
To see if linear phase or not, plot both axes as linear, not log frequency.

Large phase angles per se are not necessarily a problem.  Think about it.  To preserve wave shape all frequencies must be delayed by the same amount of time.   That means phase angle increases linearly with frequency.  Going past 180 or even past 360 degrees is not an automatic no-no.
Mechatrommer:

--- Quote from: wasedadoc on November 12, 2023, 06:36:35 pm ---
--- Quote from: Mechatrommer on November 12, 2023, 05:30:12 pm ---
--- Quote from: wasedadoc on November 10, 2023, 10:38:40 pm ---Can you plot the phase versus frequency?

--- End quote ---
i just got home, see attached. not sure what it tells. but anything larger than 40MHz is more than 180deg phase?

--- End quote ---
To see if linear phase or not, plot both axes as linear, not log frequency.

Large phase angles per se are not necessarily a problem.  Think about it.  To preserve wave shape all frequencies must be delayed by the same amount of time.   That means phase angle increases linearly with frequency.  Going past 180 or even past 360 degrees is not an automatic no-no.

--- End quote ---
unfortunately tina-ti doesnt have linear scale frequency plot. but eyeballing it, the curvy shape could be linear phase when plotted on linear scale x-axis? here's the group delay plot, so i guess its linear phase up to 3MHz? or with some compromise up to 40MHz? see attached. https://audiojudgement.com/group-delay-explanation-measurement-audio/
ebastler:

--- Quote from: Mechatrommer on November 13, 2023, 05:29:40 am ---unfortunately tina-ti doesnt have linear scale frequency plot.

--- End quote ---

Click the "Log" button in the lower right, next to the "Resolution" entry field.
Mechatrommer:

--- Quote from: ebastler on November 13, 2023, 06:10:02 am ---
--- Quote from: Mechatrommer on November 13, 2023, 05:29:40 am ---unfortunately tina-ti doesnt have linear scale frequency plot.

--- End quote ---
Click the "Log" button in the lower right, next to the "Resolution" entry field.
--- End quote ---
:palm:
mawyatt:
Here's something that folks might find interesting. Gibbs Ears created on DHO824 with SDG2042X AWG utilizing Sinewave and Harmonics feature.

Best,
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