With fast edges (or what ever waveform) as example rectangle/square wave. Corners "wobbling" is just aliasing because some harmonics in signal goes over Nyquist wall. (or better say, too near it).
With perfect sampling, the sinc filtering of a fast edge should only produce the Gibb's phenomena which is phase coherent with the input signal and looks like preshoot and overshoot. I think the actual "wobulation" sometimes seen is caused by intermodulation distortion in the digitizer which results in additional frequency spurs which are also aliased. In both cases, increasing the sample rate or bandwidth limiting the input signal helps.
I have not seen any entry level or bit over this level new digital scope what have acceptable analog side filter system. Still they design front ends like in cheap analog scopes where slow decaying gaussian BW shape is fully ok.
It is not ok in digital scopes in real time "one shot" sampling mode. (ETS is different - but only for repetitive signals). It looks like digital peoples are designing oscilloscopes and no one really care about analog front end before ADC.
Some of the very early Tektronix DSOs included four pole 24dB/octave Gaussian filters which should have helped with this but I do not know if their unfiltered input bandwidth also had a 4 pole Gaussian response. On an analog oscilloscope it hardly matters except for noise measurements.
Same can see in some scopes what have 50ohm input. Not even close real 50ohm impedance, exept with DC. Perhaps designer do not know what is difference between 50ohm resistance and 50 ohm impedance in case that we handle any other than DC - ELF - VLF.
Most designs implement a switchable 50 ohm feedthrough termination in front of the high impedance buffer which adds significant input capacitance compromising the 50 ohm input impedance. At 200 MHz and below this is not a problem but above that it can be; my 300 MHz 2440 handles it well enough. Some oscilloscopes route the input signal around the high impedance buffer when in 50 ohm mode like the 350 MHz Tektronix 485 and dedicated high frequency oscilloscope usually lack a high input impedance buffer.
Best modification is not rise analog bandwidth but reject it and/or modify bandwidth shape more steep like "brickwall" some amount under Nyquist wall. When samplerate drops, corner f need also drop.
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With well designed analog front end and its BW shape and then perfect made Sin(x)/x interpolation there do not exist any form of signal aliasing. As long as analog BW and its shape is ok for used samplerate and signal reconstruction using Sinc.
Except for raising the real time sample rate or using equivalent time sampling, there is no good solution for this in a time domain instrument. If the filter shape does not have linear phase, then the filter itself will effectively create the same problem which rules out filters which have higher performance in the frequency domain. The best solution I have seen is in some early Tektronix DSOs which implemented 4 pole Gaussian bandwidth filters.
Yes, all this is, in practice, quite complex and need do some compromise.
Of course there is many solutions and all these
Rising real time samplerate related to BW. (in low gfrequency scopes today quite easy)
ETS is still useful in some cases but only if quality is good
Better filters in analog front end. Too often designers forget this in low end scopes!
Doing as perfect Sinc as possible. Even most of low end scopes they try - but as seen, some not even try.
Here is examples and not for argumenting if Siglent is good or bad. Only just for example for some random readers who have total lack of knowledge about these things. (Examples made using Siglent SDS1102X+ but this is not important here)
First image:
Some rough image about BW shape. (but not for evaluate this naamed scope real BW or BW shape, only for example for this discuss)
Note that this scope is named as 100MHz.
Image is made using slow sweep from around 1MHz to 360MHz linearly and sweep time 6s. One horizontal div 30MHz
There is vertical cursors what show around -3dB level related to low freq start.
Then there is marker A. It is around 100MHz position. (model name freq)
Then there is marker B. It is around 250MHz. If this scope is used both channels on, samplerate is 500MSa/s what means that Nyquist wall is 250MHz.
We can see that even with this frequency leevel have not dropped even 6dB. All what ADC get over this frequency when 2 channels is in use produce aliasing. And this need understand that also example square wave harmonics go very easy over this if there is enough fast risetime.
Sine wave aliasing is what it is all know it.
Here is example about other form of aliasing. Corners wobbling.
Second image:
1GSa/s and not visible aliasing. Also it can see when look rise time measured statistics (look sdev)
Third image:
sample rate is lowered to 500MSa/s. (two channels in use, CH2 trace is top of image)
Now we can see high amount of aliasing. Also risetime statistics show it.
But quess what, if we take now couple of one shots we can find also waveforms what show "better risetime" . With 500MSa/s there can find single shots what have 1.9ns risetime and with 1GSa/s fastest risetime is 2.1ns. Fun, is it. If I do some "trics" using example transfer line ringing I can get really weird results. Here in these examples signal is known. Source is health Tektronix 284 pulse generator what produce around 70ps risetime without here meaningful overshoots and it have also quite flat top enough time. But, as can see in first image, analog front end filter is not ok for 500MSa/s. If analog front end have more steep filter so that 100MHz is not attenuated and -3dB is example 150MHz and then 200MHz is highly attenuated - corners wobbling (risetime variations) is away.
After then think Rigol 250MSa/s... and its wide open analog front end... and still some peoples want it even more wide BW.
When you see something you need next think is it DUT or scope what do it. Experienced people may easy regognize things quite easy (but in some cases it also need extra thinking and time more or less)
Of course analog scopes are naaturally totally free from these aliasing things what ever channels are in use and what ever horizontal speed. (this is why I still use analog scope in some repair/service situations wwith really unknown signals. I need make money, not spend my time for fun)
This image is NOT VALID for evaluate this used oscilloscope real BW or its shape. This is because sweep generator level accuracy (flatness) is not checked with sufficient reliability. But this image can use for this subject in this message.
Fast edge from TEK 284. Scope 1GSa/s and Sin(x)/x ON
No visible aliasing.
Fast edge from TEK 284. Scope 500MSa/s and Sin(x)/x ON
Strong visisible aliasing. Because there is frequency components over Nyquist limit what are not enough reduced before ADC
(look BW shape image.)