C'mon Fungus, we had lengthy discussions (plural) about that first Rigol video and Hires mode in general.
First, that first video from Rigol is wrong and misleading. They abused fact that Rigol MSO5000 has better overdrive recovery than RTB2000 (which is a shame they didn't point that out because it is very important parameter), but choose to fake less noise by using that. Also it is pointless anyways, because despite better recovery it still distorts signal so it is not to be trusted anyways.
I didn't post if because of that. I posted it because there's a clear moment where hires mode is turned on and yu see the difference. The color mode is also interesting/useful and it's shown clearly.
As for Hires, it IS NOT replacement, fix, or solution for high noise in input channel of the scope.
I specifically said that it wasn't, but it does help.
Hires uses filter that filters high frequencies out. That way it filters out noise energy in those high frequencies, leaving just low frequency noise. Which makes residual noise smaller and only fraction of full range noise. It does that by using Hires to make a 350 MHz scope a 50Mhz or 20Mhz or 500kHz scope, depending on how much bits of Hires you apply.
Huh? If you're sampling at 8GHz then you have multiple samples within each 350MHz time period. Averaging them won't make the bandwidth less then 350Mhz, it simply reduces the noise inherent in the ADC process.
Hires is not averaging. Averaging is useful only for repetitive, low phase noise (low jitter) signals.
Hires is lowpass filtering.
Single channel calculations (for 2 ch divide by2, for 3 and 4 channels divide by 4)
For 1 bit improvement BW is 0,238 (1/4) of original Nyquist (8GS sample rate, 4GHz Nyquist effective 1GHz 1 h/250MHz 4ch).
For 2 bit improvement BW is 0,0625 (1/16) of original Nyquist (8GS sample rate, 4GHz Nyquist effective 250MHz 1ch/62.5MHz 4ch).
2 bit improvement is roughly what MSO5000 need to show similar RMS of noise to RTB2000 or SDS2000X+.
For 3 bit improvement BW is 0,0625 (1/64) of original Nyquist (8GS sample rate, 4GHz Nyquist effective 15.625MHz 1ch/3,9MHz 4ch).
So you could say that 1 bit improvement would be transparent , like you say. But not more, and since it has much more noise to begin with, it is not enough.
In practical terms, you DO NOT filter signal unless you want to do that deliberately because you only want to look at partial signal. Or shall I say, I was always missing MORE bandwidth not less.
Or I could just say your are right. It doesn't matter, and we should all just stop using any scopes with more than 20 MHz BW because it is all just some unwanted interference we don't care about anyways.
And I'm fine with your characterisation that if run lowpass filtered it is a fine normal noise scope. Except Rigol should be selling it as a 50 or 20 MHz scope because that how it's going to get used.
MSO5000 is good scope for the price. It has a noisy front end, but has many features that make it useful instrument. That is
despite the fact that is a bit noisy, not because noise is irrelevant. It is not unusable, but its noise figures are not good. If that is important for user, then it is.
Like I said.
I know you are trying to simplify it for a beginner, but you can't. One of the biggest problems of the beginners is not lack of answers but a lack of good questions. They simply cannot formulate their needs because they don't have enough data and knowledge.
That is why, for beginners, I tend to recommend some of the simpler, cheaper scopes. Today's entry level scopes like the SDS1104X-E or equivalents can carry a beginner for many years. Heck, they can do for a professional for most routine tasks... After many years, if they keep the hobby, they will know where to go from there... They are also easier to learn how to use, where we see that even professionals coming from CRT analog scopes need quite some time to learn how to use digital scope to its full extent.
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