There's probably next to no chance this is right, but might it not have to do with the picture itself - not the waveform displayed? I mean - how do you make something out of nothing? If you don't have the sample rate necessary then you simply don't have the samples and you *will* get aliasing. Maybe there's some math-magic you can do so I guess I wouldn't rule it out, but still.
I seem to recall the idea or speculation that AA is used on the picture - ie, like in gaming - to make diagonal lines appear smoother. It's not just for gaming anymore - I believe Microsoft Office 2010 (and maybe 2007?) charts use anti-aliasing, so some people's approval and others' disgust. This could be part of what makes the Rigol displays in the newer/higher-end models look so good.
Different kind of anti-aliasing:
At slower sweep speed, the sample rate is reduced and a dedicated display algorithm is used to minimize the possibility of aliasing.
The displayed waveforms will be more susceptible to aliasing when this function is disabled.
Different kind of anti-aliasing:
At slower sweep speed, the sample rate is reduced and a dedicated display algorithm is used to minimize the possibility of aliasing.
The displayed waveforms will be more susceptible to aliasing when this function is disabled.
Ah, I see - so they themselves claim it should do something data-related, not just make the screen "pretty". And yet the benefit isn't obvious, or they haven't really implemented it yet, or it's benefit is restricted to only very specific circumstances.
I mean - how do you make something out of nothing? If you don't have the sample rate necessary then you simply don't have the samples and you *will* get aliasing. Maybe there's some math-magic you can do so I guess I wouldn't rule it out, but still.
Ah, I see - so they themselves claim it should do something data-related, not just make the screen "pretty". And yet the benefit isn't obvious, or they haven't really implemented it yet, or it's benefit is restricted to only very specific circumstances.
BTW, jneumann
I do think it's possible that Rigol might be using image anti-aliasing on some graphic items.
But in terms of waveform anti-aliasing: here's an excerpt from an Agilent document describing one technique:
Random decimation (see References)Simple decimation (= regular sampling) is the most common decimation technique in DSO’s and it is exceptionally prone to aliasing. However, the discarded samples can be used to prevent the display of aliased waveform. The random sample selection prevents an alias (or beat) frequency from developing by converting low frequency “spurs” to noise. (For masochists only ? A. V. Balakrishnan: On the Problem of Time Jitter in Sampling, IRE Trans. on Info. Theory, April 1962.)
With random decimation (= stochastic sampling) the resulting display is a fuzzy band much like what would be seen on an analog scope. However, this technique should be turned off for analysis that requires samples at exact regular time intervals.
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BTW, jneumann I do think it's possible that Rigol might be using image anti-aliasing on some graphic items.
But in terms of waveform anti-aliasing: here's an excerpt from an Agilent document describing one technique:
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Thanks Marmad - that was an interesting snippet from Agilent. Figured I'd better not use the word "impossible" haha.
Thanks Marmad - that was an interesting snippet from Agilent. Figured I'd better not use the word "impossible" haha.
No problem.
BTW, I imagine that this Random Decimation technique is what leads to the strange waveform you get when you zoom in on an under-sampled, anti-aliased waveform on the Agilent DSOs
(nicely illustrated in Janne's 'before' and 'after' images). It's a pity they removed the ability to turn off anti-aliasing (as well as interpolation) in the latest X-Series DSOs.
To DS4000 owners:
Marmad is working on a new version of my Rigol Ultravision Utilities to handle all 4 channels of the DS4000 ). Since he does not own the DSO, He'd appreciate any owners willing to be alpha/beta testers. The link for the current alpha (as well as some explanatory info)
is here.