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REVIEW - Rigol DS2072 - First Impressions of the DS2000 series from Rigol
Galaxyrise:
--- Quote from: marmad on July 12, 2013, 09:23:45 am ---ANYTIME up to 2ms/div it's not sampling at 2GSa/s, it could be - if it didn't use FIXED sample sizes.
--- End quote ---
So by that reasoning, the DS2000 already does anti-aliasing: Select the maximum memory depth and turn on anti-aliasing. But you haven't been satisfied by that "anti-aliasing" in the rest of this thread.
marmad:
--- Quote from: Galaxyrise on July 12, 2013, 03:33:07 pm ---So by that reasoning, the DS2000 already does anti-aliasing: Select the maximum memory depth and turn on anti-aliasing. But you haven't been satisfied by that "anti-aliasing" in the rest of this thread.
--- End quote ---
Sheesh... man, it seems you haven't understood the process I'm talking about at all. Selecting the maximum memory depth and turning on anti-aliasing does NOT eliminate aliases at all. Plus it's insanely slow trying to decimate 56M to display memory constantly.
This seems oddly reminiscent of trying to convince you that Rigol's High-Res mode produces the same results as everyone else.
Galaxyrise:
--- Quote ---The Rigol does NOT have to do this during sampling; it could sample at full speed (2GSa/s) into sample memory - then do random decimation (to simulate the current sampling rate) to display memory
...
ANYTIME up to 2ms/div it's not sampling at 2GSa/s, it could be - if it didn't use FIXED sample sizes. (with chart that can be recomputed with simple math.)
--- End quote ---
I translate that into:
1) Sample into sample buffer at the fastest rate memory depth + time base allows (up to 2GSa/s, ofc)
2) decimate to screen
The Rigol does that now. And we agree it doesn't fix acquisition aliasing. So that leaves me suspecting I'm missing something in your description of what you'd like the Rigol to do.
marmad:
--- Quote from: Galaxyrise on July 12, 2013, 04:36:38 pm ---
--- Quote ---The Rigol does NOT have to do this during sampling; it could sample at full speed (2GSa/s) into sample memory - then do random decimation (to simulate the current sampling rate) to display memory
--- End quote ---
I translate that into:
1) Sample into sample buffer at the fastest rate memory depth + time base allows (up to 2GSa/s, ofc)
2) decimate to screen
The Rigol does that now. And we agree it doesn't fix acquisition aliasing. So that leaves me suspecting I'm missing something in your description of what you'd like the Rigol to do.
--- End quote ---
No, the Rigol doesn't do that now.
It certainly doesn't do RANDOM decimation, and I don't think it does decimation to simulate lower sampling frequencies either.
I've written this all before:
Random decimation (stochastic sampling) is the key to anti-aliasing. Beat frequencies (aliases) are formed by regular time interval sampling.
In the image, the black crosses and dotted line show regular decimation forming an alias frequency of the true frequency. The red crosses and line show irregular (random) decimation NOT forming an alias.
Galaxyrise:
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In that picture, normally the sine wave is the true signal, and the black vs red crosses are what's written to sample memory. That produces results like on the Agilent.
My confusion is with your claim that the Rigol could theoretically anti-alias without doing the random decimation before storing samples into the waveform. If it can sample fast enough to store that sine wave into sample memory, it already doesn't alias. (If that sine wave is in sample memory, the aliased low frequency sine wave will never be what's on the screen.)
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