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| Sub: Rigol's DHO800 Oscilloscope (Gibbs Effect & Aliasing Misunderstanding) |
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| wasedadoc:
--- Quote from: Mechatrommer on October 29, 2023, 02:11:35 pm ---mind to tell what filter is that? or if that feasible to put on DSO front end? --- End quote --- Photo shows filter output when sine wave input frequency repeatedly swept linearly from 100kHz to 3MHz. (That range does not occupy entire screen width. It should be obvious where the two frequency extremes are.) |
| wasedadoc:
--- Quote from: nctnico on October 29, 2023, 03:56:03 pm ---If you are low-pass filtering, you are removing higher harmonics. The ringing on a bandwidth limited square wave are not Gibbs ears. Just less harmonics. Because Gibbs ears are a digital signal processing artefacts from using sin x /x reconstruction, you can't get these on an analog scope because the whole digital signal processing step isn't there. --- End quote --- If the ears are as you claim "a digital signal processing artefacts from using sin x /x reconstruction" please explain why they are only present on one trace. |
| Mechatrommer:
--- Quote from: wasedadoc on October 29, 2023, 04:57:22 pm --- --- Quote from: nctnico on October 29, 2023, 03:56:03 pm ---If you are low-pass filtering, you are removing higher harmonics. The ringing on a bandwidth limited square wave are not Gibbs ears. Just less harmonics. Because Gibbs ears are a digital signal processing artefacts from using sin x /x reconstruction, you can't get these on an analog scope because the whole digital signal processing step isn't there. --- End quote --- If the ears are as you claim "a digital signal processing artefacts from using sin x /x reconstruction" please explain why they are only present on one trace. --- End quote --- you misunderstand him... to him the real signal that you captured is not Gibbs, since Gibbs only is the one calculated out of Sinc interpolator. however similar they look like. you do know what a pedantic and literalist are right? there is no point continue arguing round and round. i'm afraid 2N3055 will miss my challenge posts earlier.. |
| ebastler:
--- Quote from: Mechatrommer on October 29, 2023, 05:16:33 pm ---to him the real signal that you captured is not Gibbs, since Gibbs only is the one calculated out of Sinc interpolator. however similar they look like. you do know what a pedantic and literalist are right? there is no point continue arguing round and round. --- End quote --- Yes, that seems to be the problem. We just get circular arguments here: "No, what you show is not Gibbs, since according to my definition it is not Gibbs, but I won't tell you my definition." I feel strongly reminded of the "Is digital always binary?" thread in the Beginners section, with nctnico playing the radiolistener part. And I think I should draw the same conclusion as in that other thread and stay out of this. |
| nctnico:
--- Quote from: ebastler on October 29, 2023, 05:55:38 pm --- --- Quote from: Mechatrommer on October 29, 2023, 05:16:33 pm ---to him the real signal that you captured is not Gibbs, since Gibbs only is the one calculated out of Sinc interpolator. however similar they look like. you do know what a pedantic and literalist are right? there is no point continue arguing round and round. --- End quote --- Yes, that seems to be the problem. We just get circular arguments here: "No, what you show is not Gibbs, since according to my definition it is not Gibbs, but I won't tell you my definition." --- End quote --- There is no 'my' or 'others' definition. Again, the Wikipedia article is super clear on this! You simply can't create a perfect square wave using fourier series. Not even with an infinite number of harmonics. This page shows the effect of sin x/x and the Gibbs ears related to the Nyquist limit very clear: https://www.embedded.com/filling-in-the-blanks-in-digital-oscilloscope-waveforms/ https://www.embedded.com/filling-in-the-blanks-in-digital-oscilloscope-waveforms/ |
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