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Test Equipment / Re: Choosing between entry-level 12-bit DSOs
« Last post by Mechatrommer on Today at 06:11:55 pm »i just copied lanczos resampler code lying around in the internet somewhere, i dont have skill to code real Sinc filter nor i know how lanczos resampler is coded/works, assume its a black box functions. and yes i feed it with sampled points visible on screen and it returned like 10X points (sampled + interpolated points) and then plot on screen. i can guarantee those curve will pass through real sampled points... open source code like this... https://gist.github.com/kode54/6338299i tuned my sim files to this setup, 220MHz sampled at 500MSps (f = Sr / 2.27), here is what i come up with. so it seems Rigol and VisaDSO got broken implementation.That interpolation looks broken indeed. It seems to assume that the sampled data points are alway the extrema of the curve. Why would that be the case? Whatever that "smooth" interpolation is, it's not sin(x)/x, I would say.
Edit: Did you ask for a sin(x)/x interpolation through all the linearly interpolated datapoints, by any chance? That might explain the strange results. Of course only the actual sampled points must be fed to the interpolation.