I see. I don't feel quite so stupid for having not found it myself, now! On Mon, 10 Aug 2015 at 13:37 Marcus Müller <[email protected]> wrote:
> Hi Tom, > > added the block, opened the block properties, had a look at the id; I knew > that these kind of blocks live within gr-filter, so > > cd gr-filter > vim grc/*rational*.grc ##that's where the block definitions for GRC reside > > found out that the non-base variant used rational_resampler_$(type), but I > had a look into filter, and only found rational_resampler_base_*; so I > guessed it was a python file. > Went into python/filter, and opened rational_resampler.py, based on it > being the only python file that was possibly relevant here. > > You know, that's really unintuitive, and I think we'll need some helpers > or better documentation that makes finding such things easier. > > Best regards, > Marcus > > > On 10.08.2015 14:31, Tom Cook wrote: > > On Mon, 10 Aug 2015 at 13:14 Marcus Müller <[email protected]> > wrote: > >> Hi Tom, >> >> I just had to look this up. If you're in GRC, you have "rationale >> resampler" and "rational resampler base"; they do basically the same, but >> if you use the one without "base", and don't specify the taps, GNU Radio >> just automatically designs a filter that avoids all aliasing and imaging, >> which is done with a python wrapper around the C++ >> rational_resampler_base_xxx's make function[1]. That's pretty handy in most >> use cases, but not too much if you want your own filter for some reason. >> >> If you're using the "base" variant, you *must* specify the taps >> yourself, because you directly invoke the C++ block's maker. If you go >> ahead and just use "[1.0]" as taps, you get the aliased results from my >> pictures. >> >> So if you happen to *want *to specify the taps, because you can >> integrate the functionality of a downstream filter into the resampler to >> save CPU cycles, it doesn't make a difference which block you use. >> > > Ah, I see. Many thanks for taking the time to explain this. Where did > you look to find out that 'rational resampler' block does an automatic > filter design for you? > > Regards, > Tom > > >
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