Re: Resampling radio data

[Marcus Müller]

Oh, sorry, didn't mean to imply that! FFT interpolation might work well (if you 
can live
with the sinc sidelobes).

I do have a question, though: Why do you go for a 4600-FFT? why not simply a 23 
FFT?

Best regards,
Marcus

On 17.02.21 15:56, Brian Padalino wrote:
> On Wed, Feb 17, 2021 at 8:01 AM Marcus Müller <mueller@kit.edu 
> <mailto:mueller@kit.edu>>
> wrote:
> 
>     Rough performance estimate:
> 
>     for a 1/10 transition width filter (which is sufficient to keep 20 of 25 
> MHz Nyquist), you
>     need an expertly guesstimated [1] 24-ish taps, so go for 25 taps: that 
> happens to be
>     exactly the minimum filter length that we can use in an 25-interpolating 
> rational
>     resampler and still do the full polyphase decomposition trick to run the 
> filter at the
>     least rate of the system.
> 
>     For "1 tap per branch", I have a rough 60 MS/s for *my PC* in mind. So, 
> My guess is that
>     it will work for 46->50 MS/s, not for 92->100 MS/s, on *my PC*.
> 
>     Problem: this is an inherently badly multi-threadable workload, unless 
> I'm overlooking
>     something. So, having 48 cores isn't better than having 2.
> 
> 
> Just curious, why do you think the FFT interpolation won't work?
> 
> So long as the block sizes are appropriately picked (how about we stick with 
> 4600 input
> size, and 5000 output size), the frequency components should all line up and 
> be phase
> aligned from block to block.  There might be a little scaling factor that the 
> resulting
> samples will be off due to the difference in FFT length, but otherwise I 
> think it should work.
> 
> Moreover, the FFT work can be done in parallel and utilize all the cores.
> 
> I did a quick little test and I think it should work.  Yes?
> 
> Brian

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