Re: [Discuss-gnuradio] Correct method for "compressing" a power spectrum

[Marcus D. Leech]

Bob McGwier wrote:
>
> I suggest that the best algorithm for this would be the rank order
> mean alternated with the max so long as you are going to insert
> "heuristic grass".  So it would be max, ROM, max, ROM, .....
>
>
> Let [B1, B2, B3, B4, ... BN]  be powers of five adjacent bins.
>
> Put them in rank order
>
> [R1, R2, R3, R4,  ... RN]
>
> If N is even,  the rank order mean is (R_(N/2) + R_/(N/2 +1)*0.5.
> If N is odd,  the rank order mean is R_(N/2 +0.5)
>
> But I still see a problem:
>
> I suggest that in order to prevent "scalloping" of a swept tone across
> this algorithm or any other like it,  that some "bin"  in the lossy
> compression set of bins must ALWAYS be forced to take on the large of
> the power spectrum otherwise your alternative min/max/min/max might
> jump up and down as you sweep a tone through it.  Or did I miss
> something?
>
> Bob
I love that phrase, Bob.   "Heuristic grass".

I think that the real answer is to "play with it, and see what best
suits the application".   Ranking the bin might end up being
  expensive.  I'd probably use qsort(),  but I can't remember what its
computational complexity is. Just looked it up.  Worst case
  is O(N**2), and best-case is O(NlogN).   For worst-case, that's rather
brutal at 4M bins (and even worse at my maximum of
  16M bins).

This discussion has ended up being much more fascinating than I had
predicted.   Keep it up everybody!

-- 
Marcus Leech
Principal Investigator, Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org