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

[Jens Elsner]

> > From: Marcus D. Leech <address@hidden>
> >
> > Let's say I have an FFT output that's  many, many, bins wide, and I want
> > to compress that information into a narrower display (let's say from 4M > 
> > bins down to 1024 bins).
> > 
> > My approach has been to sum up each set of [4M/1024] bins, and use that
> > as the final output. 
> > 
> > Marcus Leech
> 
> I think adding FFT bins is the correct way. But, for me I always select the 
> maximum in these bins. I'm not sure that this is right but it gives me a good 
> look over my spectrum data.

Spectrum Estimation is not trivial - I highly recommend having a look at
"Introduction to Spectral Analysis" by Stoica and Moses. A mathematical
yet readable introduction.

To solve you problem in a mathematically way, you can use windowing 
in the time domain with subsequent overlapping block averaging 
(Welch's method).

Gives a good practical estimate. Code for GNU Radio is here:

https://www.cgran.org/wiki/SpecEst

Integrating the FFT bins is just fine, but you probably loose frequency
resolution that way (if that doesn't matter, just leave it).

Best regards,
Jens