Re: [Discuss-gnuradio] The power of N log N

[Matt Ettus]

Lamar Owen wrote:

> Yeah, been tracking CVS on a machine here, and noticed a load of differences. 
>  
> One quick question: now that tweak_adc_offset is no longer in the repository, 
> is the ADC DC offset automatic?  I still see a DC spike in the FFT output.


> In the large FFT case, I notice that the resulting trace is significantly 
> thicker, and it doesn't seem to average out.  I'll have to look, but an 
> 'fft_smoothing' argument (to thin the trace) would be what I'd need to get 
> the resolution I need.

What you are seeing is that ALL points end up being plotted.  If you
assume you have a horizontal screen resolution of 1024 point, but are
plotting a 128 K-point FFT, you end up with 128 points being plotted in
every X position.  Each of those points is likely to be slightly
different in amplitude, so you see a thick line.  Some sort of "video
averaging", to borrow a term from spectrum analyzers, would be necessary
to clean that up.

Matt