FFT Spectral smoothing

GNU Radio
1

Hi,

i’d like to do spectral smoothing on an FFT in real time through
GNU_RADIO.

Is there a function that will allow me to do this in the GNU_RADIO
modules?

If not has anyone attempted it before, or have any suggestions as to how
I should go about implementing it myself.

Perhaps any ideas of cascading blocks that do exit.

Thanks,

Aadil

2

2007/6/21, Aadil V. [email protected]:

Perhaps any ideas of cascading blocks that do exit.

Thanks,

Aadil

From what I can find, “spectral smoothing” is not an unambiguous term.
Could you please elaborate the problem, preferably the mathematical
definition of what you are trying to accomplish.

Best regards,

Trond D.

3

Aadil V. wrote:

i’d like to do spectral smoothing on an FFT in real time through
GNU_RADIO.

Is there a function that will allow me to do this in the GNU_RADIO
modules?

Are you referring to smoothing FFT bins over time or over frequency?

–
Johnathan C.
Corgan Enterprises LLC
http://corganenterprises.com

4

Peter M. wrote:

I guess he means time. This would greatly improve
the FFT demos, since currently there is no “video
filtering”, as the spectrum analyzer folks say.

In the current FFT demo, it is possible to right-click on the display
and select ‘Average’. This will perform low-pass filtering on each FFT
bin such that the “noise” averages to its rms value but the signal peaks
remain. This is done in the flow graph by using a
gr.single_pole_iir_filter as an exponential averager. You can do this
in the waterfall mode as well.

–
Johnathan C.
Corgan Enterprises LLC
http://corganenterprises.com

5

i’d like to do spectral smoothing on an FFT in real time through
GNU_RADIO.

Is there a function that will allow me to do this in the GNU_RADIO
modules?

Are you referring to smoothing FFT bins over time or over frequency?

I guess he means time. This would greatly improve
the FFT demos, since currently there is no “video
filtering”, as the spectrum analyzer folks say.

A more flexible spectral estimate would allow showing
nice clean noise floors at the expense of a little
measurement time.

Cheers,
Peter M.

6

On Friday 22 June 2007, Johnathan C. wrote:

Aadil V. wrote:

i’d like to do spectral smoothing on an FFT in real time through
GNU_RADIO.

Is there a function that will allow me to do this in the GNU_RADIO
modules?

Are you referring to smoothing FFT bins over time or over frequency?

General smoothing over time and frequency would be great; smoothing over
time
is doable now with averaging.

Lamar Owen
Chief Information Officer
Pisgah Astronomical Research Institute
1 PARI Drive
Rosman, NC 28772
(828)862-5554
www.pari.edu

7

Peter M. wrote:

I guess he means time. This would greatly improve
the FFT demos, since currently there is no “video
filtering”, as the spectrum analyzer folks say.

A more flexible spectral estimate would allow showing
nice clean noise floors at the expense of a little
measurement time.

If you right-click in the spectrum window you will see an option for
averaging and peak-hold.

Matt