Re: [Discuss-gnuradio] FFT scaling consistency

[Marcus Müller]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Hi,

at least Window scaling differing between QT and WX is in fact a bit
irritating...

Cheers :)

Marcus

On 11/26/2014 12:07 PM, Sylvain Munaut wrote:
> Hi,
> 
>> Then: no, QT GUI does that, see [1] (generated by [2]). The tone
>> at samp_rate / fft_length * 10 has a power of 0 dB; also,
>> Gaussian noise with an amplitude of 1 has an average (picture is
>> heavily averaged) power of -20 dB == 1/fft_length. Perfect!
> 
> Oh, that's interesting.
> 
> I didn't see that when I did the test here. Turns out it's the
> window selection, if you select Rectangular, you have 0dB and it's
> consistent between WX and Qt.
> 
> If you select something else, then it's no longer 0dB and it
> becomes inconsistent between the WX and Qt widgets. Now obviously
> windowing will have some effect on the peak value, but: - I didn't
> expect it to be this large, I expected more like a few tenth of dB,
> not precisely 3 or 6dB. - I certainly don't see why Wx or Qt would
> make a difference
> 
> 
>> To the complex vs. real discussion: Picture [3] tells me that I
>> see the noise at -23 dB; now, this will get extremely
>> philosophical whether when observing a real signal this should be
>> -20 dB instead.
> 
> Yes, it's definitely more of a philosophical question than anything
> else. Honestly I don't really care either way, I just though I'd
> bring this up at the same time and see if there was a "convention"
> that was expected.
> 
> Cheers,
> 
> Sylvain
> 
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1

iQEcBAEBAgAGBQJUdbtlAAoJEAFxB7BbsDrLzggH/0AwVlFLkoGBdmwqRrrQkW17
YDoXMpk/RMKRwYECoXYw/mr4tDk2OqwwM2I9IfLQwb/tWc7YF5ocXipbtJMdb4tL
yiaISddiEyspcT/7KAwNeRYXU61dFPCJBkp9+2TI/kGoH6qIDM4+fW5C3dkQqeaa
SdVQMWySWNAmtYBoyxOyGem7UWamNOPw9cVCpcGV3xbmjw/IJGm9DZgHLJ5fwSUA
Epzy+D+XGflfPQlpFoeuGw7zo21/PN6BP+OxFaL7eFk1YYgiYcXeS/kl1AENxQkE
OnGy2y7lQOqCJe7SAGArARANp1x5926yXM4aS9keUUFsGqT/uoATvUis6i/O+8c=
=TuxP
-----END PGP SIGNATURE-----