Re: [Discuss-gnuradio] FFT scaling consistency

[Martin Braun]

On 11/26/2014 12:07 PM, Sylvain Munaut wrote:
> 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.

The peak loss is a function of the window length and its type. You can
calculate the value by:

loss = 1/(N * l2_norm(w)) * |\sum_{n=0}^{N-1} w(n)|^2

...hope my pseudo-latex makes sense :)

For a blackman-harris window, it's very close to 3 dB for most window
lengths. For complex, you're applying it twice, though, hence the
difference.

>  - I certainly don't see why Wx or Qt would make a difference

That must be a bug or something. Looks like the WX results are closer to
the truth.

M