On Oct 20, 3:40=A0pm, "Steve Amphlett" <Firstname.Lastn...@WhereI
Work.com> wrote:
> "Dave Brackett" <davebrack...@hotmail.com> wrote in message <gdi2ve$cu...=
@fred.mathworks.com>...
> > Hi, I have written some code to do a FFT based on this example but with=
a Hann window:
> >http://www.mathworks.com/support/technotes/1700/1702.html
>
> > I am basically doing a STFT (short time FT) and comparing frequencies a=
nd power over time. So I am splitting up a recorded signal into many segmen=
ts and computing a FFT on each.
>
> > The thing that I am finding curious though is that the more segments th=
at I split the signal into, the greater the power in the FFT for each segme=
nt. Should this be the case? I would have thought the opposite should be ob=
served because of the reduction in power that windowing causes.
>
> > Because I am using a Hann window, I have divided the FFT magnitude by 0=
.5 which is the coherent gain scaling factor.
> > I could post my code here but as it is based on the example at the abov=
e link it probably would only serve to confuse.
>
> > If someone could clarify what I should expect to see when splitting the=
signal into several segments as compared to 1 segment, with regards to the=
power, that would be useful. Thanks.
>
> Your 0.5 will correct the amplitude. =A0For energy correction, use sqrt(3=
/8). =A0Most people would express the correction the other way up:
>
> Multiply by 2 for amplitude, sqrt(8/3) for energy.
just to clarify, is the correction of energy the one to use when
plotting power?
also, I don't think the problem of the different FFT peak magnitudes
is to do with this correction factor as this just scales it by the
same amount.
cheers.
