 | | From: | attackack at yahoo.com | | Subject: | FFT phase errors | | Date: | 18 Jan 2005 10:01:32 -0800 |
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 | I've a c++ code about FFT and when i calculate the phase parameters i
see some errors. In a PDF file about FFT i've seen that:
''...this error occurs whenever the real part is negative. This problem
can be
corrected by testing the real and imaginary parts after the phase has
been
calculated. If both the real and imaginary parts are negative, subtract
180=B0
(or PI radians) from the calculated phase. If the real part is negative
and the
imaginary part is positive, add 180=B0(or PI radians). Drill this into
your mind. You have to see the phase only
extending to =B11.5708.
The smallest possible value is always chosen, keeping
the phase between -PI and PI.
It is often easier to understand the phase if it does not have these
discontinuities, even if it means that the phase extends above PI, or
below -PI.
This is called unwrapping the phase.
..=2E...........''
Now i ask...there is a code that calculate the phase correctly whit all
the different options?
P=2ES.: naturally i have real and imaginary component by FFT.
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| | From: | James Van Buskirk | | Subject: | Re: FFT phase errors | | Date: | Wed, 19 Jan 2005 02:09:39 -0700 |
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| wrote in message
news:1106071292.385110.129580@f14g2000cwb.googlegroups.com...
[snip]
Let z = x+j*y.
You want atan2(y,x).
--
write(*,*) transfer((/17.392111325966148d0,6.5794487871554595D-85, &
6.0134700243160014d-154/),(/'x'/)); end
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| | From: | glen herrmannsfeldt | | Subject: | Re: FFT phase errors | | Date: | Tue, 18 Jan 2005 10:44:17 -0800 |
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| attackack@yahoo.com wrote:
> I've a c++ code about FFT and when i calculate the phase parameters i
> see some errors. In a PDF file about FFT i've seen that:
(snip)
> Now i ask...there is a code that calculate the phase correctly whit all
> the different options?
> P.S.: naturally i have real and imaginary component by FFT.
It is called atan2() in both Fortran and C.
I believe in C++ also.
-- glen
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