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FFTFILTER
Section: Misc. Reference Manual Pages (1L)
Updated: 16 April 1999
Index
Return to Main Contents
NAME
fftfilter - compute complex fft on input (ao).
SYNOPSIS
fftfilter
[
-r
]
[
-d
transformDirection
]
[
-n
lengthTransform
]
[
-z
zeroFillFromdatapoints.
]
DESCRIPTION
fftfilter
performs a complex fourier transform on its input data.
The input is taken from the standard input and should be real*4
floating point format. The real value of each complex number should be
followed by its
imaginary part.
The length of the transform is determined by the
-n
option. If the
-z
option is specified then datapoints points will be used with zero
extension out to lengthTransform.
The filter continues performing ffts until there is no more input data.
Any data at the end that does not fill up a complete transform length
will
be ignored (unless
-z
is used then the last points will be zerofilled).
The output data is real*4 floating point format and is written to
standard output.
The output data order is DC (real, imaginary), lowest to highest
positive frequencies,
and then highest to lowest negative frequencies.
OPTIONS
- -d direction
- Direction of the transform.
It can be f for a forward transform (positive exponent)
or r for a reverse transform (negative exponent). The default direction
is f. Reverse transforms are scaled by
1/lenghtTransform.
- -n length
- The complex length of the transform to perform.
The default value is 1024.
- -r
- Remove dc before transforming.
- -z datapoints
- Read datapoints complex points and then zero extend to length.
Any points at the end will also be zero extended.
EXAMPLES
Input an ri data tape, unpack, convert to real*4 and then do
a number of 2048 length reverse transforms.
- dd if=/dev/nrst12 bs=64k|stripVme -h|unpriVtoi4|\
i4tor4|fftfilter -d r -n 2048 > fft.out
FILES
~phil/util/filters/fftfilter.c location of source code
SEE ALSO
stripVme(1L)
unpriVtoi4(1L)
i4tor4(1L)
DIAGNOSTICS
The length of the transform will be limited by how much memory the
program can allocate to hold the transform data. The routine is not
limited to powers of 2 length.
Index
- NAME
- SYNOPSIS
- DESCRIPTION
- OPTIONS
- EXAMPLES
- FILES
- SEE ALSO
- DIAGNOSTICS
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Time: 21:00:09 GMT, November 03, 2010