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Manpage of FFTFILTER Content-type: text/html

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

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.

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Time: 21:00:09 GMT, November 03, 2010