source: SH_SHM/trunk/help/FFT.HLP @ 206

command FFT <trc-list> <lo-time> <hi-time> <k> [<m>]
===========

key: FFT power spectrum

Computes power spectrum of input traces (given by <trc-list>)
using the FFT.  For the computation only the time window
between <lo-time> and <hi-time> on the input traces is used.
<k> specifies the number of partitions on the input traces.
The resulting power spectrum is the sum of the power spectra
of the separate partitions.  <m> is the length of a partition
in samples.  <m> must be a power of 2.  If not specified it
is determined automatically as large as possible.

parameters

<trc-list>  ---  parameter type: trace list
   List of traces to compute power spectum.

<lo-time>, <hi-time>  ---  parameter type: real
   Time window on input traces (sec.).  If not entered the
   current display window is used.

<k>  ---  parameter type: integer
   Number of partintions on each trace

<m>  ---  parameter type: integer
   Length of each partition in samples.  Must be a power of 2.
   If not entered it is determined automatically as large as possible.


qualifiers

/OVERLAP
   If specified the partitions overlap by 50%.


Examples:

   FFT/OVERLAP 1-3 0. 50. 3
      ! computes power spectrum of traces 1-3 within a time window
      ! from 0. to 50. sec.  Number of partitions is three.  The
      ! partitions are overlapping.   <m> is determined automatically.

   FFT 1;;;3 512
      ! computes power spectrum of trace 1 within the current display
      ! window.