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== filter traces ==

'''command''': FILTER <kind> <trc-list> [<lo-wdw> <hi-wdw>] [<att>]

Filters traces with filters read in previously by a FILI command (kinds 'F' and 'R') ar attenuates traces (kind 'A'). All filters of the specified kind (<kind>) in memory are applied sequentially to the traces. If no time window (<lo-wdw>, <hi-wdw>) is specified, the whole traces are filtered. If <kind> 'A' is selected, the desired attenuation must be passed in parameter <att> (t* in sec).

The result of filtering is displayed in new traces. The input traces remain unchanged.

=== parameters ===

 * <kind> ''parameter type: char''[[BR]]
   Kind of filter.  Valid values are
   * 'F' - applies FFT filter, previously read in by a "[ShFili FILI] F <file>" command
   * 'T' - applies digital filter, previously read in by a "[ShFili FILI] T <file>" command
   * 'R' - applies recursive filter, previously read in by a "[ShFili FILI] R <file>" command
   * 'A' - attenuation with t* = <att> sec
   * 'H' - computes Hilbert transformation
   * 'M' - computes minimum delay wavelet
   * 'P' - (undocumented)

 * <trc-list> ''parameter type: trace list''[[BR]]
   Input traces for filtering. These trace remain unchanged. If no time window is entered, all traces are filtered.

 * <lo-wdw>, <hi-wdw> ''parameter type: real''[[BR]]
   Time window on all traces. The filtering of the input traces is restricted to this time window.

 * <att> ''parameter type: real''[[BR]]
   Attenuation (t* in sec). Only valid for <kind> = 'A'.

=== qualifiers ===

 * /taper=<tapval>[[BR]]
   Valid only for FFT and digital filters. Applies a cosine taper to filtered trace in frequency domain. <tapval> ranges from 0.0 to 1.0. Default value is 1.0. The taper is started at sample <tapval>*N if N is the length of the trace in frequency domain. A value of 1.0 and greater means that no taper is applied.

 * /demean[[BR]]
   (undocumented)

 * /lpc[[BR]]
   (undocumented)

=== example ===

 `filter F ALL`::
 filters all traces with the previous read filter in full length

 `filter F 1-3 10 110`::
 filters traces 1-3 within time window 10..110