### filter

Applies a Butterworth filter to the seismograms. The filterType can be CAUSAL or NONCAUSAL or TWOPASS, with the last two being equivalent and NONCAUSAL being the default. The default number of poles is 2. This is a relatively simple implementation and so is a memory and cpu hog. You are highly encouraged to use the much nicer oregonDSPFilter instead.

### Example

    <filter>
      <lowFreqCorner>
          <value>50</value>
          <unit>SECOND</unit>
      </lowFreqCorner>
      <highFreqCorner>
          <value>5</value>
          <unit>HERTZ</unit>
      </highFreqCorner>
    </filter>

### This consists of

<filter>

<lowFreqCorner>
cornerSetting
</lowFreqCorner>
<highFreqCorner>
cornerSetting
</highFreqCorner>
<numPoles>integer</numPoles> optional
<filterType> optional
choice
NONCAUSAL
CAUSAL
TWOPASS
</filterType>
</filter>

### Places this can be found

In seismogramProcess there is a choice between all of the following

- printlineSeismogramProcess
- sacWriter
- mseedWriter
- asciiWriter
- wavWriter
- recordSectionDisplayGenerator
- responseGain
- phaseCut
- requestCut
- merge
- gapFill
- rMean
- rTrend
- taper
- externalWaveformProcess
- seismogramScript
- localSeismogramTemplateGenerator
- filter
- rms
- oregonDSPFilter
- forkProcess
- alwaysSuccess
- phaseSignalToNoise
- compoundPhaseSignalToNoise
- seismogramImageProcess
- legacyExecute
- seismogramAND
- seismogramOR
- seismogramNOT
- someDataCoverage
- noDataGaps
- fullDataCoverage
- integrate
- differentiate
- transferResponse
- collapseOverlaps
- div
- mul
- invertFlippedChannels
- seismogramSampling
- decimate
- stddev
- rms
- mean
- minMax
- compressionType
- availableDataPlus