Changes between Version 1 and Version 2 of decimate


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Timestamp:
03/25/12 16:13:51 (8 years ago)
Author:
branden
Comment:

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  • decimate

    v1 v2  
    88 
    99== Details == 
    10 The Decimate module implements multi-stage filter and decimation routines to process wave data (TYPE_TRACEBUF2) coming from the InRing defined in decimate.d. Decimated trace messages are written to the OutRing with their SCNs changed as specified in decimate.d. The decimated trace message retains its TYPE_TRACEBUF2 type, but it (normally) has a new SCNL name. 
     10The Decimate module implements multi-stage filter and decimation routines to process wave data (TYPE_TRACEBUF2) coming from the !InRing defined in decimate.d. Decimated trace messages are written to the !OutRing with their SCNs changed as specified in decimate.d. The decimated trace message retains its TYPE_TRACEBUF2 type, but it (normally) has a new SCNL name. 
    1111 
    1212Decimate uses FIR filters to reduce the incoming wave frequency content down to the Nyquist frequency of the output wave. FIR filters have the advantage of being strictly causal and stable. However, there is considerable delay introduced by a FIR filter. Fortunately FIR filters have linear phase so the delay does not change the shape of the wave. The delay will be removed from the data by adjusting their timestamps. This adjustment makes the filter acausal: small precursory artifacts will be seen in front of impulsive wave arrivals. This is an inherent characteristic of FIR filters. See "Of Poles and Zeros" by Frank Scherbaum for a method of removing these artifacts.