SUMMARY
Flattens the spectrum of the input time series.
SYNTAX
WHITEN {N} {FILTERDESIGN|FD}
INPUT
N: The order (number of poles). The higher this number, the flatter the resultent data. High orders can clean the data up better, but they can clean the data up too much, and important data can be lost if the order is set too high. The default is 6.
FD: Performs something akin to the filterdesign command. Using the whitening coefficients, it designs the whitening filter. Output is written to disc as a set of three output files per input file. Output files have the following suffixes:
.imp: impulse response .spec: spectral responses (amplitude and phase), and .gd = group delay. Note that while the group delay claims to be a time series file, it is really a frequency series.
DEFAULT VALUES
WHITEN 6
DESCRIPTION
Add white noise to the data. Flattens the spectrum of the input time series. When this is performed prior to the spectral commands (like those in SPE, or transfer or spectrogram), it reduces the dynamic range of the spectral values, and improves the accuracy of the overall operation at high frequencies for seismic data.
Note WHITEN can be called from within the SPE subprocess, or from SAC's main shell. The WHITEN in SPE maintains the order separately from the WHITEN in the main shell. From the main shell, you can call WHITEN 4. Future calls to WHITEN from the main shell will have an order of 4, but calls to WHITEN in SPE will still have order of 6, unless it is changed at the commandline in SPE. Furthermore, the order in SPE is the same as the order related to the PREWHITEN option in SPE's COR command (setting one sets the other). Also the order in the main shell's WHITEN command is the same as the order in the TRANSFER command's PREWHITEN option.