Signal Processor Design and Additional Noise Models - Measurement While Drilling Signal Analysis, Optimization and Design - page 174

6.7 Low Pass Butterworth, Low Pass FFT and Notch Filters
The capabilities shown in this final section are standard and available with
numerous software tools. We provide typical results without further comment.
Figure 6.7a. Low-pass Butterworth filter.
Figure 6.7b. Low-pass FFT filter.
Figure 6.7c. Notch filter.
Software reference. Fortran source code is available for the five filters in
Sections 6 and 7 in C:\MWD-06 under obvious filenames. These, together with
the algorithm codes in Chapters 2-5, provide the basic tools for high-data-rate
signal processor testing and design. It goes without saying, of course, that field
data is all-important, and should be collected with a “wave orientation.” In
other words, careful attention should be paid to bottomhole assembly details,
borehole annular geometry, drillbit type, surface setup and mud sound speed,
noting that the latter may vary along the drillstring as pressure and temperature
conditions change.