** File: TPSht_03.hlp
** Index: 42

** More Sheet View Help
   :: Filtering commands
   :: Smoothing commands


Û  Filtering

    This menu contains commands that
perform digital filtering.  These filters
are infinite impulse response (IIR)
filters.

Û  Low-Pass

    This command lets you perform low-pass
  digital filtering.  It displays the
  Low-Pass Filter dialog box.  In this
  dialog box, you specify the cut-off
  frequency F0.  This filter only lets
  signal components with frequency less
  than F0 pass through.

Û  Hi-Pass

    This command lets you perform high-pass
  digital filtering.  It displays the
  High-Pass Filter dialog box.  In this
  dialog box, you specify the cut-off
  frequency F0.  This filter only lets
  signal components with frequency greater
  than F0 pass through.

Û  Band-Pass

    This command lets you perform band-pass
  digital filtering.  It displays the
  Band-Pass Filter dialog box.  In this
  dialog box, you specify the lower cut-off
  frequency F0 and upper cut-off frequency
  F1.  This filter only lets signal
  components with frequency between F0 and
  F1 pass through.

Û  Notch

    This command lets you perform Notch
  digital filtering.  It displays the
  Notch Filter dialog box.  In this dialog
  box, you specify the fiducial frequency
  F0 and the notch width e0.  This filter
  removes only a narrow frequency band
  around the fiducial frequency F0 with
  bandwidth 2*e0.


Û  Smoothing

    This menu contains commands that
perform digital data smoothing.  For
engineers and scientists, experimental
data often contain a large amount of
spurious noise.   TechPlot implements
several commonly used smoothing techniques
for the purpose of removing noise from
observed data.  Each of the commands in
this menu will display a dialog box.  You
will need to specify the column you want
to smooth and window sizes (if any) in the
dialog box.

Û  Lanczos

    This method is due to Lanczos; it is a
  fourth order smoothing of data points.

Û  Averaging

    This is the simplest type of filter; it
  is also called the linear filter.
    The following moving window methods
  (left and right) are special cases of
  this method.  You specify both left and
  right window sizes in the dialog box. 

Û  Moving Window (Left)

    This method uses the same formula as
  above.  In this case, NR=0 and NL is the
  window size.  You specify the left
  window size in the dialog box.

Û  Moving Window (Right)

    This method uses the same formula as
  above.  In this case, NL=0 and NR is the
  window size.  You specify the right
  window size in the dialog box.

Û  Savitzky-Golay

    This smoothing routine is adapted from
  Press et al [13]; it consists of fitting
  a least squares fourth degree polynomial
  through the data point and several points
  on either side.  The data point is
  replaced by the value of the fitted
  polynomial evaluated at the abscissa of
  the data point.  The left and right
  window size is specified by user in the
  dialog box.

Û  Gram 1-3

    This method uses Gram's first-degree
  three-point formulas, as described in
  Hildebrand's "Introduction to Numerical
  Analysis", Chapter 7, to smooth a series
  of equally spaced values.

Û  Gram 3-5

    This method is similar to Gram 1-3,
  except that Gram's third-degree
  five-point formulas are used.
