NAME

     tvdafd  - do true amplitude time varying frequency equaliza-
     tion

SYNOPSIS

     tvdafd [ -Nntap ] [ -Ootap ] [ -Bttap  ]  [  -lwlslide  ]  [
     -ovovlp ] [ -flfl ] [ -fhfh ] [ -nsns ] [ -nene ] [ -rsirs ]
     [ -reire ] [ -M ] [ -V ] [ -? ]

DESCRIPTION

     tvdafd performs time varying true amplitude spectral balanc-
     ing by computing frequency boost functions [ f ** exponent ]
     and applying them to the amplitude spectra over a series  of
     sliding  windows in time. The boost functions are given in a
     flat file of time vs power exponent. As the  sliding  window
     moves  down  the trace is fourier transformed, the amplitude
     spectrum powered by the appropriate boost function, and  the
     inverse  transformed  data  put  back  into the final output
     trace.  The final time output is the post-filtered  to  roll
     the ends of the boost function.

     The response of  this  type  of  frequency  equalization  is
     excellent compared with standard equalizers (see e.g. dctvf)
     based on gain correcting narrow passbands.  Side  lobes  are
     usually  much  lower,  and  of course the correction is true
     amplitude.

     tvdafd gets processing controls from the command line.  Rea-
     sonable defaults are set up.


  Command line arguments
     -N ntap
          Enter the full path of the  file  containing  the  data
          set.  Default is a pipe in.

     -O otap
          Enter the output file name  for  the  filtered  traces.
          Default is a pipe out.

     -B ttap
          Enter the input file name for the  time-boost  exponent
          [f  **  exponent] functions. Each line of the file con-
          sists of a time and a power exponent separated by white
          space  as  control  points.  These  control  points are
          interpolated smoothly over  the  trace  length  of  the
          input  data  so  that there is an interpolated exponent
          for each sliding window position. As the sliding window
          moves down the trace is fourier transformed, the ampli-
          tude spectrum powered by the  appropriate  boost  func-
          tion,  and  the  inverse transformed data put back into
          the final output trace. Values of the exponent close to
          zero  will  result  in little change to the output fre-
          quency distribution; exponents of 1 or 2 will generally
          result in fairly substantial changes.

     -lw lslide
          (integer)  Enter  the  length  in  ms  of  the  sliding
          analysis/application  window.  This  (and  ovlp  below)
          govern how rapidly the the boost function  can  change.
          Default = 500ms

     -ov ovlp
          (integer) Enter  the  overlap  in  ms  of  the  sliding
          analysis/application window. Default is 1/2 lslide.

     -fl fl
          (float) Enter the  low  cut  frequency  in  Hz  applied
          post-dafd to prevent spectral end effects. Default = 5

     -fh fh
          (float) Enter the high  cut  frequency  in  Hz  applied
          post-dafd  to  prevent  spectral end effects. Default =
          .75 Nyquist.

     -ns ns
          (integer) First trace in record to process  (default  =
          1).  Traces prior to this in each record will be passed
          unprocessed.

     -ne ne
          (integer) Last trace in record to  process  (default  =
          all).  Traces  after this in each record will be passed
          unprocessed.

     -rs irs
          (integer)  First  record  to  process  (default  =  1).
          Records prior to this will be passed unprocessed.

     -re ire
          (integer) Last  record  to  process  (default  =  all).
          Records after this will be passed unprocessed.

     -M   If present do not restore early on mute.

     -V   If present give verbose printout

     -?   Query  mode.   With  this  flag,  tvdafd  will  give  a
          description  of the command line arguments and stop the
          program.

DISCUSSION

     Applying a power function [ f ** exponent ]  to  the  ampli-
     tude  spectra  can result in noisy output if the exponent is
     too large for the S/N characteristics of the input  data.  A
     portion  of  data  should be used to determine the limits of
     the exponents.

BUGS

     Beware of applying an overly ambitious boost  function;  the
     result is usually a very noisy output data set.

See Also

     dafd  for  non-time  varying  version  and  also  dctvf  for
     ormsby-based non-time varying version.

AUTHORS

     P. R. Gutowski, Amoco Production Technology Center, 1996

COPYRIGHT

     copyright 2001, Amoco Production Company
               All Rights Reserved
          an affiliate of BP America Inc.