
dfilthp(1)                   Khoros                    dfilthp(1)

PROGRAM
     dfilthp - 1D highpass frequency domain filter design

SYNTAX
     dfilthp

     -o             resulting output file (ascii polynomial file)

     [-h]           sampling frequency in hertz

     [-f1]          digital rejection frequency

     [-f2]          digital cutoff frequency

     [-tc]          gain at passband edge

     [-tr]          gain at stopband edge

     [-c]           filter class (0 = butterworth; 1 = chebychev
                    i; 2 = chebychev ii):
                    0 (butterworth),
                    1 (chebychev i),
                    or 2 (chebychev ii)
                       [default = 0]

     [-V]           Gives the version for dfilthp

     [-U]           Gives the usage for dfilthp

     [-P]           Prompts for command line options

     [-A [file1]]   Creates the answer file called dfilthp.ans or
                    file1

     [-a [file1]]   Uses dfilthp.ans or file1 as the answer file

DESCRIPTION
     ldfilthp is a high pass filter design function.  It is capa-
     ble of designing Butterworth, Chebychev I, and Chebychev II
     class filters.  A filter designed by this function will be
     an even order filter consisting of n/2 2nd order stages in a
     cascade structure, where n is the order of the filter.  The
     filter equation is output in ASCII form as a polynomial
     function of z.

     Each second order stage is of the form:

                    a + b*z^-1 + c*z^-2
             S(z) = -------------------
                    1 + d*z^-1 + e*z^-2

     where a,b, and c are the fiilter stage's numerator coeffi-
     cients, and d and e are the denominator coefficients.  The
     values of the coefficients are determined by applying a
     design algorithm based on the filter class.

     The user specifies cutoff and rejection frequencies as well
     as epsilon and lambda, two parameters that are related to
     the cutoff and rejection tolerances by:

             tc = 1/(1+epsilon^2)
             tr = 1/(1+lambda^2)

     where tc is the cutoff tolerance, and tr is the rejection
     tolerance.

     Butterworth Filters

     Butterworth filters are characterized by the property that
     the magnitude response is maximally flat in the passband.
     For an nth order filter, the first 2n-1 derivatives of the
     magnitude squared spectrum are 0 for w = 0.  A second
     characteristic is that the magnitude spectrum is monotonic
     in both the passband and the stop band.  A concavity change
     occurs at w = wc, the 3dB cutoff frequency.

     Chebychev I Filters

     Chebychev I class filters are characterized by the property
     that the magnitude response in the pass band is equiripple,
     while it is monotonic in the stop band.

     Chebychev II Filters

     Chebychev II class filters are characterized by the property
     that the magnitude response in the pass band is monotonic,
     while in the stop band it is equiripple.

REQUIRED ARGUMENTS
     -o     type: outfile
            desc: resulting output file (ascii polynomial file)

OPTIONAL ARGUMENTS
     -h     type: float
            desc: sampling frequency in hertz
            default: 1
            bounds: value > 0.0

     -f1    type: float
            desc: digital rejection frequency
            default: 0.25
            bounds: value > 0.0

     -f2    type: float
            desc: digital cutoff frequency
            default: 0.4
            bounds: value > 0.0

     -tc    type: float
            desc: gain at passband edge
            default: 0.707
            bounds: 0.000000 < [-tc] < 1.000000

     -tr    type: float
            desc: gain at stopband edge
            default: 0.316
            bounds: 0.000000 < [-tr] < 1.000000

     -c     type: integer
            desc: filter class (0 = butterworth; 1 = chebychev i;
            2 = chebychev ii)
            allowed values:
            0 (butterworth),
            1 (chebychev i),
            or 2 (chebychev ii)

EXAMPLES
SEE ALSO
     intro(1), verror(3), vgparms(3), vutils(3), ldfilthp(3)
     ldfilthp(3), dzresp(1), dfiltlp(1)

RESTRICTIONS
COPYRIGHT
     Copyright 1992, University of New Mexico.  All rights
     reserved.

Khoros                    Release: 1.0                          1

