
dfiltbs(1)                   Khoros                    dfiltbs(1)

PROGRAM
     dfiltbs - designs bandstop filters

SYNTAX
     dfiltbs

     -o             resulting output file (polynomial file)

     [-h]           sampling frequency in hertz

     [-f1]          lower rejection frequency

     [-f2]          lower cutoff frequency

     [-f3]          upper cutoff frequency

     [-f4]          upper rejection frequency

     [-tc]          gain at passband edges

     [-tr]          gain at stopband edges

     [-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 dfiltbs

     [-U]           Gives the usage for dfiltbs

     [-P]           Prompts for command line options

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

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

DESCRIPTION
     dfiltbs is a bandstop filter design program.  It is capable
     of designing Butterworth, Chebychev I, and Chebychev II
     class filters.  A filter designed by this program 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.

     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,
     whiel in the stop band it is equiripple.

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

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

     -f1    type: float
            desc: lower rejection frequency
            default: 0.1
            bounds: value > 0.0

     -f2    type: float
            desc: lower cutoff frequency
            default: 0.2
            bounds: value > 0.0

     -f3    type: float
            desc: upper cutoff frequency
            default: 0.3
            bounds: value > 0.0

     -f4    type: float
            desc: upper rejection frequency
            default: 0.4
            bounds: value > 0.0

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

     -tr    type: float
            desc: gain at stopband edges
            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), ldfiltbs(3)

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

Khoros                    Release: 1.0                          1

