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 capable 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 coefficients, 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.